Frequently Asked Questions

Can I edit my .dat data file to add some explanatory notes to the header?

Seasoft V2's Seasave (older software, replaced with Seasave V7 in 2007) created a .dat file from data acquired from the SBE 11plus V2 Deck Unit  / SBE 9plus CTD. This also applies to earlier versions of the Deck Unit and CTD.

Some text editing programs modify the file in ways that are not visible to the user (such as adding or removing carriage returns and line feeds), but that corrupt the format and prevent further processing by Seasoft. Therefore, we strongly recommend that you first convert the data to a .cnv file (using SBE Data Processing's Data Conversion module), and then use other SBE Data Processing modules to edit the .cnv file as desired.

Sea-Bird is not aware of a technique for editing a .dat file that will not corrupt it. 
Sea-Bird distributes a utility program, Fixdat, that may repair a corrupted .dat file. Fixdat.exe is installed with, and located in the same directory as, SBE Data Processing.

Note: Seasave V7 creates a .hex file instead of a .dat file from data acquired from the SBE 11plus V2 Deck Unit / SBE 9plus CTD. See the FAQ on editing a .hex file.

What do I need to send to Sea-Bird for calibration of my SBE 9plus, 25, or 25plus?

For calibration of the temperature and conductivity sensors, only the sensor modules need to be sent to Sea-Bird. It is not necessary to send the CTD main housing. See Shipping SBE 9plus, 25, and 25plus Temperature and Conductivity Sensors for details.

It is usually not necessary to recalibrate the pressure sensor as frequently as the temperature and conductivity sensors. Experience has shown that the sensor’s sensitivity function almost never changes; only the offset drifts. The offset drift can easily be measured by reading deck pressure against a barometer. This small drift is easily corrected (Seasave V7 and SBE Data Processing provide an entry for the offset drift in the instrument .con or .xmlcon file).

  • SBE 9plus and 25plus — If the pressure sensor does need to be calibrated, the entire CTD must be shipped to Sea-Bird.
  • SBE 25 — If the pressure sensor does need to be calibrated, only the modular SBE 29 pressure sensor needs to be sent to Sea-Bird. It is not necessary to send the CTD main housing.

How do instruments handle external power if internal batteries are installed?

Most Sea-Bird instruments that are designed to be powered internally or externally incorporate diode or'd circuitry, allowing only the voltage that has the greater potential to power the instrument. You can power the instrument externally without running down the internal batteries. This allows you to lab test using external power that has higher voltage than the internal batteries, and then deploy using internal power, knowing that the internal batteries are fresh.

For the SBE 25plus, if external power of 14 volts or higher is applied, the 25plus runs off of the external power, even if the main battery voltage is higher.

Can I edit my .hex data file to add some explanatory notes to the header?

Some text editing programs modify the file in ways that are not visible to the user (such as adding or removing carriage returns and line feeds), but that corrupt the format and prevent further processing by Seasoft. Therefore, we strongly recommend that you first convert the data to a .cnv file (using SBE Data Processing’s Data Conversion module), and then use other SBE Data Processing modules to edit the .cnv file as desired.

However, if you still want to edit the raw data, this procedure provides details on one way to edit a .hex data file with a text editor while retaining the required format. If the editing is not performed using this technique, Seasoft may reject the data file and give you an error message.

  1. Make a back-up copy of your .hex data file before you begin.
  2. Run WordPad.
  3. In the File menu, select Open. The Open dialog box appears. For Files of type, select All Documents (*.*). Browse to the desired .hex data file and click Open.
  4. Edit the file as desired, inserting any new header lines after the System Upload Time line. Note that all header lines must begin with an asterisk (*), and *END* indicates the end of the header. An example is shown below, with the added lines in bold:

* Sea-Bird SBE 21 Data File:
* FileName = C:\Odis\SAT2-ODIS\oct14-19\oc15_99.hex
* Software Version Seasave Win32 v1.10
* Temperature SN = 2366
* Conductivity SN = 2366
* System UpLoad Time = Oct 15 1999  10:57:19
* Testing adding header lines
* Must start with an asterisk
* Can be placed anywhere between System Upload Time and END of header

* NMEA Latitude = 30 59.70 N
* NMEA Longitude = 081 37.93 W
* NMEA UTC (Time) = Oct 15 1999  10:57:19
* Store Lat/Lon Data = Append to Every Scan and Append to .NAV File When <Ctrl F7> is Pressed
** Ship:       Sea-Bird
** Cruise:     Sea-Bird Header Test
** Station:
** Latitude:
** Longitude:
*END*

  1. In the File menu, select Save (not Save As). The following message may display:
    You are about to save the document in a Text-Only format, which will remove all formatting. Are you sure you want to do this?
    Ignore the message and click Yes.

  2. In the File menu, select Exit.

Does Sea-Bird have any calibration/service centers outside of the United States?

Sea-Bird opened a calibration/service center in Kempten, Germany in 2011, providing duty-free servicing for EU customers. The dedicated technical support staff and calibration technicians were extensively trained by Sea-Bird experts. Calibration cross-referencing between the US and Germany facilities ensures Sea-Bird factory quality and accuracy. The German facility stocks a full range of parts and supplies to support repairs. Details.

What is the maximum cable length for real-time RS-232 data?

Cable length is one of the most misunderstood items in the RS-232 world. The RS-232 standard was originally developed decades ago for a 19200 baud rate, and defines the maximum cable length as 50 feet, or the cable length equal to a capacitance of 2500 pF. The capacitance rule is often forgotten; using a cable with low capacitance allows you to span longer distances without going beyond the limitations of the standard. Also, the maximum cable length mentioned in the standard is based on 19200 baud rate; if baud is reduced by a factor of 2 or 4, the maximum length increases dramatically. Using typical underwater cables, allowable combinations of cable length and baud rate for Sea-Bird instruments communicating with RS-232 are shown below:

Maximum Cable Length (meters) Maximum Baud Rate*
1600 600
800 1200
400 2400
200 4800
100 9600
50 19,200
25 38,400
16 57,600
8 115,200

*Note: Consult instrument manual for baud rates supported for your instrument.

 

Why am I getting a class not registered error when running SBE Data Processing?

This error message typically means that some of the .dll files needed to run the software are installed incorrectly or have been corrupted. We recommend that you remove the software, and then reinstall the latest version.

Note: Use the Windows' Add or Remove Programs utility to remove the software; do not just delete the .exe file.

What are the major steps involved in taking a cast with a Profiling CTD?

Following is a brief outline of the major steps involved in taking a CTD cast, based on generally accepted practices. However, each ship, crew, and resident technicians have their own operating procedures. Each scientific group has their own goals. Therefore, observe local ship and scientific procedures, particularly in areas of safety. Before the cruise a discussion of the planned work is advisable between the ship’s crew, resident technicians, and scientific party. At this time discuss and clarify any specific ship’s procedures.

Note: The following procedure was written for an SBE 9plus CTD operating with an SBE 11plus Deck Unit. Modify the procedure as necessary for your CTD.

10 to 15 minutes before Station:

  1. Review the next cast’s plan, including proposed maximum cast depth, bottom depth, and number of bottles to close and depths. If the cast will be close to the bottom, familiarize yourself with the bottom topography.
  2. Verify that all water samples have been obtained from the bottles from the previous cast. If so, drain the bottles and cock them. Hand manipulate each Carousel latch as you cock the bottle to ensure it is free to release and is not stuck in some way.
  3. Remove the soaker tubes from the conductivity cells.
  4. Remove any other sensor covers.
  5. With permission from the deck crew, power up the CTD. Check the Deck Unit front panel display to verify communication. Perform a quick frequency check of the main sensors.
  6. Start Seasave. Set up a fixed display. Select Do not archive data for this cast. Start acquisition and view the data to verify the system is operational.
  7. Clean optical sensor windows, and perform any required air calibration.
  8. Stop acquisition. Do Not turn the CTD Deck Unit off. Select begin archiving data immediately. Set up the plot scales and status line.

5 minutes before Station:

  1. Start the ship's depth sounder and obtain a good depth reading. Be careful reading the depth sounder; if it is improperly configured the trace will wrap around the plot and be incorrect. The bottom depth should be close to the expected charted depth.
  2. Fill out any parts of the cast log that can be done at this time.

On Station, On Deck:

  1. Verify the position and the bottom depth.
  2. The computer operator should begin filling out the software header.
  3. After receiving word from the bridge that they are on station and ready to begin, untie the CTD and move it into position. If this requires hydraulics, ensure you have the appropriate people in place and permission.
  4. Position the CTD under the block. Have the winchman remove any slack from the wire.
  5. Notify the computer room that the CTD is ready for launch. The computer room should start acquiring data.
  6. Obtain a barometric pressure reading and note it on the cast sheet.
  7. When the bridge, computer room, and winchman are ready (and you have permission to proceed), put the CTD in the water.
  8. Have the winchman lower the CTD to 10 meters (his readout), hold for 1 minute, and then bring it back to the surface. One operator should remain on deck to help the winchman see when to stop the CTD. The CTD should be far enough below the surface so that the package does not break the surface in the swells.

CTD Soaking at the Surface:

  1. Finish filling out the cast log. Re-check the bottom depth.
  2. Fill out the computer software log.
  3. Hold the CTD at the surface for at least 3 minutes.
  4. Check the status line to verify that the CTD values are correct. The pressure should be the soaking depth of the CTD. Comparing the CTD temperature and salinity to the ship's thermosalinograph is helpful. Log the information (CTD and thermosalinograph) on the cast sheet.

Starting the Cast:

  1. Call the winchman and have him start the cast down. Typical lowering speed is 1 m/sec, modified for conditions as needed.
  2. Watch the computer output and verify that the system is working.

During the Cast:

  1. Closely monitor the CTD output for malfunctions. Sudden noise in a channel is often a sign of a leaking cable. A periodically flashing error light on the Deck Unit is a sign of a bad spot in the slip rings. The modulo error count (usually on the status line) provides an indication of telemetry integrity; on a properly functioning system, there will be no modulo errors.
  2. Note any odd behavior or problems on the cast sheet. Keeping good notes and records is of critical importance. While you may remember what happened an hour from now, in the months that follow, these notes will be a vital link to the cruise as you process the data.
  3. Monitor the bottom depth. This is especially critical if the cast will be close to the bottom, or you are working in an area with varying topography such as in a canyon. Running the CTD into the bottom can cause serious (and expensive) damage.

Approaching the Bottom:

  1. Take extra care if the cast will take the CTD close to the bottom. Monitor the bottom depth, pinger, and altimeter, if available. As you get within 30 meters of the bottom, slow down the cast to 0.5 m/sec. If you wish to get closer than 10 m above the bottom, slow down to 0.2 m/sec. Keep in mind that ship roll will cause the CTD depth to oscillate by several meters.
    - If the CTD does touch bottom, it will be apparent from the sudden, low salinity spike. A transmissometer, if installed, will also show a sudden low spike.
  2. Adjust these numbers and procedures as conditions dictate to avoid crashing the CTD into the bottom.
  3. When the CTD reaches the maximum cast depth, call the winchman and stop the descent.
  4. Log a position on the cast sheet. If a bottle will be closed at the bottom, allow the CTD to soak for at least 1 minute (preferably several minutes) and then close the bottle. Verify that the software records the bottle closure confirmation.
  5. Start the CTD upcast. Stop the CTD ascent at any other bottle closure depths. For each bottle, soak for at least 1 minute (preferably several minutes) and then close the bottle.

End of the Cast:

  1. As the CTD approaches the surface, have someone help spot for the winchman. Stop the CTD below the surface. Close a bottle if desired.
  2. When ready, recover the CTD. Avoid banging the system against the ship.

CTD Back on Board:

  1. Stop data acquisition and power off the CTD.
  2. Move the CTD it into its holding area and secure it.
  3. See Application Note 2D: Instructions for Care and Cleaning of Conductivity Cells for details on rinsing, cleaning, and storing the conductivity cell. Fill the conductivity cell with clean DI (or 1% Triton-X) and secure the filler device to the CTD frame. Freezing water in a conductivity cell will break the cell.
  4. See Application Note 64: SBE 43 Dissolved Oxygen Sensor - Background Information, Deployment Recommendations, and Cleaning and Storage for details on rinsing, cleaning, and storing SBE 43 (membrane-type) dissolved oxygen sensors; see the SBE 63 manual for details on rinsing, cleaning, and storing SBE 63 optical dissolved oxygen sensors.
  5. Rinse any optical sensors.
  6. Rinse the water sampler latches with clean water.
  7. Draw water samples from the bottles.

After the Cast:

  1. Re-plot the data and look at any channels that were not displayed in real time.
  2. Perform diagnostics and take a first pass through processing.
    - Verify that the data is good (at least on a first-order basis) at this point, when you can still re-do the cast. Many casts are lost because they are not analyzed until months later, when the problems are discovered.
  3. Final processing may need to wait until bottle salts and post-cruise lab calibrations are available.

Do you recommend a particular brand of alkaline D-cell batteries?

For Sea-Bird instruments that use alkaline D-cells, Sea-Bird uses Duracell MN 1300, LR20. While rare, we have seen a few problems with cheaper batteries over the years: they are more likely to leak, may vary in size (leading to loose batteries causing a bad power connection), and may not last as long.

Why and how should I align data from a 911plus CTD?

The T-C Duct on a 911plus imposes a fixed delay (lag time) between the temperature measurement and the conductivity measurement reported in a given data scan. The delay is due to the time it takes for water to transit from the thermistor to the conductivity cell, and is determined by flow rate (pump rate). The average flow rate for a 9plus is about 30 ml/sec. The Deck Unit (11plus) automatically advances conductivity (moves it forward in time relative to temperature) on the fly by a user-programmable amount (default value of 0.073 seconds), before the data is logged on your computer. This default value is about right for a typical 9plus flow rate. Any fine-tuning adjustments to this advance are determined by looking for salinity spikes corresponding to sharp temperature steps in the profile and, via the SBE Data Processing module Align CTD, trying different additions (+ or -) to the 0.073 seconds applied by the Deck Unit, until the spikes are minimized. Having found this optimum advance for your CTD (corresponding to its particular flow rate), you can use that value for all future casts (change the value in the Deck Unit) unless the CTD plumbing (hence flow rate) is changed.

Oxygen and other parameters from pumped sensors in the same flow as the CT sensors can also be re-aligned in time relative to temperature, to account for the transit time of water through the plumbing. A typical plumbing delay for the SBE 43 DO Sensor is 2 seconds. However, the DO sensor time constant varies from approximately 2 seconds at 25 °C to 5 seconds at 0 °C. So, you should add some advance time for this as well (total delay = plumbing delay + response time). As for the conductivity alignment, the Deck Unit can automatically advance oxygen on the fly by a user-programmable amount (default value of 0 seconds) before the data is logged on your computer. However, because there is more variability in the advance, most users choose to do the advance in post-processing, via the SBE Data Processing module Align CTD. For additional information and discussion, refer to Module 9 of our training class and the SBE Data Processing manual.

Note: Alignment values are actually entered in the 11plus Deck Unit and in SBE Data Processing relative to the pressure measurement. For the 9plus, it is sufficiently correct to assume that the temperature measurement is made at the same instant in time and space as the pressure measurement.

Should I collect water samples (close bottles) on the downcast or the upcast?

Most of our CTD manuals refer to using downcast CTD data to characterize the profile. For typical configurations, downcast CTD data is preferable, because the CTD is oriented so that the intake is seeing new water before the rest of the package causes any mixing or has an effect on water temperature.

However, if you take water samples on the downcast, the pressure on an already closed bottle increases as you continue through the downcast; if there is a small leak, outside water is forced into the bottle, contaminating the sample with deeper water. Conversely, if you take water samples on the upcast, the pressure decreases on an already closed bottle as you bring the package up; any leaking results in water exiting the bottle, leaving the integrity of the sample intact. Therefore, standard practice is to monitor real-time downcast data to determine where to take water samples (locations with well-mixed water and/or with peaks in the parameters of interest), and then take water samples on upcast.

When I compute sigma-density values, why are they sometimes negative?

For convenience while examining differences in density between two water parcels, Sigma-density values are typically used by oceanographers. Sigma-density values allow the oceanographer to focus on the last 6 to 7 digits in the density value (when assuming 5 decimal place resolution), as this is where most of the variation in density occurs. Sigma-density values are also a shorthand way for representing density of a water parcel with some specific modification to one of the density computational inputs, like pressure or temperature.

Examples:

  • Sigma = (rho(t,s,p) - 1000) kg/m3
  • Sigma-t = (rho(s,t,p=0) - 1000) kg/m3 (density at atmospheric pressure)
  • Sigma-theta = (rho(t=theta,s,0) - 1000 kg/m3 (density with effect of adiabatic cooling/heating effect [using potential temperature] and the pressure effect removed).


So, though the true density of water is always a value that is non-negative, when testing instruments on the bench (zero salinity) or in freshwater systems, the computed density can be < 1000 kg/m3. In this situation, when converting density to a Sigma-density value, it is possible for the Sigma-density value to be negative.

Example: S = 0, t = 5 deg C, and pressure = 0
rho(S,t,pressure) = 999.96675 kg/m3
Sigma-t (t,S,0) = - 0.03325

For more information on the Practical Salinity Scale (1978) and the Equation of State for Seawater (EOS-80), refer to UNESCO Technical Papers of Marine Science 44.

Note: Many UNESCO marine science publications are available through UNESCO's website. Go to http://unesdoc.unesco.org/ulis/ioc/.

  1. In the Series title box, select UNESCO technical papers in marine science.
  2. Select Widen the search to all UNESCO documents/publications.
  3. Click the OK button.

What are the typical data processing steps recommended for each instrument?

Section 3: Typical Data Processing Sequences in the SBE Data Processing manual provides typical data processing sequences for our profiling CTDs, moored CTDs, and thermosalinographs. Typical values for aligning, filtering, etc. are provided in the sections detailing each module of the software. This information is also documented in the software's Help file. To download the software and/or manual, go to SBE Data Processing.

Can I deploy my profiling CTD for monitoring an oil spill?

Sea-Bird CTDs can be deployed in oil; the oil will not cause long-term damage to the CTD. If the oil coats the inside of the conductivity cell and coats the dissolved oxygen sensor membrane, it can possibly affect the sensor’s calibration (and thus affect the measurement and the data). Simple measures can reduce the impact, as follows:

  1. To minimize the ingestion of oil into the conductivity cell and onto the DO sensor membrane:

SBE 19, 19plus, 19plus V2, 25, or 25plus CTD:

Set up the CTD so that the pump does not turn on until the CTD is in the water and below the layer of surface oil, minimizing ingestion of oil (however, some oil will still enter the system). Pump turn-on is controlled by two user-programmable parameters: the minimum conductivity frequency and the pump delay.

Set the minimum conductivity frequency for pump turn-on above the instrument’s zero conductivity raw frequency (shown on the conductivity sensor Calibration Sheet), to prevent the pump from turning on when the CTD is in air. Note that this is the same as our typical recommendation for setting the minimum conductivity frequency.
     For salt water and estuarine applications - typical value = zero conductivity raw frequency + 500 Hz
     For fresh/nearly fresh water - typical value = zero conductivity raw frequency + 5 Hz
If the minimum conductivity frequency is too close to the zero conductivity raw frequency, the pump may turn on when the CTD is in air as result of small drifts in the electronics. Another option is to rely only on the pump turn-on delay time to control the pump; if so, set a minimum conductivity frequency lower than the zero conductivity raw frequency.

Set the pump turn-on delay time to allow enough time for you to lower the CTD below the surface oil layer after the CTD is in the water (the CTD starts counting the pump delay time after the minimum conductivity frequency is exceeded). You may need to set the pump delay time to be longer than our typical 30-60 second recommendation.

The current minimum conductivity frequency and pump delay can be checked by sending the status command to the CTD (DS or GetCD, as applicable). Commands for modifying these parameters are:

  • SBE 19: SP (SBE 19 responds with prompts for setting up these parameters)
  • SBE 19plus and 19plus V2: MinCondFreq=x and PumpDelay=x (where x is the value you are programming).
  • SBE 25: CC (SBE 25 responds with a series of setup prompts, including setting up these parameters)
  • SBE 25plus: SetMinCondFreq=x and SetPumpDelay=x (where x is the value you are programming).

SBE 9plus CTD:

Minimum conductivity frequency and pump delay are not user-programmable for the 9plus. 

If you are using your 9plus with the 11plus Deck Unit, the Deck Unit provides power to the 9plus. Without power, the pump will not turn on. At the start of the deployment, to ensure that you have cleared the surface oil layer before the pump turns on, do not turn on the Deck Unit until the 9plus is below the surface oil layer. Similarly, on the upcast, turn off the Deck Unit before the 9plus reaches the surface oil layer.

If your 9plus is equipped with the optional manual pump control, you can enable manual pump control via the Pump Control tab in Seasave V7’s Configure Inputs dialog box. Once enabled, you can turn the pump on and off from Seasave V7’s Real-Time Control menu. Do not turn the pump on until the CTD is below the surface oil layer. On the upcast, turn the pump off before the CTD reaches the surface oil layer.

  1. To reduce the effect of the ingestion of oil into the conductivity cell and onto the DO sensor membrane or optical window:

After each recovery, rigorously follow the cleaning and storage procedures in the following application notes ‑

  • Application Note 2D: Instructions for Care and Cleaning of Conductivity Cells
  • Application Note 64: SBE 43 Dissolved Oxygen Sensor – Background Information, Deployment Recommendations, and Cleaning and Storage
  • SBE 63 Optical Dissolved Oxygen Sensor manual

Quick Reference Sheets for Oil Spill Deployment:

What is the function of the zinc anode on some instruments?

A zinc anode attracts corrosion and prevents aluminum from corroding until all the zinc is eaten up. Sea-Bird uses zinc anodes on an instrument if it has an aluminum housing and/or end cap. Instruments with titanium or plastic housings and end caps (for example, SBE 37 MicroCAT) do not require an anode.

Check the anode(s) periodically to verify that it is securely fastened and has not been eaten away.

Where can I find formulas for calculating conductivity, temperature, pressure, and derived parameters such as salinity, sound velocity, density, depth, thermosteric anomaly, specific volume, potential temperature, etc.?

For formulas for the calculation of conductivity, temperature, and pressure from the raw data, see the calibration sheets for your instrument (if you cannot find the calibration sheets, contact us with your instrument serial number at seabird@seabird.com or +1 425-643-9866).

For derived parameter formulas (salinity, sound velocity, density, etc.), see the Seasave and SBE Data Processing manuals, which document these formulas in an Appendix. Additionally, the formulas are documented in the Help files for these programs.

What are the major steps involved in deploying a moored instrument?

Application Note 83: Deployment of Moored Instruments contains a checklist, which is intended as a guideline to assist you in developing a checklist specific to your operation and instrument setup.

Why is Teflon tape used?

Adhesive Teflon tape (actually, UHMW tape — Ultra High Molecular Weight polyethylene) provides insulation to prevent damage due to contact of dissimilar metals. It is typically used by Sea-Bird on the inside of hose clamps used for mounting instruments, where U-bolts hold a Carousel Water Sampler frame to an extension stand, etc. The tape can be ordered from Sea-Bird; part number 30409 is 1 inch wide x 0.1 inch thick x 1 foot long (2.5 cm x 0.25 cm x 0.3 m). It can also be purchased from the manufacturer, Crown Plastics (see www.crownplastics.com for local distributors).

Does Sea-Bird pressure test each instrument before shipping to verify integrity of housing, o-rings, assembly, etc.?

We pressure test each Sea-Bird instrument to the smaller of:

  • The housing depth rating, or
  • (if pressure sensor installed) The maximum rating of the pressure sensor

Note: Sea-Bird does not pressure test auxiliary sensors supplied by Third Party Manufacturers that are to be integrated with Sea-Bird instruments.

What are the recommended practices for connectors - mating and unmating, cleaning corrosion, and replacing?

Mating and Unmating Connectors:

It is important to prepare and mate connectors correctly, both in terms of the costs to repair them and to preserve data quality. Leaking connectors cause noisy data and even potential system shutdowns. Application Note 57: Connector Care and Cable Installation describes the proper care and installation of connectors for Sea-Bird instruments. The Application Note covers connector cleaning and cable or dummy plug installation, locking sleeve installation, and cold weather tips.

Checking for Leakage and Cleaning Corrosion on Connectors:

If there has been leakage, it will show up as green-colored corrosion product. Performing the following steps can usually reverse the effect of the leak:

  1. Thoroughly clean the connector with water, followed by alcohol.
  2. Give the connector surfaces a light coating of silicon grease.

Re-mate the connectors properly — see Application Note 57: Connector Care and Cable Installation and 9-minute video covering O-ring, connector, and cable maintenance.

Replacing Connectors:

  • The main concern when replacing a bulkhead connector is that the o-rings on the connector and end cap must be prepared and installed correctly; if they are not, the instrument will flood. See the question below for general procedure on handling o-rings.
  • Use a thread-locking compound on the connector threads to prevent the new connector from loosening, which could also lead to flooding.
  • If the cell guard must be removed to open the instrument, take extra care not to break the glass conductivity cell.

What do you recommend for cleaning barnacles off the exterior of the instrument?

Plug the ends of the conductivity cell to prevent the cleaning solution from getting into the cell. Then soak the entire instrument in white vinegar for a few minutes. After scraping off the barnacles and marine growth, rinse the instrument well with fresh water.

We do not advise using hydrochloric acid (HCl) to clean instrument housings. Such highly corrosive acids will not hurt the anodized surfaces, but will attack any bare aluminum — including the aluminum in the cracks — and can also damage O-rings, connectors, and other sensor components.

Note: If sending the instrument to Sea-Bird for calibration, remove as much biological material as possible before shipping. Sea-Bird cannot place an instrument with a large amount of biological material on the housing in our calibration bath; if we need to clean the exterior before calibration, we will charge you for this service.

For minimizing future growth on the housing, completely wrap the instrument housing with plastic tape. The bio-organisms still grow, but after recovery it is easy to peel off the tape, shells and mussels and all!

Does Sea-Bird check and calibrate all sensors on a CTD system prior to shipping?

Your entire system is assembled and tested prior to leaving our facility, with software configured to your specific setup. All Sea-Bird manufactured instruments/sensors are calibrated in-house. Sensors from third party manufacturers are calibrated by their manufacturers prior to integration with the CTD system.

What are the recommended practices for inspecting, cleaning, and replacing o-rings?

Inspecting and Cleaning O-Rings and Mating Surfaces:

  1. Remove any water from the o-rings and mating surfaces with a lint-free cloth or tissue.
  2. Visually inspect the o-rings and mating surfaces for dirt, nicks, cuts, scratches, lint, hair, and any signs of corrosion; these could cause the seal to fail. Clean the surfaces, and clean or replace the o-rings as necessary.
  3. Apply a light, even coat of 100% silicon o-ring lubricant (Parker Super O Lube) to the o-rings and mating surfaces. For an end cap o-ring, a ball of lubricant the size of a pea is about all that is needed. Too much lubricant can cause the seal to fail as much, if not more, than no grease. Do not use petroleum-based lubricant (car grease, Vaseline, etc.), as it will cause premature failure of the rubber.
    CAUTION: Parker makes another product, Parker O Lube, that is petroleum-based. Do not use this product; verify that you are using Parker Super O Lube.
  4. After lubricating the o-ring, immediately reassemble the end cap or connector, verifying that no hairs or lint have collected on the lubricated o-ring.

Replacing O-Rings:

  • End Cap O-Rings: We recommend scheduled replacement of end cap o-rings approximately every 3 years, to prevent leaks caused by normal o-ring wear.
  • Connector O-Rings: Replacing connector o-rings requires de-soldering and re-soldering the connector wires, which makes it a more difficult task. Therefore, we recommend replacement of connector o-rings when needed, not on a routine, scheduled basis.

Additional Information:

  • 9-minute video covering O-ring, connector, and cable maintenance.
  • Short, silent video of application of lubricant to o-ring.
  • Short, silent video of application of lubricant to o-ring mating surface (note the use of a plastic dental syringe — no sharp points to scratch the housing — to apply the lubricant).

Why is the color on my instrument housing changing? Does it need to be repaired?

The housings of some of our instrument are made from anodized aluminum. In our experience it is very common to see color change when anodized housings are moored in seawater. We even see some discoloration during the brief time instruments undergo calibration and testing.

There may be several causes of discoloration:

  • Zinc from the protective anodes tends to deposit on the surface, causing the color to lighten toward gray.
  • Some seawater components, for example, carbonates, may precipitate onto the surfaces.
  • The anodized coating does not completely cover the aluminum: at microscopic scale the coating has the appearance of a dry lake bed ‑ there are patches of anodizing surrounded by cracks. These cracks allow water to reach bare aluminum and cause local oxidation that is light in color. Fortunately, once a thin oxide coating forms on aluminum, further corrosion tends to be inhibited. Unless you see severe pitting, there is usually no danger to the safety of the housing.

What language format is recommended for use with Seaterm and Seaterm V2?

For best performance and compatibility, Sea-Bird recommends that customers set their computer to English language format and the use of a period (.) for the decimal symbol. Some customers have found corrupted data when using the software's binary upload capability while set to other languages.

To update your computer's language and decimal symbol (instructions are for a Windows 7 operating system):

  1. In the computer Control Panel window, select Region and Language.
  2. In the Region and Language window, on the Formats tab, select English in the Format pull down box.
  3. In the Region and Language window, click the Additional settings . . . button. In the Customize Format window, select the period (.) in the Decimal symbol pull down box, and click OK.
  4. In the Region and Language window, click OK.

Do Sea-Bird instruments have CE certification?

There are a number of classes of products that are excluded from the EU requirement for CE certification; underwater sensors and equipment are among the types of products that do not require CE certification. However, Sea-Bird decided to obtain CE certification to ease concerns of customers in the EU.

In 2009 Sea-Bird obtained CE certification for almost all of our instruments; we have CE labels on these instruments and provide the required documentation. There is a CE label on the manual front cover for each certified instrument; see our Model List page to download the manual for a specific instrument to check for the CE label.

What is an Anti-Foulant Device? Does it affect the conductivity cell calibration? How often should I replace it? Does it require special handling?

The Anti-Foulant Device is an expendable device that is installed on each end of the conductivity cell, so that any water that enters the cell is treated. Anti-Foulant Devices are typically used with moored instruments (SBE 16, 16plus, 16plus-IM, 16plus V2, 16plus-IM V2, 37-SM, 37-SMP, 37-SMP-IDO, 37-SMP-ODO, 37-SI, 37-SIP, 37-SIP-IDO, 37-IM, 37-IMP, 37-IMP-IDO, 37-IMP-ODO), thermosalinographs (SBE 21 and 45), glider CTDs (Glider Payload CTD), moored profilers (SBE 52-MP), and drifters (SBE 41/41CP Argo float CTDs), and optionally with SBE 19plus, 19plus V2, and 49 profilers.

Anti-Foulant Devices have no effect on the calibration, because they do not affect the geometry of the conductivity cell in any way. The Anti-Foulant Devices are mounted at either end of the conductivity cell. For an in-depth explanation of how Sea-Bird makes the conductivity measurement, see Conductivity Sensors for Moored and Autonomous Operation.

Useful deployment life varies, depending on several factors. We recommend that customers consider more frequent anti-foulant replacement when high biological activity and strong current flow (greater dilution of the anti-foulant concentration) are present. Moored instruments in high growth and strong dilution environments have been known to obtain a few months of quality data, while drifters that operate in non-photic, less turbid deep ocean environments may achieve years of quality data. Experience may be the strongest determining factor in specific deployment environments. Sea-Bird recommends that you keep track of how long the devices have been deployed, to allow you to purchase and replace the devices when needed.

Note that the anti-foulant device does not actually dissolve, so there is no way to visually determine if the anti-foulant device is still effective.

The cost of the anti-foulant devices is small compared to the deployment costs, so we recommend that you replace the devices before each deployment. This will provide the maximum bio-fouling protection, resulting in long-term data quality. 

Shelf Life and Storage: The best way to store Anti-Foulant Devices is in an air-tight, opaque container. The rate of release of anti-foulant is based on saturation of the environment. The anti-foulant will release until the environment is fully saturated (100% saturated) and then it will no longer release any anti-foulant. So if you keep Anti-Foulant Devices sealed well in an air-tight container, theoretically they will stay good for extended periods of time. Exposure to direct sunlight can also affect the release of anti-foulant; we recommend storage in an opaque container.

Handling:

  • For details, refer to the Material Safety Data Sheet, enclosed with the shipment and available on our MSDS page.
  • Anti-Foulant Devices are not classified by the U.S. DOT or the IATA as hazardous material.

Why am I having trouble connecting via the SBE 39plus or SBE 56 internal USB connector?

In July 2015, Sea-Bird released updated software to address intermittent connectivity issues where the host computer or SeatermV2 cannot recognize an instrument communicating via its internal USB connector. Field Service Bulletin 28 describes the problem and the installation of updated software to solve the problem.

Do Sea-Bird instruments have ISO certification?

Sea-Bird instruments do not have ISO certification. ISO certification does not certify that a manufacturer is producing a high quality product; it merely certifies that a company has a quality control plan that complies with the quality control models adopted by the ISO organization. This does not mean that other quality control systems are inferior. Sea-Bird has intentionally not become ISO-certified, because the ISO quality control model interferes with our own and would make it much harder, slower, and more expensive to remain at the leading edge of oceanographic instrument technology and serve the best interests of ocean scientists.

What are the recommended practices for storing sensors at low temperatures, and deploying at low temperatures or in frazil or pancake ice?

General

Large numbers of Sea-Bird conductivity instruments have been used in Arctic and Antarctic programs.

Special accommodation to keep temperature, conductivity, oxygen, and optical sensors at or above 0 C is advised. Often, the CTD is brought inside protective doors between casts to achieve this.

Conductivity Cell

When freezing is possible, we recommend that the conductivity sensor be stored dry. Remove larger droplets of water by blowing through the cell. Do not use compressed air, which typically contains oil vapor. Attach a length of Tygon tubing to each end of the conductivity cell to close the cell ends. See Application Note 2D: Instructions for Care and Cleaning of Conductivity Cells for details.

There are several considerations to weigh when contemplating deployments at low temperatures in general, and in frazil or pancake ice:

  • Ensure that the instrument is at or above water temperature before it is deployed. If the cell gets colder than 0 to -2 ºC while on deck, when it enters the water a layer of ice forms inside the cell as the cell warms to ocean temperature. If ice forms inside the conductivity cell, measurements will be low of correct until the ice layer melts and disappears. Thin layers of ice will not hurt the conductivity cell, but repeated ice formation on the electrodes will degrade the conductivity calibration (at levels of 0.001 to 0.020 psu) and thicker layers of ice can lead to glass fracture and permanent damage of the cell.
  • For accurate measurements, keep ice out of the sensing region of the conductivity cell. The conductivity measurement involves determining the electrical resistance of the water inside the sensor. Ice is essentially a non-conductor. To the extent that ice displaces the water, the conductivity will register (very) misleadingly low. Some type of screening is necessary to keep ice out of the cell. This is relatively easy to arrange for the Sea-Bird conductivity cell, which is an electrode-type cell, because its sensing region is totally inside a long tube; plastic mesh could be positioned at each end and would have zero effect on accuracy and stability.

The above considerations apply to all known conductivity sensor types, whether electrode or inductive types. 

If deploying at low temperatures but no surface frazil or pancake ice is present, rinse the conductivity cell in one of the following salty solutions (salty water depresses the freezing point) to prevent freezing during deployment. But this does not mean you can store the cell in one of these solutions outside . . . it will freeze.

  • Solution of 1% Triton in sterile seawater (use 0.5-micron filtered seawater or boiled seawater),   or
  • Brine solution (distilled seawater or homemade salt solution that is higher than 35 psu in salinity).

Note that there is still a risk of forming ice inside the conductivity cell if deploying through frazil or pancake ice on the surface, if the freezing point of the salt water is the same as the water temperature. Therefore, we recommend that you deploy the conductivity cell in a dry state for these deployments.

Commercially available alcohol or glycol antifreezes contain trace amounts of oils that will coat the conductivity cell and the electrodes, causing a calibration shift, and consequently result in errors in the data. Do not use alcohol or glycol in the conductivity cell.

Temperature Sensor

In general, neither the accuracy of the temperature measurement nor the survival of the temperature sensor will be affected by ice.

Oxygen Sensor

For the SBE 43 and SBE 63 Dissolved Oxygen sensor, avoid prolonged exposure to freezing temperature, including during shipment. Do not store the with water (fresh or seawater), Triton solution, alcohol, or glycol in the plenum. The best precaution is to keep the sensor indoors or in some shelter out of the cold weather.

How accurate is salinity measured by my CTD? What factors impact accuracy?

One of the reasons that this is not a simple question is that there are several factors to take into consideration regarding the error margin for practical salinity measurements. Salinity itself is a derived measurement from temperature, conductivity, and pressure, so any errors in these sensors can propagate to salinity. For example, Oour initial accuracy specification for the SBE 3plus temperature sensor and SBE 4 conductivity sensor on an SBE 9plus CTD is approximately equivalent to an initial salinity accuracy of 0.003 PSU (note that conductivity units of mS/cm are roughly equivalent in terms of magnitude to PSU).

However, another issue to consider is that this accuracy is defined for a clean, well-mixed calibration bath. In the ocean, some of the biggest factors that impact salinity accuracy are 1) sensor drift from biofouling or surface oils for conductivity in particular and 2) dynamic errors that can occur on moving platforms, particularly when conditions are rapidly changing, which will be true for all sensors that measure salinity. Sea-Bird provides recommendations, design features such as a pumped flow path, and data processing routines to align and improve data for the salinity calculation to account for thermal transients and hysteresis, and to match sensor response times.  Depending on the environment and the steepness of the gradient, and after careful data processing, this may continue to have an impact on salinity on the order of 0.002 PSU or more, for example. For more details, see Application Note 82.

Lastly, note that salinity in PSU is calculated according to the Practical Salinity Scale (PSS-78), which is defined as valid for salinity ranges from 2 – 42 PSU.

How do I find information about the options available with each instrument?

On the product page for each instrument, there are two tabs that provide ordering information:

  • Click the Configuration tab to see all the features and options available on our price list. The Configuration tab provides explanatory information, illustrations, and photographs describing each item.
  • Click the Accessories tab to see cables, mount kits, and/or spare parts for the products.

Third Party Sensor Configuration lists instruments and integration options for sensors produced by other manufacturers (altimeters, fluorometers, transmissometers, etc.).

How many/what kind of spares should I have on ship for my SBE 9plus?

The most complete backup system would be another SBE 9plus, to allow for very rapid system swaps. This is important if your stations are close together and there is limited time between CTD casts. However, it is the most expensive option.

The next step down would be an SBE 9plus without sensors. In this case, a system failure would require swapping sensors and pumps to the new unit. This is not difficult, but it is somewhat time consuming. If you have several hours between casts it should not be a problem.

The next option would be to carry spare boards and try and troubleshoot the problem and replace boards. If you have a technician that can do this it is not a bad option. However, it requires some clean and dry lab space to open the CTD and work. You will also have to properly re-seal the CTD. Based upon experience, the SBE 9plus does not fail very often. The most common failure is the main DC-to-DC converter. Other than that, there are very few system failures. However, there are several components that can be damaged through mistakes or misuse. The most catastrophic, other that losing the whole CTD, is to plug the sea cable into the bottom contact connector on the bottom end cap; if this happens, several circuit boards will be destroyed (Note: In 2007 Sea-Bird began using a female bulkhead connector on the 9plus for the bottom contact switch, to differentiate from the sea cable connector and prevent this error. If desired, older CTDs can be retrofitted with the female connector.).

If the budget allows it, we recommend getting a complete backup SBE 9plus, including sensors. If there is any problem, return the malfunctioning instrument for repair and continue sampling with the spare instrument. A complete backup also provides you with spare sensors, so you can rotate 1 set through calibration and continue to operate.

Can I deploy a Sea-Bird CTD in freshwater, such as a river or lake?

Yes, CTDs are successfully used in many freshwater systems, such as to examine water conditions and vertical density gradients.

It is important to check that the pump on your CTD is enabled for freshwater use. For example, for the SBE 19plus V2, you should change the minimum conductivity frequency setting to enable the pump to turn on at low conductivities. The minimum conductivity frequency should be set to 1 – 5 Hz above the in-air zero raw conductivity frequency for your instrument (see the instrument calibration sheet). For extremely low conductivity systems, such as alpine lakes, you may consider setting the minimum conductivity frequency to 0. It is also important to increase the pump delay to 1 – 2 minutes, to allow enough time for the CTD to reach the water and purge all the air from the plumbing before the pump turns on. See the CTD manual for more details on configuring the pump.

In addition, for profiling CTD applications, note that the cell thermal mass corrections that Sea-Bird uses are intended for seawater. These corrections should not be applied to freshwater data; they can give bad results, due to non-linearity and the way that the derivative dC/dT is calculated in areas where conductivity changes are very small. 

Where do I find pricing information for new instruments, calibration services, and/or repair services?

Sea-Bird does not publish prices on the website. Please contact us for pricing:

Does it matter if I deploy my moored instrument, which includes a conductivity sensor, in a horizontal or vertical position?

Yes, vertical is usually preferable. In the presence of consistent currents and suspended sediment, we have seen instances where a horizontal conductivity cell is scoured by the abrasive effect of the flow. When scouring is particularly intense, the electrodes can be stripped of their electroplated platinum-black coating, driving the calibration toward fresher readings. Sedimentation (silting) in the cell also drives the readings fresh of correct.

Mounting the instrument vertically avoids abrasive flow and sediment build-up while allowing wave motions and Bernoulli pressures to flush the cell.

Note that some moored sensors (SBE 37-SIP37-SIP-IDO, 37-SMP37-SMP-IDO37-SMP-ODO37-IMP37-IMP-IDO37-IMP-ODO) have a recommended orientation because of their u-shaped plumbing configuration. Refer to the instrument manual for details.

Can I get my CTD calibrated in the low conductivity range for use in freshwater only?

No, Sea-Bird does not perform low or narrow range calibrations on our CTDs. However, CTDs are used successfully in many freshwater environments.

Conductivity calibrations performed at Sea-Bird are valid in the range of 0 – 9 S/m (or 0 – 7 S/m, as specified for some instruments), and the calibration coefficients can be applied in freshwater for accurate calculations of conductivity.

Sea-Bird recognizes that calibration using natural seawater and IAPSO standards for ocean conductivity ranges may result in a small offset and possible slope errors near zero conductivity. For example, the estimated magnitude of offset error is < 0.002 S/m, and of slope error is < 0.002 S/m per 1 S/m change. This is an example of a conservative error estimate for initial accuracy of conductivity sensors used in freshwater, which can be challenging to calculate due to lack of a freshwater standard. However, sensor precision will be near the resolution (0.00004 S/m). Sea-Bird CTDs provide high precision and sensor stability, allowing an accurate measure of conductivity gradients (dC/dz) or water sample differences, regardless of ‘true’ conductivity values.  For these reasons, Sea-Bird CTDs that have been calibrated in seawater can be used successfully in many freshwater systems.

Lastly, note that the Practical Salinity Scale (PSS-78) is defined as valid for salinity ranges from 2 – 42 PSU. For additional references on freshwater algorithms used in the limnology field, see the following literature:

  • Millero, Frank J. 2000. Equation of State for Freshwater. Aquatic Geochemistry, 6: 1 – 17.
  • Pawlowicz, R. 2008. Calculating the Conductivity of Natural Waters. L&O: Methods 6, 489 – 501.  

Which Sea-Bird profiling CTD is best for my application?

Sea-Bird makes four main profiling CTD instruments, as well as several profiling CTD instruments for specialized applications.

In order of decreasing cost, the four main profiling CTD instruments are the SBE 911plus CTD, SBE 25plus Sealogger CTD, SBE 19plus SeaCAT Profiler CTD, and SBE 49 FastCAT CTD Sensor:

  • The SBE 911plus is the world’s most accurate CTD. Used by most leading oceanographic institutions, the SBE 911plus is recognized for superior performance, reliability, and ease-of-use. Features include: modular conductivity and temperature sensors, Digiquartz pressure sensor, TC-Ducted Flow and pump-controlled time response, 24 Hz sampling, 8 A/D channels and power for auxiliary sensors, modem channel for real-time water sampler control without data interruption, and optional 9600 baud serial data uplink. The SBE 911plus system consists of: SBE 9plus Underwater Unit and SBE 11plus Deck Unit. The SBE 9plus can be used in self-contained mode when integrated with the optional SBE 17plus V2 Searam. The Searam provides battery power, internal 24 Hz data logging, and an auto-fire interface to an SBE 32 Carousel Water Sampler to trigger bottle closures at pre-programmed depths.
  • The SBE 25plus Sealogger is the choice for research work from smaller vessel not equipped for real-time operation, or use by multi-discipline scientific groups requiring configuration flexibility and good accuracy and resolution on a smaller budget. The SBE 25plus is a battery-powered, internally-recording CTD featuring the same modular C & T sensors used on the SBE 9plus CTD, an integral strain gauge pressure sensor, 16 Hz sampling, 2 GB of memory, TC-Ducted Flow and pump-controlled time response, and 8 A/D channels plus 2 RS-232 channels and power for auxiliary sensors. Real-time data can be transmitted via RS-232 simultaneous with data recording. The SBE 25plus integrates easily with an SBE 32 Carousel Water Sampler or SBE 55 ECO Water Sampler for real-time or autonomous operation.
  • The SBE 19plus V2 SeaCAT Profiler is known throughout the world for good performance, reliability, and ease-of-use. An economical, battery-powered, internally-recording mini-CTD, the SBE 19plus V2 is a good choice for basic hydrography, fisheries research, environmental monitoring, and sound velocity profiling. Features include 4 Hz sampling, 6 differential A/D channels plus 1 RS-232 channel and power for auxiliary sensors, 64 MB of memory, and pump-controlled conductivity time response. Real-time data can be transmitted via RS-232 simultaneous with data recording, The SBE 19plus V2 integrates easily with an SBE 32 Carousel Water Sampler or SBE 55 ECO Water Sampler for real-time or autonomous operation.
  • The SBE 49 FastCAT is an integrated CTD sensor intended for towed vehicle, ROV, AUV, or other autonomous profiling applications. Real-time data ‑ in raw format or in engineering units ‑ is logged or telemetered by the vehicle to which it is mounted. The SBE 49’s pump-controlled, TC-ducted flow minimizes salinity spiking, and its 16 Hz sampling provides very high spatial resolution of oceanographic structures and gradients. The SBE 49 has no memory or internal batteries. The SBE 49 integrates easily with an SBE 32 Carousel Water Sampler or SBE 55 ECO Water Sampler for real-time operation.

The specialized profiling CTD instruments are the SBE 52-MP Moored Profiler, Glider Payload CTD, and SBE 41/41CP Argo CTD module:

  • The SBE 52-MP Moored Profiler is a conductivity, temperature, pressure sensor, designed for moored profiling applications in which the instrument makes vertical profile measurements from a device that travels vertically beneath a buoy, or from a buoyant sub-surface sensor package that is winched up and down from a bottom-mounted platform. The 52-MP's pump-controlled, TC-ducted flow minimizes salinity spiking. The 52-MP can optionally be configured with an SBE 43F dissolved oxygen sensor.
  • The Glider Payload CTD measures conductivity, temperature, and pressure, and optionally, dissolved oxygen (with the modular SBE 43F DO sensor). It is a modular, low-power profiling instrument for autonomous gliders with the high accuracy necessary for research, inter-comparison with moored observatory sensors, updating circulation models, and leveraging data collection opportunities from operational vehicle missions. The pressure-proof module allows glider users to exchange CTDs (and DO sensors) in the field without opening the glider pressure hull.
  • Argo floats are neutrally buoyant at depth, where they are carried by currents until periodically increasing their displacement and slowing rising to the surface. The SBE 41/41CP CTD Module obtains the latest CTD profile each time the Argo float surfaces. At the surface, the float transmits in-situ measurements and drift track data to the ARGOS satellite system. The SBE 41/41CP can be integrated with Sea-Bird's Navis float or floats from other manufacturers. The SBE 41N CTD is integrated with Sea-Bird's Navis Float with Integrated Biogeochemical Sensors and Navis BGCi + pH Float with Integrated Biogeochemical Sensors.

See Product Selection Guide for a table summarizing the features of our profiling CTDs.

How many/what kind of spares should I have on ship for my instrument?

Very few Sea-Bird instruments completely fail due to component malfunction or manufacturing defects. However, we see a reasonably large number that require repairs of some sort. Most of these are simply due to the user breaking the equipment through rough handling, accidents, or lack of maintenance. It always best to plan for the worst case.

Parts most likely to be damaged are cables, connectors, and sensors (specifically the conductivity cell). Cables and connectors are easily replaced and spares should always be carried. After a sensor is replaced, the instrument must be re-calibrated, so it is really not practical to carry spare cells or temperature probes. If you start carrying many spare boards and sensors you are better off (both in cost and efficiency) having whole spare instruments on board.

Carrying at least 1 complete set of spares, with 3 sets of cables, connectors and dummy plugs, is recommended. How fast you can get spares from shore to the ship should dictate how many spare systems you need to have on board.

Note: See spares recommendations specific to the SBE 9plus.

I want to integrate a moored CTD with some auxiliary sensors (transmissometer, fluorometer, etc.). Which CTD should I use?

Sea-Bird currently manufactures only 1 moored CTD that can accept auxiliary sensors, the SBE 16plus V2 SeaCAT (and its inductive modem version, the 16plus-IM V2). These instruments measure conductivity and temperature; a pressure sensor is optional. They have 6 differential A/D channels and 1 RS-232 channel available for auxiliary sensors, which can be plugged into the CTD end cap.

The SBE 37 MicroCAT family includes CTDs that are integrated with a dissolved oxygen sensor at the factory.

Notes:

  • The SBE 19plus V2 SeaCAT, intended primarily for profiling applications, can also be used in moored mode. The 19plus V2 also has 6 differential A/D channels and 1 RS-232 channel available for auxiliary sensors. When in moored mode, it functions similar to a 16plus V2 with optional pressure sensor.
  • The older versions of these products, the SBE 16 / 16plus / 16plus-IM and SBE 19 / 19plus, also accept auxiliary sensors.

See Product Selection Guide for a table summarizing the features of all our moored instruments.

How will my CTD be affected by adjacent objects?

Sea-Bird’s CTDs are not directly affected by adjacent objects, unlike some CTDs that shift their calibration due to proximity effects. However, the CTD can only measure the water it sees. There are 2 concerns to keep in mind when mounting the CTD:

  • If the CTD is positioned so that the flow of water is blocked or restricted, the CTD will see water that lags behind the true environment. Also, there is a directivity affect in the conductivity measurement: The instrument measures only the conductivity of the water in its conductivity cell. This conductivity cell is oriented along the long axis of the CTD, so it will work better (i.e., get flushed with water representing the true environment) if water can flow along this axis. This is accomplished by orientation of the conductivity cell parallel to the direction of movement and with the use of a pump.
  • The thermal mass of adjacent objects can affect the temperature of the water. If the CTD is near some large object that takes a long time to equilibrate to changing temperature, the temperature of the water in the vicinity will be affected and the CTD will read this affected temperature.

How should I pick the pressure sensor range for my CTD? Would the highest range give me the most flexibility in using the CTD?

While the highest range does give you the most flexibility in using the CTD, it is at the expense of accuracy and resolution. It is advantageous to use the lowest range pressure sensor compatible with your intended maximum operating depth, because accuracy and resolution are proportional to the pressure sensor's full scale range. For example, the SBE 9plus pressure sensor has initial accuracy of 0.015% of full scale, and resolution of 0.001% of full scale. Comparing a 2000 psia (1400 meter) and 6000 psia (4200 meter) pressure sensor:

  • 1400 meter pressure sensor ‑ initial accuracy is 0.21 meters and resolution is 0.014 meters
  • 4200 meter pressure sensor ‑ initial accuracy is 0.63 meters and resolution is 0.042 meters

What are the safety concerns/procedures if the instrument floods? Can the instrument explode?

While a CTD leak can result in a dangerous situation, it is not common. Pressure housings may flood under pressure due to dirty or damaged o-rings, or other failed seals, causing highly compressed air to be trapped inside. For example, a housing that floods at 5000 meters depth holds an internal pressure of more than 7000 psia. If this happens, a potentially life-threatening situation can occur when the instrument is brought to the surface. The CTD will not explode. If it does flood and develop pressure inside, the end cap can be shot out of the housing if a technician tries to open the unit without releasing the pressure first.

Possible causes of flooding include:

  • O-rings were not properly prepared or greased after the housing was opened, or
  • Instrument was dropped or hit hard, and a bulkhead connector or the sensor was cracked or damaged.

It is important to visually inspect the instrument for damage before each survey. A cracked bulkhead connector is usually easy to spot.

If the instrument is unresponsive to commands or shows other signs of flooding or damage, see the Recovery section in your instrument manual for details specific to your instrument. For most instruments, follow these precautions:

  1. Every time you open the instrument, loosen each end cap screw a few turns. If the end cap follows the screws out, there is pressure in the housing.
  2. If pressure in the housing is indicated:
    A. Point the instrument in a safe direction away from people.
    B. Loosen 1 of the bulkhead connectors very slowly, at least 1 turn, to release the pressure safely (bulkhead connectors are the black connectors on the end cap, where the cables attach to the instrument). This opens an O-ring seal under the connector. Look for signs of internal pressure (hissing or water leak). If internal pressure is detected, let it bleed off slowly past the connector o-ring. Then, you can safely remove the end cap.

In general, instruments do not flood. However, be aware of the potential for flooding so that if a problem arises you will be able to safely deal with it.

I am ordering a CTD and want to use auxiliary sensors. Should I order them from Sea-Bird also, or deal directly with the sensors’ manufacturers?

This depends on your own expertise and resources. We have extensive experience in integrating and supporting a wide range of auxiliary sensors, but not everything under the sun. We have a large list of commonly used sensors that we routinely offer for sale (see Third Party Sensor Configuration).

When you purchase any of these auxiliary sensors from Sea-Bird, we are able to apply this experience to integrating the sensors with the CTD. The integration includes installing the sensors (with appropriate mounting kits and cables) in a manner that puts each sensor in the best possible orientation for optimum performance. It also includes configuring the CTD system and software to accept the sensors’ inputs and properly display the data, and testing the entire system, typically in a chilled saltwater bath overnight, to confirm proper operation. Having done the integration, we also support the entire system in terms of follow-on service and end-user support with operational and data analysis questions *. There is significant added value in our integration service, and there is some extra cost for this, compared to doing it yourself. However, we do not base our business on selling services, and the prices charged for Third Party sensors carry minimal mark-ups that vary depending on the pricing we are offered by the manufacturers. In some cases we can sell at the manufacturer's list price, and in others we have to add margin.

*Notes:
1. As described in our Warranty, auxiliary sensors manufactured by other companies are warranted only to the limit of the warranties provided by their original manufacturers (typically 1 year).
2. Click here for information on repairing / recalibrating auxiliary sensors manufactured by other companies.

Is it necessary to put my instrument in water to test it? Will I destroy the conductivity cell if I test it in air?

It is not necessary to put the instrument in water to test it. It will not hurt the conductivity cell to be in air.

If there is a pump on the instrument, it should not be run for extended periods in air.

  • Profiling instruments (SBE 9plus, 19, 19plus, 19plus V2, 25, 25plus, 49) and some moored instruments (all pumped MicroCATs with integral dissolved oxygen (DO), and pumped MicroCATs without DO with firmware 3.0 and later) do not turn on the pump unless the conductivity frequency is above a specified minimum value (minimum value is hard-wired in 9plus, user-programmable in other instruments). This prevents the pump from turning on in air. See the instrument manual for details.
  • If your instrument does not check for conductivity frequency before turning on the pump: 
    - For moored SeaCATs (16, 16plus, 16plus-IM, 16plus V2, 16plus-IM V2): Disconnect the pump cable for the test. 
    - For older pumped MicroCATs: orient the MicroCAT to provide an upright U-shape for the plumbing. Then fill the inside of the pump head with water via the pump exhaust tubing; this will provide enough lubrication to prevent pump damage during brief testing.

What are the pros and cons of ordering wet-pluggable connectors? Can I mate and unmate a cable with this connector underwater?

Wet-pluggable (also referred to as wet-mateable or MCBH) connectors, an option on all of our underwater instruments, may be mated in wet conditions (click here for a photo comparison). Their pins do not need to be dried before mating. By design, water on the connector pins is forced out as the connector is mated. However, they must not be mated or un-mated while submerged. Wet-pluggable connectors have a non-conducting guide pin to assist pin alignment & require less force to mate, making them easier to mate reliably under dark or cold conditions, compared to our Impulse XSG/RMG connectors (XSG/RMG connectors may not seal well in extreme cold; we recommend connecting cables in warm ship’s lab rather than on deck for these conditions). Like XSG/RMG connectors, wet-pluggables need proper lubrication & require care during use to avoid trapping water in sockets.

Wet-pluggable connectors do add additional cost to the instrument. The increase in price is dependent on the number of pins on each connector, and the number of connectors on your instrument. When should you consider configuring your instrument with wet-pluggable connectors? Consider the following guidelines:

  • Internal recording with a profiling CTD (for example, SBE 9plus with 17plus V2, SBE 19plus V2, SBE 25plus) — Connecting/disconnecting frequently to the CTD is typical for these systems, for uploading of the internally recorded data. Wet-pluggable connectors are recommended for these applications.
  • Autonomous water sampling (SBE 32 Carousel with AFM or 17plus V2, or SBE 55 ECO Water Sampler) and internal recording with a profiling CTD — Connecting/disconnecting to the underwater electronics is required after every cast, to re-arm the electronics for autonomous water sampling. Connecting/disconnecting is often done on deck, where the connectors are exposed to splashing and rain; wet-pluggable connectors are strongly recommended for these applications.
  • Real-time data acquisition with a profiling CTD (for example, SBE 9plus with 11plus Deck Unit, SBE 19plus V2 with PDIM and SBE 33 or 36 Deck Unit, SBE 25plus with PDIM and SBE 33 or 36 Deck Unit) — The underwater units in these systems are plugged into the sea cable, and typically are disconnected infrequently. Wet-pluggable connectors are not as important for this application.
  • Moored instruments
    — If data upload after recovery will occur on deck to allow for quick redeployment, wet-pluggable connectors are recommended. 
    — If data upload after recovery will occur in a lab, wet-pluggable connectors are not as important for this application.

Note: Prior to 2005, the wet-pluggable connectors available had a rubber-to-metal seal that could break down with prolonged use (3 - 5 years); seal breakdown will lead to instrument flooding. Sea-Bird recommended frequent inspection of the connectors for damage. We also discouraged the use of wet-pluggable connectors for moored deployments, because they cannot be inspected during a prolonged deployment. 
From 2005 to 2007, Sea-Bird transitioned to the WB (water block) type of wet-pluggable connectors. WB connectors have a water block that minimizes the possibility of instrument flooding; we do not discourage the use of these types of connectors for moored deployments. If you have wet-pluggable connectors on your instrument and are unsure of which type you have, contact Sea-Bird.

What are the recommended practices for cleaning and lubricating winch cables?

This topic is covered in detail on the UNOLS (University-National Oceanographic Laboratory System) website; see http://www.unols.org/publications/winch_wire_handbook__3rd_ed/06_wire_rope_em_cable_lub.PDF.

Can Sea-Bird provide some guidance for ordering cable, winch, and deck gear?

For a Sea-Bird CTD used with one of our Deck Units (SBE 11plus, SBE 33, or SBE 36), the electrical requirements of the armored cable are simple. Only one conductor is required (the armor is used as ground) and the total 2-way resistance (conductor plus armor) should be under 350 ohms. The mechanical requirements are most driven by the characteristics of the winch and weight of the payload to be lifted. The winch should have a level wind device which is either adjustable or pre-designed to lay the correct number of wraps across the drum, as determined by the cable diameter and drum width. The winch must also be equipped with a slip ring (rotating contact) assembly (at least 2 channels). A cable breaking strength of at least 5 to 7 times the maximum payload weight is recommended for safety and cable longevity. The cable must also be terminated both mechanically and electrically at the underwater (instrument) end. Cable termination (mechanical) at the winch drum is usually addressed by the winch maker. The cable is terminated electrically to the slip ring per the slip ring manufacturer's specification.

Sea-Bird is not expert in winch and deck gear and cannot recommend a block and A-frame. From past experience and with knowledge of what other customers use, we can point out sources for typical cable solutions, and cable terminations suppliers. For links to suppliers of winches, cable, and cable termination hardware, see Third Party Equipment.

What are the recommended practices for splicing cables?

Sea-Bird typically recommends using the Dam/Blok and EverGrip products from PMI Industries. DamBlok makes the electrical splice and EverGrip provides the strain relief on the cable. See an example of how these products can be used.

For a quick electrical splice in the field using commonly available materials, the UNOLS (University-National Oceanographic Laboratory System) website provides a procedure using hot glue and heat shrink: http://www.unols.org/meetings/2006/200610inm/SessionIV/SessionIV_Rowe_HOT GLUE.pdf. Numerous cycles of deployment to great depths could compromise the seal, but it may be useful for a quick fix.

How often do I need to have my instrument and/or auxiliary sensors recalibrated? Can I recalibrate them myself?

General recommendations:

  • Profiling CTD — recalibrate once/year, but possibly less often if used only occasionally. We recommend that you return the CTD to Sea-Bird for recalibration. (In principle, it is possible for calibration to be performed elsewhere, if the calibration facility has the appropriate equipment andtraining. However, the necessary equipment is quite expensive to buy and maintain.) In between laboratory calibrations, take field salinity samples to document conductivity cell drift.
  • Thermosalinograph — recalibrate at least once/year, but possibly more often depending on the degree of bio-fouling in the water.
  • DO sensor —
    — SBE 43 — recalibrate once/year, but possibly less often if used only occasionally and stored correctly (see Application Note 64), and also depending on the amount of fouling and your ability to do some simple validations (see Application Note 64-2)
    — SBE 63 — recalibrate once/year, but possibly less often if used only occasionally and stored correctly and also depending on the amount of fouling and your ability to do some simple validations (see SBE 63 manual)
  • pH sensor —
    — SBE 18 pH sensor or SBE 27 pH/ORP sensor — recalibrate at the start of every cruise, and then at least once/month, depending on use and storage
    — Satlantic SeaFET pH sensor — recalibrate at least once/year. See FAQ tab on Satlantic's SeaFET page for details (How often does the SeaFET need to be calibrated?).
  • Transmissometer — usually do not require recalibration for several years. Recalibration at the manufacturer’s factory is the most practical method.

Profiling CTDs:

We often have requests from customers to have some way to know if the CTD is out of calibration. The general character of sensor drift in Sea-Bird conductivity, temperature, and pressure measurements is well known and predictable. However, it is very difficult to know precisely how far a CTD calibration has drifted over time unless you have access to a very sophisticated calibration lab. In our experience, an annual calibration schedule will usually maintain the CTD accuracy to within 0.01 psu in Salinity.

Conductivity drifts as a change in slope as a result of accumulated fouling that coats the inside of the conductivity cell, reducing the area of the cell and causing an under-reporting of conductivity. Fouling consists of both biological growth and accumulated oils and inorganic material (sediment). Approximately 95% of fouling occurs as the cell passes through oil and other contaminants floating on the sea surface. Most conductivity fouling is episodic, as opposed to gradual and steady drift. Most fouling events are small and mostly transitory, but they have a cumulative affect over time. A severe fouling event, such as deployment through an oil spill, could have a dramatic but only partially recoverable effect, causing an immediate jump shift toward lower salinity. As fouling becomes more severe, the fit becomes increasingly non-linear and offsets and slopes no longer produce adequate correction, and return to Sea-Bird for factory calibration is required. Frequently checking conductivity drift is likely to be the most productive data assurance measure you can take. Comparing conductivity from profile to profile (as a routine check) will allow you to detect sudden changes that may indicate a fouling event and the need for cleaning and/or re-calibration.

Temperature generally drifts slowly, at a steady rate and predictably as a simple offset at the rate of about 1-2 millidegrees per year. This is approximately equal to 1-2 parts per million in Salinity error (very small).

Pressure sensor drift is also an offset, and annual comparisons to an accurate barometer to determine offset will generally keep the sensor within specification for several years, particularly as the sensors age over time.

What are the differences between salinity expressions in ppt, psu (Practical Salinity), and Absolute Salinity?

The numeric difference between psu and ppt is small; both indicate ocean salinity. Prior to 1978, oceanographers referred to the physical quantity  ppt (kg salt per kg water in parts per thousand). In 1978, the Practical Salinity Scale (PSS-78) was adopted, which yields a practical salinity from equations, smooth expansions of conductivity ratio, which were carefully fit to the real salinity of diluted North Atlantic seawater. The numeric unit from PSS-78 is psu (practical salinity unit). The primary motivation for psu was consistency; it focused on a trace to a primary conductivity standard (K15) and recognition that ocean ion ratios were not identical. Salinometer work was plagued by an inconsistent standard and the ppt equations included ion ratios from different oceans. So, the trade was a consistent standard and equation that works for a single ion mix instead of exact salinity in other ocean basins. G. Siedler and H. Peters highlighted where PSS-78 and EOS-80 formulas deviate from real salinity and density (e.g., Baltic Sea is difficult, but the deep Pacific has EOS-80 deviations of up to 0.02 kg/m3, implying salinity errors of order 0.02 psu).

In June 2009, a new Thermodynamic Equation of State of Seawater, referred to as TEOS-10, was adopted by the Scientific Committee on Oceanic Research and the International Association of Physical Sciences of the Ocean Working Group 127. The new equation incorporates a more accurate representation of salinity known as Absolute Salinity. Application Note 90 discusses this new equation, and Sea-Bird's implementation in SBE Data Processing.

How should I handle my CTD to avoid cracking the conductivity cell?

Shipping: Sea-Bird carefully packs the CTD in foam for shipping. If you are shipping the CTD or conductivity sensor, carefully pack the instrument using the original crate and packing materials, or suitable substitutes.

Use: Cracks at the C-Duct end of the conductivity cell are most often caused by:

  • Hitting the bottom, which can cause the T-C Duct to flex, resulting in cracking at the end of the cell.
  • Removing the soaker tube from the T-C duct in a rough manner, which also causes the T-C Duct to flex. Pulling the soaker tube off at an angle can be especially damaging over time to the cell. Pull the soaker tube off straight down and gently.
  • Improper disassembly of the T-C ducted temperature and conductivity sensors (SBE 25, 25plus, and 9plus) when removing them for shipment to Sea-Bird for calibration. See Shipping SBE 9plus, 25, and 25plus Temperature and Conductivity Sensors for the correct procedure.

Note: If a Tygon tube attached to the conductivity cell has dried out, yellowed, or become difficult to remove, slice (with a razor knife or blade) and peel the tube off of the conductivity cell rather than twisting or pulling the tube off.

I am planning to ship my instrument to Sea-Bird for calibration and minor repairs. What is the typical turn-around time?

Typically, Sea-Bird can calibrate the instrument and perform minor repairs within 3 - 4 weeks, plus shipping time. However, this may vary, depending on current backlog. Before shipping an instrument to us, go to our Online RMA and Service Request Form page to obtain an RMA number, so that we know your instrument is on the way and can schedule appropriately. If time is critical, contact us before shipping to verify that we can meet your schedule.

Notes:

Is the salinity calculated by Sea-Bird valid above 42 psu?

The modern oceanographic definition of salinity is the Practical Salinity Scale of 1978 (PSS-78). By definition, PSS-78 is valid only in the range of 2 to 42 psu. Sea-Bird uses the PSS-78 algorithm in our software, without regard to those limitations on the valid range.

Unesco technical papers in marine science 62 "Salinity and density of seawater: Tables for high salinities (42 to 50)" provides a method for calculating salinity in the higher range (access this paper via Unesco's website).

I am confused by all these software names. Which software does what?

Sea-Bird’s software package is called Seasoft©. Seasoft is available in both Windows and DOS versions. However, processing capability added to our software after early 2001 has been added only to the Windows versions (for example, processing data from new Sea-Bird instruments or interfacing to additional auxiliary sensors). Sea-Bird recommends that all customers use the Windows version, unless there is a compelling reason to run DOS.

Windows Software

  • Seasoft V2 — Seasoft V2 is actually a suite of stand-alone programs. You can install the entire suite or just the desired program(s).

  • Deployment Endurance Calculator — calculates deployment length for moored instruments, based on user-input deployment scheme, instrument power requirements, and battery capacity.
  • SeatermV2 — terminal program launcher that interfaces with Sea-Bird instruments developed or redesigned in 2006 and later, which can output data in XML. Can be used with SBE 16plus V2, 16plus-IM V2, 19plus V2, 25plus, 37 (SI, SIP, SM, SMP, IM, IMP, all with firmware 3.0 and later), 37 with oxygen (SIP-IDO, SIP-ODO, SMP-IDO, SMP-ODO, IMP-IDO, IMP-ODO), 39plus, 54 and PN 90588, 56, 63, and Glider Payload CTD. SeatermV2 provides setup, data retrieval, and diagnostic tests.
  • Seaterm — terminal program that interfaces with most older Sea-Bird instruments, providing setup, data retrieval, and diagnostic tests.
  • SeatermAF — terminal program that interfaces with instruments that provides auto-fire capability for autonomous operation of an SBE 32 Carousel Water Sampler (with an SBE 17plus V2 or AFM) or SBE 55 ECO Water Sampler, providing setup, data retrieval, and diagnostic tests.
  • Seasave V7 — acquires, converts, and displays real-time or archived data. Seasave V7 is an entirely new version of Seasave, officially released March 2007.
  • SBE Data Processing — converts, edits, processes, and plots data; some of SBE Data Processing’s most commonly used modules include Data Conversion, Bottle Summary, Align CTD, Bin Average, Derive, Cell Thermal Mass, Filter, and Sea Plot.
  • Plot39 — plots ASCII data that has been uploaded from SBE 39plus, 39, or 39-IM Temperature Recorder or SBE 48 Hull Temperature Sensor.
  • Seasoft for Waves-Win32
    Provides setup, data retrieval, data processing, auto-spectrum and time series analysis, statistics reporting, and plotting for the SBE 26 and SBE 26plus Seagauge Wave & Tide Recorder. Also provides setup, data retrieval, data processing, and plotting for the SBE 53 BPR Bottom Pressure Recorder.

Can I install my Sea-Bird CD-ROM on multiple computers or give it to another interested scientist?

You are free to install the software on multiple computers and to give the software to any interested potential user.

Sea-Bird's Seasoft© software is provided free of charge to Sea-Bird users and is not subject to any license. Seasoft is protected by copyright laws and international copyright treaties, as well as other intellectual property laws and treaties. All title and copyrights in and to Seasoft and the accompanying printed materials, and any copies of Seasoft, are owned by Sea-Bird Electronics. There are no restrictions on its use or distribution, provided such use does not infringe on our copyright.

The software is posted on our website, and anyone can download it.

I am planning to ship my instrument to Sea-Bird for calibration and minor repairs. Should I also send the auxiliary sensors from other manufacturers?

The answer to this question depends on your budget and your level of confidence that the entire system is functioning properly. When Sea-Bird receives CTDs that have integrated auxiliary sensors produced by other manufacturers, we test the functionality of the entire system. For a standard charge, we:

  • Visually inspect the physical condition of the auxiliary sensor, connector, and interface cable.
  • Visually inspect the mounting scheme of the auxiliary sensor on the CTD (a poor mounting scheme can result in poor data).*
  • (For voltage sensors) Measure the open voltage and block voltage to ensure that the auxiliary sensor responds through the full 0 - 5V range.
  • Check that the auxiliary sensor reads correctly when submerged in our cold salt water test baths for 30 - 60 minutes.

If the auxiliary sensor does not meet our standards*, we recommend that the sensor be sent to the other manufacturer for service. If the sensor is sent to the other manufacturer, we perform the same tests when it returns to us after servicing. Additionally, we update the configuration (.con or .xmlcon) file with any new calibration coefficients.

*Note: Sea-Bird can fix mounting scheme issues; we do not send the sensor to the other manufacturer for this.

What is the difference in temperature expressions between IPTS-68 and ITS-90?

ITS-90 was adopted in 1990 as the temperature scale; IPTS-68 was the previous standard. The differences are related to redefining certain triple points and other melt or freeze cells that are used as the fundamental standards for temperature. Over the oceanographic ranges of temperature, a linear approximation is used to convert:

IPTS-68 = 1.00024 * ITS-90

The difference is small, but at WOCE levels it is significant.

Note: Salinity, density, and sound velocity are still defined in terms of IPTS-68 temperature. Sea-Bird’s software uses IPTS-68 temperature to calculate these derived parameters, regardless of which temperature scale you select for outputting or plotting temperature.

Application Note 42: ITS-90 Temperature Scale provides a more detailed description.

How can I copy the setup of my Sea-Bird software onto another computer?

A setup file is used by Seasave V7, and by each module in SBE Data Processing, to remember the way you had the program set up. You can save the file to a desired filename and location, and then use it when you run the software the next time, to ensure that the software will be set up the same way:

  • A .psa file is created by Seasave V7 to store program settings, such as the instrument configuration (.con or .xmlcon) file name and path, serial ports, water sampler, TCP/IP ports, serial data output, etc. as well as size, placement, and setup for each display window.
  • A .psa file is created by each  module in SBE Data Processing to store program settings, such as the input filename and path, output filename, and module-specific parameters (for example, for Data Conversion: variables to convert, ascii or binary output, etc.).

If you want to set up real-time acquisition or data processing on more than one computer in the same way, simply copy the file for the desired setup, and transfer it to the other computer via your network, email, a thumb drive, or some other media. Then, after you open the software on the second computer, select the setup file you want to use.

  • Seasave V7: Select File / Open Setup File.
  • SBE Data Processing: In the module dialog box, on the File Setup tab, click the Open button under Program setup file.

My auxiliary sensor (not manufactured by Sea-Bird) needs to be repaired / recalibrated. Where should I send it for servicing?

Sea-Bird does not repair or recalibrate other manufacturers’ instruments that have been integrated with Sea-Bird equipment. If an auxiliary sensor needs to be repaired or recalibrated, we recommend that you send it directly to the manufacturer. If you send it to Sea-Bird, we will have to send it to the manufacturer, resulting in additional shipping (and possibly customs) expenses for you.

Note: Apparent malfunctioning of an auxiliary sensor can be caused by many things, including incorrect configuration (.con or .xmlcon) file, incorrect instrument setup, incorrect or leaky cables, poor mounting scheme, etc.

  • If you are not certain that the auxiliary sensor needs to be repaired, Sea-Bird can help you troubleshoot the system by phone or e-mail at no charge.
  • Alternatively, if you ship us the entire system, we can troubleshoot at the factory for our standard charges (see the FAQ above this for troubleshooting description). If we determine that the auxiliary sensor does need to be repaired, we will coordinate with you on shipment of the sensor to the manufacturer.

What is the difference between initial accuracy and resolution?

Upon receipt of an instrument, the initial accuracy is the accuracy when comparing to a known standard. Resolution is the smallest amount of change that a sensor can see.

How can I view CTD data?

You can plot the raw data from a .dat or .hex file with Seasave V7.

Once the data is converted to a .cnv file with engineering units (using SBE Data Processing’s Data Conversion), you can plot the data in SBE Data Processing’s Sea Plot.

  • Because Sea Plot only works with archived files, it is more sophisticated than Seasave. For example, Sea Plot can provide multiple file overlays, waterfall plots, and TS plots with contours.

If you wish to view the actual numbers you can open the .cnv file (if it was converted as ASCII) with any word processor or text editor.

I want to add an auxiliary sensor to my CTD (SBE 9plus, 16, 16plus, 16plus-IM, 16plus V2, 16plus-IM V2, 19, 19plus, 19plus V2, 21, 25, or 25plus). Assuming the auxiliary sensor is compatible with the instrument, what is the procedure?

Adding the sensor(s) is reasonably straightforward:

  1. Mount the sensor; a poor mounting scheme can result in poor data.
    Note: If the new sensor will be part of a pumped system, the existing plumbing must be modified; consult Sea-Bird for details.
  2. Attach the new cable.
  3. (not applicable to 9plus used with 11plus Deck Unit) Using the appropriate terminal program — Enable the channel(s) in the CTD, using the appropriate instrument command.
  4. Using Seasave V7 or SBE Data Processing — Modify the CTD configuration (.con or .xmlcon) file to reflect the new sensor, and type in the calibration coefficients.

Why is sound velocity (SV) computed from a CTD better than sound velocity from direct measuring instruments?

Direct SV probes measure the time (flight time) required for a sound pulse to travel over a fixed length, using a high-speed clock to measure time. The clock starts when the pulse is emitted, and stops when the pulse is received. Theoretically, you only need to know the path length (and frequency of the clock ‑ an easy matter) to compute SV:

SV = acoustic path length / flight time.

For a typical acoustic path of 0.1 m, a flight time of 67 microseconds is expected for SV = 1492 m/s.

Two problems associated with direct SV probes are:

  • The path length is not readily determined by a ruler measurement. The true length includes some depth into the acoustic transducer at which the pulse actually arises and again some depth where it is actually detected. Consider for example an typical instrument with specified accuracy of 0.05 m/s. For a typical water SV of 1500 m/s and a probe acoustic path of 100 mm, achieving this accuracy requires that length be determined to within (0.05/1500) x 100 mm = 0.003 mm (approximately 1/25 the thickness of a sheet of paper). The acoustic transducer would be of order 1 mm thick, so its dimension is much larger (300 times) than the length associated with the specified accuracy.
  • Determining the actual flight time is not as simple as counting clock pulses. There are other time delays in determining both the start of the acoustic pulse and the time of its reception. Recalling that the time sound requires to travel 100 mm is approximately 67 microseconds, to measure SV to within 0.05 m, the flight time must be determined to within (0.05/1492) x 67 microseconds = 2.2 nanoseconds. It is exceedingly difficult to measure time to such precision, especially as the time lag associated with the acoustic transducer is much larger than this ‑ typically of order 1 microsecond (hundreds of times larger than the permitted error).

The fact is that in designing a direct path SV probe, the determination of length by ruler is only good to 5 or 10% (approximately 100 m/s equivalent uncertainty in SV). The actual determination of SV response therefore must be made in a calibration bath (using a CTD as a reference!), which is how all SV probes are calibrated.

Direct SV probes are often marketed on the principle that the measurement is based only on fundamental physical values of length and time. That is true in theory, but the practice is a different story! Direct SV probe manufacturers do not know the length (or the time) — they just fit the probe response to CTD-computed SV. There is a place for direct SV probes. Having been calibrated in water against a CTD, they do a competent job of measuring SV in other liquids. They will go on working in oil, petrol, milk, beer, etc. — liquids in which CTD measurements have no meaning.

What is a configuration (.con or .xmlcon) file and how is it used?

The configuration file defines the instrument — auxiliary sensors integrated with the instrument, and channels, serial numbers, and calibration dates and coefficients for all the integrated sensors (conductivity, temperature, and pressure as well as auxiliary sensors). Sea-Bird’s real-time acquisition and data processing software uses the information in the configuration file to interpret and process the raw data (sensor frequencies and voltages). If the configuration file does not match the actual instrument configuration, the software will not be able to interpret and process the data correctly.

When Sea-Bird ships a new instrument, we include a .con or .xmlcon file that reflects the current instrument configuration. The file is named with the instrument serial number, followed with the .con or .xmlcon extension. For example, for an instrument with serial number 2375, Sea-Bird names the .xmlcon file 2375.xmlcon. You may rename the configuration file if desired; this will not affect the results.
(Click here to see an example of where to find the serial number on your instrument)

Seasave V7 and SBE Data Processing version 7.20 (2009) introduced .xmlcon files (in XML format). Versions 7.20 and later allow you to open a .con or .xmlcon file, and to save it to a .con or .xmlcon file.

To view or modify the configuration file, use the Configure Inputs menu in Seasave V7, or the Configure menu in SBE Data Processing.

Notes:

  • Seasave V7 and SBE Data Processing check that the serial number in the configuration file matches the instrument serial number in the .dat or .hex data file. If they are not the same, you will get an error message. The instrument serial number can be verified by sending the Status command (DS or #iiDS, as applicable) in the appropriate terminal program.
  • SBE 16, 16plus, 16plus-IM, 16plus V2, 16plus-IM V2, 19, 19plus, 19plus V2, 21, and 49 — The instrument serial number is the same as the serial number of both the conductivity and temperature sensors.
  • SBE 37 (older), 39, 39plus, and 48 — These instruments store calibration coefficients internally and do not accept auxiliary sensors, so they do not have configuration files.
  • SBE 37 (newer) that is compatible with SeatermV2 terminal program — SeatermV2 creates a configuration file for these instruments when it uploads data. The configuration file can then be used for processing the data in SBE Data Processing.
  • The calibration date in the configuration file is for information only. It does not affect the data processing.
  • When Sea-Bird recalibrates an instrument, we ship the instrument with a Calibration Sheet showing the new calibration coefficients (1 calibration sheet per sensor on the instrument that was calibrated). Sea-Bird also supplies a .xml file with the calibration coefficients for each calibrated sensor. The .xml files can be imported into Seasave or SBE Data Processing, to update the calibration coefficients in the configuration file.
    — For CTDs: Sea-Bird also creates a new configuration file, which includes calibration coefficients for the CTD as well as any auxiliary sensors that were returned to Sea-Bird with the CTD. If you did not return the auxiliary sensors with the CTD, you need to update the configuration file to include information on the auxiliary sensors that you plan to deploy with your CTD.

Do I need to remove batteries before shipping my instrument for a deployment or to Sea-Bird?

Alkaline batteries can be shipped installed in the instrument. See Shipping Batteries for information on shipping instruments with Lithium or Nickel-Metal Hydride (NiMH) batteries.

Which algorithm for calculating sound velocity (SV) from CTD data should I use?

Sea-Bird real-time data acquisition (Seasave V7) and data processing (SBE Data Processing) software supports calculation of Chen-Millero, Del Grosso, and Wilson sound velocities. The algorithms, as implemented in our software, are provided in the software documentation, which is available via the software Help files or in an Appendix in the software manuals.

The Hydrographic Society published Special Publication No. 34 in 1993, "A Comparison Between Algorithms for the Speed of Sound in Seawater", comparing a number of sound velocity algorithms. The report recommends using the Chen-Millero algorithm for water depths less than 1000 meters and the Del Grosso algorithm for water depths greater than 1000 meters, and recommends that the Wilson algorithm should not be used. Access the report via the Hydrographic Society's website.

What is a .psa file and how is it used?

A .psa (program setup) file is used by Seasave V7 and by each module in SBE Data Processing to remember the way you had the program set up. You can save the .psa file to a desired filename and location, and then use it when you run the software the next time, to ensure that the software will be set up the same way:

  • A .psa file is created by Seasave V7 to store program settings, such as the instrument configuration (.con or .xmlcon) file name and path, serial ports, water sampler, TCP/IP ports, serial data output, etc. as well as size, placement, and setup for each display window.
  • A .psa file is created by each  module in SBE Data Processing to store program settings, such as the input filename and path, output filename, and module-specific parameters (for example, for Data Conversion: variables to convert, ascii or binary output, etc.).

If you want to set up real-time acquisition or data processing on more than one computer in the same way, simply copy the .psa file for the desired setup, and transfer it to the other computer via your network, email, a CD-ROM, or some other media. Then, after you open the software on the second computer, select the .psa file you want to use.

  • Seasave V7: Select File / Open Setup File.
  • SBE Data Processing: In the module dialog box, on the File Setup tab, click the Open button under Program setup file.

Do I need to clean the exterior of my instrument before shipping it to Sea-Bird for calibration?

Remove as much biological material and/or anti-foul coatings as possible before shipping. Sea-Bird cannot place an instrument with a large amount of biological material or anti-foul coating on the housing in our calibration bath; if we need to clean the exterior before calibration, we will charge you for this service.

  • To remove barnacles, plug the ends of the conductivity cell to prevent the cleaning solution from getting into the cell. Then soak the entire instrument in white vinegar for a few minutes. After scraping off the barnacles and marine growth, rinse the instrument well with fresh water.
  • To remove anti-foul paint, use a Heavy Duty Scotch-Brite pad (http://www.3m.com/us/home_leisure/scotchbrite/products/scrubbing_scouring.html) or similar scrubbing device.

How can I find the density of seawater at different temperatures and/or salinities?

SBE Data Processing includes a module called Seacalc III. Seacalc III can calculate density, sound velocity, and a number of other parameters for a given user input of pressure, temperature, and conductivity (or salinity).

Does Seasoft have a provision for converting to MatLab data files?

MatLab can import flat ASCII files. To produce those files:

  1. Run SBE Data Processing’s Data Conversion module to produce a .cnv file with data in ASCII engineering units from the raw data file. This file also contains header information.
  2. Run SBE Data Processing’s ASCII Out module to remove the header information, outputting just the data portion of the converted data file to a .asc file. Optionally, you can also output the header information to a .hdr file.

I want to change the pressure sensor on my CTD, swapping it as needed to get the best data for a given deployment depth. Can I do this myself, or do I need to send the instrument to Sea-Bird?

On most of our instruments, replacement of the pressure sensor should be performed at Sea-Bird. We cannot extend warranty coverage if you replace the pressure sensor yourself.

However, we recognize that you might decide to go ahead and do it yourself because of scheduling/cost issues. Some guidelines follow:

  1. Perform the swap and carefully store the loose sensor on shore in a laboratory or electronics shop environment, not on a ship. The pressure sensor is fairly sensitive to shock, and a loose sensor needs to be stored carefully. Dropping the sensor will break it.
  2. Some soldering and unsoldering is required. Verify that the pressure sensor is mounted properly in your instrument. Properly re-grease and install the o-rings, or the instrument will flood.
  3. Once the sensor is installed, back-fill it with oil. Sea-Bird uses a vacuum-back filling apparatus that makes this job fairly easy. We can provide a drawing showing the general design of the apparatus, which can be modified and constructed by your engineers.
  4. For the most demanding work, calibrate the sensor on a deadweight tester to ensure proper operation and calibration.
  5. Enter the calibration coefficients for the new sensor in:
  • the CTD configuration (.con or .xmlcon) file, using Seasave V7 or SBE Data Processing, and
  • (for an instrument with internally stored calibration coefficients) the CTD EEPROM, using the appropriate terminal program and the appropriate calibration coefficient commands

Note: This discussion does not apply to the SBE 25 (not 25plus), which uses a modular pressure sensor (SBE 29) mounted externally on the CTD. Swap the SBE 29 as desired, use the CC command in Seaterm or SeatermAF to enter the new pressure range and pressure temperature compensation value, and type the calibration coefficients for the new sensor into the CTD configuration (.con or .xmlcon) file in Seasave V7 or SBE Data Processing.

What is the cause of conductivity drift?

Conductivity cells drift primarily as a function of cell fouling. There are several sources of the fouling:

  • Biological growth is the primary source of cell fouling. Rinsing the conductivity cell with clean de-ionized water after each cast helps prevent most growth in the cell. If the cell is not rinsed, or standard tap water is used, growth rates can be severe. As the cell fouls, it will drift towards lower salinity values.
  • Surface oil slicks also cause cell fouling. Avoid deploying the CTD through obvious slicks. When working in coastal areas, with higher chances of oil fouling, rinse and soak the cell with a 1% Triton X-100 solution (diluted in clean DI water) to help prevent oil fouling.

See Application Note 2D: Instructions for Care and Cleaning of Conductivity Cells for rinsing, cleaning, and storage procedures.

Because of the nature of fouling, the total cell drift may not be linear. It exhibits rapid small shifts (especially if related to oil fouling) on top of a base line drift. It is important to take water samples to document the behavior. Application Note 31: Computing Temperature and Conductivity Slope and Offset Correction Coefficients from Laboratory Calibrations and Salinity Bottle Samples discusses how to correct the data.

What operating systems are compatible with Seasoft?

Current Sea-Bird software was designed to work on a PC running Windows XP service pack 2 or later, Windows Vista, or Windows 7 (both 32-bit and 64-bit). We chose Windows because of its widespread availability, and suitability as an acquisition platform. Sea-Bird provides the software free of charge as part of our instrument support. Because of this, we do not have the resources to write and provide support software for other operating systems, such as Apple, Unix, or Linux.

  • If you have a valid PC emulator on your system, the Sea-Bird software may run, but we have no way to confirm this, or that the I/O connections to the instrument will properly function.
  • If you have access to a PC running Windows, you can use Sea-Bird’s software to convert the data from our proprietary format to ASCII (in engineering units of C, T, P, etc. with calibration coefficients applied); then you could use your own software on a different computer to perform additional processing.

Can I brush-clean and replatinize the conductivity cell myself? How often should this be done?

Brush-cleaning and replatinizing should be performed at Sea-Bird. We cannot extend warranty coverage if you perform this work yourself.

The brush-cleaning and replatinizing process requires specialized equipment and chemicals, and the disassembly of the sensor. If performed incorrectly, you can damage the cell. Additionally, the sensor must be re-calibrated when the work is complete.

Sea-Bird determines whether brush-cleaning and replatinizing is required based upon how far the calibration has drifted from the original calibration. Typically, a conductivity sensor on a profiling CTD requires brush-cleaning and replatinizing every 5 years.

Does it matter whether you use natural or artificial seawater for calibrations? Which does Sea-Bird use?

For SBE 4 conductivity calibrations, Sea-Bird uses natural seawater that has been carefully collected, stored, UV irradiated, and filtered. Artificial seawater is not adequate if calibration errors are to be kept below 0.010 psu.
Note: SBE 4 is the conductivity sensor in the SBE 9plus, 25, and 25plus profiling CTDs.

The primary difference between natural and artificial seawater is the behavior of conductivity versus temperature. The practical salinity scale 1978 equations include a term rt. This term is expanded into a fourth order equation that describes the variation of conductivity versus temperature for a sample of constant salinity. The equation’s coefficients are derived by fitting to natural seawater samples. Artificial seawater does not have the same conductivity versus temperature characteristic, providing incorrect coefficients and causing a slope error in the calibration.

For calibrations of conductivity sensors other than the SBE 4, Sea-Bird uses artificial seawater (NaCl solution). However, we place an SBE 4 conductivity sensor in each bath, providing a standard for reference to the natural seawater calibration. This allows us to correct errors in the coefficients and slope introduced with the artificial seawater calibration.

For calibration of temperature sensors, Sea-Bird uses artificial seawater (NaCl solution).

What is the flag variable column that is added to the data file by SBE Data Processing's Data Conversion or ASCII In module?

The flag variable column is added by Data Conversion (if you process data using Sea-Bird software) or ASCII In (if you are importing data that was generated using other software). The Loop Edit module sets the flag variable to bad for scans that show a pressure slowdown or reversal. The flag variable is then used by the rest of the SBE Data Processing modules as an indication of a bad scan, allowing you to exclude scans that are marked bad from processing performed in a module, if desired.

Initially all scans are marked good (flag value of 0) in Data Conversion or ASCII In. A flag of -9.99e-29 indicates the scan has been marked bad by Loop Edit.

Note: All occurrences of the bad value (-9.99e-29) can be replaced with a different value in ASCII Out. This may be useful for plotting purposes, as -9.99e-29 looks like 0 in a data plot.

I sent my conductivity sensor to Sea-Bird for calibration, and you also performed a Cleaning and Replatinizing (C &P). You sent the instrument back with 2 sets of calibration data. What does this mean?

The post-cruise calibration contains important information for drift calculations. The post-cruise calibration is performed on the cell as we received it from you, and is an indicator of how much the sensor has drifted in the field. Information from the post-cruise calibration can be used to adjust your data, based on the sensor’s drift over time. See Application Note 31: Computing Temperature and Conductivity Slope and Offset Correction Coefficients from Laboratory Calibrations and Salinity Bottle Samples.

If the sensor has drifted significantly (based on the data from the post-cruise calibration), Sea-Bird performs a C & P to restore the cell to a state similar to the original calibration. After the C & P, the sensor is calibrated again. This calibration serves as the starting point for future data, and for the sensor’s next drift calculation.

The C & P tends to return the cell to its original state. However, there are many subtle factors that may result in the post-C & P calibration not exactly matching the original calibration. Basically, the old platinizing is stripped off and new platinizing is plated on. Anything in this process that alters the cell slightly will result in a difference from the original calibration. We compare the calibration after C & P with the original calibration, not to make any drift analysis, but to make sure we did not drastically alter the cell, or that the cell was not damaged during the C & P process.

Where can I purchase standard seawater?

IAPSO standard seawater is available in 250 ml vials. For more information and purchase inquiry, e-mail osil@oceanscientific.co.uk.

How does Sea-Bird software calculate conductivity, temperature, and pressure in engineering units?

For formulas for the calculation of conductivity, temperature, and pressure from the raw data, see the calibration sheets for your instrument. If you cannot find the calibration sheets, contact us with your instrument serial number (Click here to see an example of where to find the serial number on your instrument).

How can I tell if the conductivity cell on my CTD is broken?

Conductivity cells are made of glass, which is breakable.

  • If a cell is cracked, it typically causes a salinity shift or erratic data.
  • However, if the crack occurs at the end of the cell, the sensor will continue to function normally until water penetrates the epoxy jacket. Post-cruise calibration results will reveal whether or not water has penetrated the epoxy jacket.

Inspect the cell thoroughly and make sure that it isn’t cracked or abused in any way.

  • (SBE 9plus, 25, or 25plus) If the readings are good at the surface but erratic at depth, it is likely that the problem is in the cable or the connector, not the conductivity cell. Check the connections, making sure that you burp the connectors when you plug them in (see Application Note 57: Connector Care and Cable Installation). Check the cable itself (swap with a spare cable, if available).
  • If the readings are incorrect at the surface but good after a few meters, it is likely that the problem is flow-related. Verify that the pump is working properly. Check the air bleed valve (the white plastic piece in the Y-fitting, which is installed on vertically deployed CTDs) to see if it is clogged; clean out the small hole with a piece of fine wire supplied with your CTD.
  • If the readings are incorrect for the entire cast, there may be an incorrect calibration coefficient or the cell may be cracked.
  • Check the conductivity calibration coefficients in the configuration (.con or .xmlcon) file.
  • Do a frequency check on the conductivity cell. Disconnect the plumbing on the cell. Rinse the cell with distilled or de-ionized water and blow it dry (use your mouth and not compressed air, as there tends to be oil in the air lines on ships). With the cell completely dry, check the frequency reading. It should read within a few tenths of a Hz of the 0 reading on your Calibration Sheet. If it does not, something is wrong with the cell and it needs to be repaired.

Why is my CTD data showing hysteresis?

The difference between downcast and upcast is most likely related to package wake. When the CTD is mounted under a large water sampler, the variation can be on the order of 5 to 8 meters. This is due to the shadowing of the CTD sensors by the water sampler.

How does Sea-Bird software calculate derived variables such as salinity, sound velocity, density, depth, thermosteric anomaly, specific volume, potential temperature, etc.?

The Seasave and SBE Data Processing manuals document the derived variable formulas in an Appendix (Derived Parameter Formulas). The Help files for these programs also document the formulas. To download the software and/or manuals, go to Software.

What are Configuration Sheets, and where can I find them for my instrument?

Configuration Sheets detail instrument communication settings, system configuration (auxiliary sensors, which channels are set up for which sensors), and sensor calibration coefficients. Configuration sheets are provided with the instrument, in both paper form (may be part of the manual) and on the CD-ROM.

Configuration Sheet locations vary, depending on the type of instrument and when it was shipped. If you cannot locate them, contact Sea-Bird and we will email copies.

Can I use a pressure sensor above its rated pressure?

Digiquartz pressure sensors are used in the SBE 9plus, 53, and 54. The SBE 16plus V2, 16plus-IM V2, 19plus V2, and 26plus can be equipped with either a Druck pressure sensor or a Digiquartz pressure sensor. All other instruments that include pressure use a Druck pressure sensor.

  • The overpressure rating for a Digiquartz (as stated by Paroscientific) is 1.2 * full scale. The sensor will provide data values above 100% of rated full scale; however, Sea-Bird does not calibrate beyond the rated full scale.
  • The overpressure rating for a Druck (as stated by Druck) is 1.5 * full scale. The sensor will provide data values above 100% of rated full scale; however, Sea-Bird does not calibrate beyond the rated full scale.

Note: If you use the instrument above the rated range, you do so at your own risk; the product will not be covered under warranty.

What formula does Sea-Bird software use to convert pressure data to depth?

What is Sea-Bird’s policy on upgrading instruments?

It is our policy to update firmware in instruments while they are here for calibration at no cost to the customer, but it is not our policy to routinely upgrade circuit cards. On some very old units that are being upgraded to support more external sensors, new pressure sensors, or other repairs, we sometimes discount the new circuit cards as part of the larger upgrade, as that makes the work easier for us to complete.

Where can I get information about safe handling/hazards associated with chemicals used with Sea-Bird equipment, such as Anti-Foulant Devices and Triton X-100 detergent?

See Material Safety Data Sheets (MSDS) for chemicals commonly used with Sea-Bird instruments.

In Sea-Bird software, is noon on January 1 Julian Day 0.5 or Julian Day 1.5?

In Seasoft-DOS version 4.249 and higher (March 2001 and later), January 1 is Julian Day 1. Therefore, noon on January 1 is Julian Day 1.5. Earlier versions of the software incorrectly defined January 1 as Julian Day 0, so noon on January 1 would appear as Julian Day 0.5.

All release versions of SBE Data Processing correctly identify January 1 as Julian Day 1.

Should I purchase spare sensors for my SBE 9plus or 25plus?

Most customers purchase spare conductivity and temperature sensors. These sensors are exposed to ocean conditions and therefore more likely to be broken than an internal sensor. It is also very easy to change them because they are independent sensors that plug into the CTD main housing.

Most customers do not purchase spare pressure sensors for the following reasons:

  • The pressure sensor is inside the CTD main housing. It is very well protected against damage of any kind, and reliability of this sensor is extremely good.
  • The sensor is expensive.
  • It is difficult to change the sensor in the field.

What is Triton? Do I need to purchase it from Sea-Bird?

Triton X-100 is Octyl Phenol Ethoxylate, a reagent grade non-ionic surfactant (detergent). Sea-Bird uses it to help keep our conductivity cells clean and the electrodes wetted and ready for immediate use in water (a dry cell requires a few minutes to become completely wetted after immersion). Triton X-100 will not harm conductivity cells, temperature sensors, or pumped fluorometers. Do not place concentrated Triton X-100 directly on the membrane or optical window of a dissolved oxygen sensor.

Triton X-100 is supplied in 100% strength.

Triton X-100 can be ordered from Sea-Bird, but should also be available locally from a chemical supply or laboratory products companies. It is manufactured by Avantor Performance Materials (see http://www.avantormaterials.com/commerce/product.aspx?id=2147509608). See our MSDS page to view the Material Safety Data Sheet.

Can I edit my .hex data file to add some explanatory notes to the header?

Some text editing programs modify the file in ways that are not visible to the user (such as adding or removing carriage returns and line feeds), but that corrupt the format and prevent further processing by Seasoft. Therefore, we strongly recommend that you first convert the data to a .cnv file (using SBE Data Processing’s Data Conversion module), and then use other SBE Data Processing modules to edit the .cnv file as desired.

However, if you still want to edit the raw data, this procedure provides details on one way to edit a .hex data file with a text editor while retaining the required format. If the editing is not performed using this technique, Seasoft may reject the data file and give you an error message.

  1. Make a back-up copy of your .hex data file before you begin.
  2. Run WordPad.
  3. In the File menu, select Open. The Open dialog box appears. For Files of type, select All Documents (*.*). Browse to the desired .hex data file and click Open.
  4. Edit the file as desired, inserting any new header lines after the System Upload Time line. Note that all header lines must begin with an asterisk (*), and *END* indicates the end of the header. An example is shown below, with the added lines in bold:

* Sea-Bird SBE 21 Data File:
* FileName = C:\Odis\SAT2-ODIS\oct14-19\oc15_99.hex
* Software Version Seasave Win32 v1.10
* Temperature SN = 2366
* Conductivity SN = 2366
* System UpLoad Time = Oct 15 1999  10:57:19
* Testing adding header lines
* Must start with an asterisk
* Can be placed anywhere between System Upload Time and END of header

* NMEA Latitude = 30 59.70 N
* NMEA Longitude = 081 37.93 W
* NMEA UTC (Time) = Oct 15 1999  10:57:19
* Store Lat/Lon Data = Append to Every Scan and Append to .NAV File When <Ctrl F7> is Pressed
** Ship:       Sea-Bird
** Cruise:     Sea-Bird Header Test
** Station:
** Latitude:
** Longitude:
*END*

  1. In the File menu, select Save (not Save As). The following message may display:
    You are about to save the document in a Text-Only format, which will remove all formatting. Are you sure you want to do this?
    Ignore the message and click Yes.

  2. In the File menu, select Exit.

Why am I getting a class not registered error when running SBE Data Processing?

This error message typically means that some of the .dll files needed to run the software are installed incorrectly or have been corrupted. We recommend that you remove the software, and then reinstall the latest version.

Note: Use the Windows' Add or Remove Programs utility to remove the software; do not just delete the .exe file.

Why and how should I align data from a 911plus CTD?

The T-C Duct on a 911plus imposes a fixed delay (lag time) between the temperature measurement and the conductivity measurement reported in a given data scan. The delay is due to the time it takes for water to transit from the thermistor to the conductivity cell, and is determined by flow rate (pump rate). The average flow rate for a 9plus is about 30 ml/sec. The Deck Unit (11plus) automatically advances conductivity (moves it forward in time relative to temperature) on the fly by a user-programmable amount (default value of 0.073 seconds), before the data is logged on your computer. This default value is about right for a typical 9plus flow rate. Any fine-tuning adjustments to this advance are determined by looking for salinity spikes corresponding to sharp temperature steps in the profile and, via the SBE Data Processing module Align CTD, trying different additions (+ or -) to the 0.073 seconds applied by the Deck Unit, until the spikes are minimized. Having found this optimum advance for your CTD (corresponding to its particular flow rate), you can use that value for all future casts (change the value in the Deck Unit) unless the CTD plumbing (hence flow rate) is changed.

Oxygen and other parameters from pumped sensors in the same flow as the CT sensors can also be re-aligned in time relative to temperature, to account for the transit time of water through the plumbing. A typical plumbing delay for the SBE 43 DO Sensor is 2 seconds. However, the DO sensor time constant varies from approximately 2 seconds at 25 °C to 5 seconds at 0 °C. So, you should add some advance time for this as well (total delay = plumbing delay + response time). As for the conductivity alignment, the Deck Unit can automatically advance oxygen on the fly by a user-programmable amount (default value of 0 seconds) before the data is logged on your computer. However, because there is more variability in the advance, most users choose to do the advance in post-processing, via the SBE Data Processing module Align CTD. For additional information and discussion, refer to Module 9 of our training class and the SBE Data Processing manual.

Note: Alignment values are actually entered in the 11plus Deck Unit and in SBE Data Processing relative to the pressure measurement. For the 9plus, it is sufficiently correct to assume that the temperature measurement is made at the same instant in time and space as the pressure measurement.

What are the typical data processing steps recommended for each instrument?

Section 3: Typical Data Processing Sequences in the SBE Data Processing manual provides typical data processing sequences for our profiling CTDs, moored CTDs, and thermosalinographs. Typical values for aligning, filtering, etc. are provided in the sections detailing each module of the software. This information is also documented in the software's Help file. To download the software and/or manual, go to SBE Data Processing.

Where can I find formulas for calculating conductivity, temperature, pressure, and derived parameters such as salinity, sound velocity, density, depth, thermosteric anomaly, specific volume, potential temperature, etc.?

For formulas for the calculation of conductivity, temperature, and pressure from the raw data, see the calibration sheets for your instrument (if you cannot find the calibration sheets, contact us with your instrument serial number at seabird@seabird.com or +1 425-643-9866).

For derived parameter formulas (salinity, sound velocity, density, etc.), see the Seasave and SBE Data Processing manuals, which document these formulas in an Appendix. Additionally, the formulas are documented in the Help files for these programs.

Which algorithm for calculating sound velocity (SV) from CTD data should I use?

Sea-Bird real-time data acquisition (Seasave V7) and data processing (SBE Data Processing) software supports calculation of Chen-Millero, Del Grosso, and Wilson sound velocities. The algorithms, as implemented in our software, are provided in the software documentation, which is available via the software Help files or in an Appendix in the software manuals.

The Hydrographic Society published Special Publication No. 34 in 1993, "A Comparison Between Algorithms for the Speed of Sound in Seawater", comparing a number of sound velocity algorithms. The report recommends using the Chen-Millero algorithm for water depths less than 1000 meters and the Del Grosso algorithm for water depths greater than 1000 meters, and recommends that the Wilson algorithm should not be used. Access the report via the Hydrographic Society's website.

How can I find the density of seawater at different temperatures and/or salinities?

SBE Data Processing includes a module called Seacalc III. Seacalc III can calculate density, sound velocity, and a number of other parameters for a given user input of pressure, temperature, and conductivity (or salinity).

What language format is recommended for use with Seaterm and Seaterm V2?

For best performance and compatibility, Sea-Bird recommends that customers set their computer to English language format and the use of a period (.) for the decimal symbol. Some customers have found corrupted data when using the software's binary upload capability while set to other languages.

To update your computer's language and decimal symbol (instructions are for a Windows 7 operating system):

  1. In the computer Control Panel window, select Region and Language.
  2. In the Region and Language window, on the Formats tab, select English in the Format pull down box.
  3. In the Region and Language window, click the Additional settings . . . button. In the Customize Format window, select the period (.) in the Decimal symbol pull down box, and click OK.
  4. In the Region and Language window, click OK.

Why am I having trouble connecting via the SBE 39plus or SBE 56 internal USB connector?

In July 2015, Sea-Bird released updated software to address intermittent connectivity issues where the host computer or SeatermV2 cannot recognize an instrument communicating via its internal USB connector. Field Service Bulletin 28 describes the problem and the installation of updated software to solve the problem.

I am confused by all these software names. Which software does what?

Sea-Bird’s software package is called Seasoft©. Seasoft is available in both Windows and DOS versions. However, processing capability added to our software after early 2001 has been added only to the Windows versions (for example, processing data from new Sea-Bird instruments or interfacing to additional auxiliary sensors). Sea-Bird recommends that all customers use the Windows version, unless there is a compelling reason to run DOS.

Windows Software

  • Seasoft V2 — Seasoft V2 is actually a suite of stand-alone programs. You can install the entire suite or just the desired program(s).

  • Deployment Endurance Calculator — calculates deployment length for moored instruments, based on user-input deployment scheme, instrument power requirements, and battery capacity.
  • SeatermV2 — terminal program launcher that interfaces with Sea-Bird instruments developed or redesigned in 2006 and later, which can output data in XML. Can be used with SBE 16plus V2, 16plus-IM V2, 19plus V2, 25plus, 37 (SI, SIP, SM, SMP, IM, IMP, all with firmware 3.0 and later), 37 with oxygen (SIP-IDO, SIP-ODO, SMP-IDO, SMP-ODO, IMP-IDO, IMP-ODO), 39plus, 54 and PN 90588, 56, 63, and Glider Payload CTD. SeatermV2 provides setup, data retrieval, and diagnostic tests.
  • Seaterm — terminal program that interfaces with most older Sea-Bird instruments, providing setup, data retrieval, and diagnostic tests.
  • SeatermAF — terminal program that interfaces with instruments that provides auto-fire capability for autonomous operation of an SBE 32 Carousel Water Sampler (with an SBE 17plus V2 or AFM) or SBE 55 ECO Water Sampler, providing setup, data retrieval, and diagnostic tests.
  • Seasave V7 — acquires, converts, and displays real-time or archived data. Seasave V7 is an entirely new version of Seasave, officially released March 2007.
  • SBE Data Processing — converts, edits, processes, and plots data; some of SBE Data Processing’s most commonly used modules include Data Conversion, Bottle Summary, Align CTD, Bin Average, Derive, Cell Thermal Mass, Filter, and Sea Plot.
  • Plot39 — plots ASCII data that has been uploaded from SBE 39plus, 39, or 39-IM Temperature Recorder or SBE 48 Hull Temperature Sensor.
  • Seasoft for Waves-Win32
    Provides setup, data retrieval, data processing, auto-spectrum and time series analysis, statistics reporting, and plotting for the SBE 26 and SBE 26plus Seagauge Wave & Tide Recorder. Also provides setup, data retrieval, data processing, and plotting for the SBE 53 BPR Bottom Pressure Recorder.

Can I install my Sea-Bird CD-ROM on multiple computers or give it to another interested scientist?

You are free to install the software on multiple computers and to give the software to any interested potential user.

Sea-Bird's Seasoft© software is provided free of charge to Sea-Bird users and is not subject to any license. Seasoft is protected by copyright laws and international copyright treaties, as well as other intellectual property laws and treaties. All title and copyrights in and to Seasoft and the accompanying printed materials, and any copies of Seasoft, are owned by Sea-Bird Electronics. There are no restrictions on its use or distribution, provided such use does not infringe on our copyright.

The software is posted on our website, and anyone can download it.

How can I copy the setup of my Sea-Bird software onto another computer?

A setup file is used by Seasave V7, and by each module in SBE Data Processing, to remember the way you had the program set up. You can save the file to a desired filename and location, and then use it when you run the software the next time, to ensure that the software will be set up the same way:

  • A .psa file is created by Seasave V7 to store program settings, such as the instrument configuration (.con or .xmlcon) file name and path, serial ports, water sampler, TCP/IP ports, serial data output, etc. as well as size, placement, and setup for each display window.
  • A .psa file is created by each  module in SBE Data Processing to store program settings, such as the input filename and path, output filename, and module-specific parameters (for example, for Data Conversion: variables to convert, ascii or binary output, etc.).

If you want to set up real-time acquisition or data processing on more than one computer in the same way, simply copy the file for the desired setup, and transfer it to the other computer via your network, email, a thumb drive, or some other media. Then, after you open the software on the second computer, select the setup file you want to use.

  • Seasave V7: Select File / Open Setup File.
  • SBE Data Processing: In the module dialog box, on the File Setup tab, click the Open button under Program setup file.

How can I view CTD data?

You can plot the raw data from a .dat or .hex file with Seasave V7.

Once the data is converted to a .cnv file with engineering units (using SBE Data Processing’s Data Conversion), you can plot the data in SBE Data Processing’s Sea Plot.

  • Because Sea Plot only works with archived files, it is more sophisticated than Seasave. For example, Sea Plot can provide multiple file overlays, waterfall plots, and TS plots with contours.

If you wish to view the actual numbers you can open the .cnv file (if it was converted as ASCII) with any word processor or text editor.

What is a configuration (.con or .xmlcon) file and how is it used?

The configuration file defines the instrument — auxiliary sensors integrated with the instrument, and channels, serial numbers, and calibration dates and coefficients for all the integrated sensors (conductivity, temperature, and pressure as well as auxiliary sensors). Sea-Bird’s real-time acquisition and data processing software uses the information in the configuration file to interpret and process the raw data (sensor frequencies and voltages). If the configuration file does not match the actual instrument configuration, the software will not be able to interpret and process the data correctly.

When Sea-Bird ships a new instrument, we include a .con or .xmlcon file that reflects the current instrument configuration. The file is named with the instrument serial number, followed with the .con or .xmlcon extension. For example, for an instrument with serial number 2375, Sea-Bird names the .xmlcon file 2375.xmlcon. You may rename the configuration file if desired; this will not affect the results.
(Click here to see an example of where to find the serial number on your instrument)

Seasave V7 and SBE Data Processing version 7.20 (2009) introduced .xmlcon files (in XML format). Versions 7.20 and later allow you to open a .con or .xmlcon file, and to save it to a .con or .xmlcon file.

To view or modify the configuration file, use the Configure Inputs menu in Seasave V7, or the Configure menu in SBE Data Processing.

Notes:

  • Seasave V7 and SBE Data Processing check that the serial number in the configuration file matches the instrument serial number in the .dat or .hex data file. If they are not the same, you will get an error message. The instrument serial number can be verified by sending the Status command (DS or #iiDS, as applicable) in the appropriate terminal program.
  • SBE 16, 16plus, 16plus-IM, 16plus V2, 16plus-IM V2, 19, 19plus, 19plus V2, 21, and 49 — The instrument serial number is the same as the serial number of both the conductivity and temperature sensors.
  • SBE 37 (older), 39, 39plus, and 48 — These instruments store calibration coefficients internally and do not accept auxiliary sensors, so they do not have configuration files.
  • SBE 37 (newer) that is compatible with SeatermV2 terminal program — SeatermV2 creates a configuration file for these instruments when it uploads data. The configuration file can then be used for processing the data in SBE Data Processing.
  • The calibration date in the configuration file is for information only. It does not affect the data processing.
  • When Sea-Bird recalibrates an instrument, we ship the instrument with a Calibration Sheet showing the new calibration coefficients (1 calibration sheet per sensor on the instrument that was calibrated). Sea-Bird also supplies a .xml file with the calibration coefficients for each calibrated sensor. The .xml files can be imported into Seasave or SBE Data Processing, to update the calibration coefficients in the configuration file.
    — For CTDs: Sea-Bird also creates a new configuration file, which includes calibration coefficients for the CTD as well as any auxiliary sensors that were returned to Sea-Bird with the CTD. If you did not return the auxiliary sensors with the CTD, you need to update the configuration file to include information on the auxiliary sensors that you plan to deploy with your CTD.

What is a .psa file and how is it used?

A .psa (program setup) file is used by Seasave V7 and by each module in SBE Data Processing to remember the way you had the program set up. You can save the .psa file to a desired filename and location, and then use it when you run the software the next time, to ensure that the software will be set up the same way:

  • A .psa file is created by Seasave V7 to store program settings, such as the instrument configuration (.con or .xmlcon) file name and path, serial ports, water sampler, TCP/IP ports, serial data output, etc. as well as size, placement, and setup for each display window.
  • A .psa file is created by each  module in SBE Data Processing to store program settings, such as the input filename and path, output filename, and module-specific parameters (for example, for Data Conversion: variables to convert, ascii or binary output, etc.).

If you want to set up real-time acquisition or data processing on more than one computer in the same way, simply copy the .psa file for the desired setup, and transfer it to the other computer via your network, email, a CD-ROM, or some other media. Then, after you open the software on the second computer, select the .psa file you want to use.

  • Seasave V7: Select File / Open Setup File.
  • SBE Data Processing: In the module dialog box, on the File Setup tab, click the Open button under Program setup file.

Does Seasoft have a provision for converting to MatLab data files?

MatLab can import flat ASCII files. To produce those files:

  1. Run SBE Data Processing’s Data Conversion module to produce a .cnv file with data in ASCII engineering units from the raw data file. This file also contains header information.
  2. Run SBE Data Processing’s ASCII Out module to remove the header information, outputting just the data portion of the converted data file to a .asc file. Optionally, you can also output the header information to a .hdr file.

What operating systems are compatible with Seasoft?

Current Sea-Bird software was designed to work on a PC running Windows XP service pack 2 or later, Windows Vista, or Windows 7 (both 32-bit and 64-bit). We chose Windows because of its widespread availability, and suitability as an acquisition platform. Sea-Bird provides the software free of charge as part of our instrument support. Because of this, we do not have the resources to write and provide support software for other operating systems, such as Apple, Unix, or Linux.

  • If you have a valid PC emulator on your system, the Sea-Bird software may run, but we have no way to confirm this, or that the I/O connections to the instrument will properly function.
  • If you have access to a PC running Windows, you can use Sea-Bird’s software to convert the data from our proprietary format to ASCII (in engineering units of C, T, P, etc. with calibration coefficients applied); then you could use your own software on a different computer to perform additional processing.

What is the flag variable column that is added to the data file by SBE Data Processing's Data Conversion or ASCII In module?

The flag variable column is added by Data Conversion (if you process data using Sea-Bird software) or ASCII In (if you are importing data that was generated using other software). The Loop Edit module sets the flag variable to bad for scans that show a pressure slowdown or reversal. The flag variable is then used by the rest of the SBE Data Processing modules as an indication of a bad scan, allowing you to exclude scans that are marked bad from processing performed in a module, if desired.

Initially all scans are marked good (flag value of 0) in Data Conversion or ASCII In. A flag of -9.99e-29 indicates the scan has been marked bad by Loop Edit.

Note: All occurrences of the bad value (-9.99e-29) can be replaced with a different value in ASCII Out. This may be useful for plotting purposes, as -9.99e-29 looks like 0 in a data plot.

How does Sea-Bird software calculate conductivity, temperature, and pressure in engineering units?

For formulas for the calculation of conductivity, temperature, and pressure from the raw data, see the calibration sheets for your instrument. If you cannot find the calibration sheets, contact us with your instrument serial number (Click here to see an example of where to find the serial number on your instrument).

How does Sea-Bird software calculate derived variables such as salinity, sound velocity, density, depth, thermosteric anomaly, specific volume, potential temperature, etc.?

The Seasave and SBE Data Processing manuals document the derived variable formulas in an Appendix (Derived Parameter Formulas). The Help files for these programs also document the formulas. To download the software and/or manuals, go to Software.

What formula does Sea-Bird software use to convert pressure data to depth?

In Sea-Bird software, is noon on January 1 Julian Day 0.5 or Julian Day 1.5?

In Seasoft-DOS version 4.249 and higher (March 2001 and later), January 1 is Julian Day 1. Therefore, noon on January 1 is Julian Day 1.5. Earlier versions of the software incorrectly defined January 1 as Julian Day 0, so noon on January 1 would appear as Julian Day 0.5.

All release versions of SBE Data Processing correctly identify January 1 as Julian Day 1.

Can I edit my .dat data file to add some explanatory notes to the header?

Seasoft V2's Seasave (older software, replaced with Seasave V7 in 2007) created a .dat file from data acquired from the SBE 11plus V2 Deck Unit  / SBE 9plus CTD. This also applies to earlier versions of the Deck Unit and CTD.

Some text editing programs modify the file in ways that are not visible to the user (such as adding or removing carriage returns and line feeds), but that corrupt the format and prevent further processing by Seasoft. Therefore, we strongly recommend that you first convert the data to a .cnv file (using SBE Data Processing's Data Conversion module), and then use other SBE Data Processing modules to edit the .cnv file as desired.

Sea-Bird is not aware of a technique for editing a .dat file that will not corrupt it. 
Sea-Bird distributes a utility program, Fixdat, that may repair a corrupted .dat file. Fixdat.exe is installed with, and located in the same directory as, SBE Data Processing.

Note: Seasave V7 creates a .hex file instead of a .dat file from data acquired from the SBE 11plus V2 Deck Unit / SBE 9plus CTD. See the FAQ on editing a .hex file.

How many/what kind of spares should I have on ship for my instrument?

Very few Sea-Bird instruments completely fail due to component malfunction or manufacturing defects. However, we see a reasonably large number that require repairs of some sort. Most of these are simply due to the user breaking the equipment through rough handling, accidents, or lack of maintenance. It always best to plan for the worst case.

Parts most likely to be damaged are cables, connectors, and sensors (specifically the conductivity cell). Cables and connectors are easily replaced and spares should always be carried. After a sensor is replaced, the instrument must be re-calibrated, so it is really not practical to carry spare cells or temperature probes. If you start carrying many spare boards and sensors you are better off (both in cost and efficiency) having whole spare instruments on board.

Carrying at least 1 complete set of spares, with 3 sets of cables, connectors and dummy plugs, is recommended. How fast you can get spares from shore to the ship should dictate how many spare systems you need to have on board.

Note: See spares recommendations specific to the SBE 9plus.

How will my CTD be affected by adjacent objects?

Sea-Bird’s CTDs are not directly affected by adjacent objects, unlike some CTDs that shift their calibration due to proximity effects. However, the CTD can only measure the water it sees. There are 2 concerns to keep in mind when mounting the CTD:

  • If the CTD is positioned so that the flow of water is blocked or restricted, the CTD will see water that lags behind the true environment. Also, there is a directivity affect in the conductivity measurement: The instrument measures only the conductivity of the water in its conductivity cell. This conductivity cell is oriented along the long axis of the CTD, so it will work better (i.e., get flushed with water representing the true environment) if water can flow along this axis. This is accomplished by orientation of the conductivity cell parallel to the direction of movement and with the use of a pump.
  • The thermal mass of adjacent objects can affect the temperature of the water. If the CTD is near some large object that takes a long time to equilibrate to changing temperature, the temperature of the water in the vicinity will be affected and the CTD will read this affected temperature.

What are the safety concerns/procedures if the instrument floods? Can the instrument explode?

While a CTD leak can result in a dangerous situation, it is not common. Pressure housings may flood under pressure due to dirty or damaged o-rings, or other failed seals, causing highly compressed air to be trapped inside. For example, a housing that floods at 5000 meters depth holds an internal pressure of more than 7000 psia. If this happens, a potentially life-threatening situation can occur when the instrument is brought to the surface. The CTD will not explode. If it does flood and develop pressure inside, the end cap can be shot out of the housing if a technician tries to open the unit without releasing the pressure first.

Possible causes of flooding include:

  • O-rings were not properly prepared or greased after the housing was opened, or
  • Instrument was dropped or hit hard, and a bulkhead connector or the sensor was cracked or damaged.

It is important to visually inspect the instrument for damage before each survey. A cracked bulkhead connector is usually easy to spot.

If the instrument is unresponsive to commands or shows other signs of flooding or damage, see the Recovery section in your instrument manual for details specific to your instrument. For most instruments, follow these precautions:

  1. Every time you open the instrument, loosen each end cap screw a few turns. If the end cap follows the screws out, there is pressure in the housing.
  2. If pressure in the housing is indicated:
    A. Point the instrument in a safe direction away from people.
    B. Loosen 1 of the bulkhead connectors very slowly, at least 1 turn, to release the pressure safely (bulkhead connectors are the black connectors on the end cap, where the cables attach to the instrument). This opens an O-ring seal under the connector. Look for signs of internal pressure (hissing or water leak). If internal pressure is detected, let it bleed off slowly past the connector o-ring. Then, you can safely remove the end cap.

In general, instruments do not flood. However, be aware of the potential for flooding so that if a problem arises you will be able to safely deal with it.

Is it necessary to put my instrument in water to test it? Will I destroy the conductivity cell if I test it in air?

It is not necessary to put the instrument in water to test it. It will not hurt the conductivity cell to be in air.

If there is a pump on the instrument, it should not be run for extended periods in air.

  • Profiling instruments (SBE 9plus, 19, 19plus, 19plus V2, 25, 25plus, 49) and some moored instruments (all pumped MicroCATs with integral dissolved oxygen (DO), and pumped MicroCATs without DO with firmware 3.0 and later) do not turn on the pump unless the conductivity frequency is above a specified minimum value (minimum value is hard-wired in 9plus, user-programmable in other instruments). This prevents the pump from turning on in air. See the instrument manual for details.
  • If your instrument does not check for conductivity frequency before turning on the pump: 
    - For moored SeaCATs (16, 16plus, 16plus-IM, 16plus V2, 16plus-IM V2): Disconnect the pump cable for the test. 
    - For older pumped MicroCATs: orient the MicroCAT to provide an upright U-shape for the plumbing. Then fill the inside of the pump head with water via the pump exhaust tubing; this will provide enough lubrication to prevent pump damage during brief testing.

What are the recommended practices for cleaning and lubricating winch cables?

This topic is covered in detail on the UNOLS (University-National Oceanographic Laboratory System) website; see http://www.unols.org/publications/winch_wire_handbook__3rd_ed/06_wire_rope_em_cable_lub.PDF.

What are the recommended practices for splicing cables?

Sea-Bird typically recommends using the Dam/Blok and EverGrip products from PMI Industries. DamBlok makes the electrical splice and EverGrip provides the strain relief on the cable. See an example of how these products can be used.

For a quick electrical splice in the field using commonly available materials, the UNOLS (University-National Oceanographic Laboratory System) website provides a procedure using hot glue and heat shrink: http://www.unols.org/meetings/2006/200610inm/SessionIV/SessionIV_Rowe_HOT GLUE.pdf. Numerous cycles of deployment to great depths could compromise the seal, but it may be useful for a quick fix.

What is the cause of conductivity drift?

Conductivity cells drift primarily as a function of cell fouling. There are several sources of the fouling:

  • Biological growth is the primary source of cell fouling. Rinsing the conductivity cell with clean de-ionized water after each cast helps prevent most growth in the cell. If the cell is not rinsed, or standard tap water is used, growth rates can be severe. As the cell fouls, it will drift towards lower salinity values.
  • Surface oil slicks also cause cell fouling. Avoid deploying the CTD through obvious slicks. When working in coastal areas, with higher chances of oil fouling, rinse and soak the cell with a 1% Triton X-100 solution (diluted in clean DI water) to help prevent oil fouling.

See Application Note 2D: Instructions for Care and Cleaning of Conductivity Cells for rinsing, cleaning, and storage procedures.

Because of the nature of fouling, the total cell drift may not be linear. It exhibits rapid small shifts (especially if related to oil fouling) on top of a base line drift. It is important to take water samples to document the behavior. Application Note 31: Computing Temperature and Conductivity Slope and Offset Correction Coefficients from Laboratory Calibrations and Salinity Bottle Samples discusses how to correct the data.

Can I use a pressure sensor above its rated pressure?

Digiquartz pressure sensors are used in the SBE 9plus, 53, and 54. The SBE 16plus V2, 16plus-IM V2, 19plus V2, and 26plus can be equipped with either a Druck pressure sensor or a Digiquartz pressure sensor. All other instruments that include pressure use a Druck pressure sensor.

  • The overpressure rating for a Digiquartz (as stated by Paroscientific) is 1.2 * full scale. The sensor will provide data values above 100% of rated full scale; however, Sea-Bird does not calibrate beyond the rated full scale.
  • The overpressure rating for a Druck (as stated by Druck) is 1.5 * full scale. The sensor will provide data values above 100% of rated full scale; however, Sea-Bird does not calibrate beyond the rated full scale.

Note: If you use the instrument above the rated range, you do so at your own risk; the product will not be covered under warranty.

Where can I get information about safe handling/hazards associated with chemicals used with Sea-Bird equipment, such as Anti-Foulant Devices and Triton X-100 detergent?

See Material Safety Data Sheets (MSDS) for chemicals commonly used with Sea-Bird instruments.

What is Triton? Do I need to purchase it from Sea-Bird?

Triton X-100 is Octyl Phenol Ethoxylate, a reagent grade non-ionic surfactant (detergent). Sea-Bird uses it to help keep our conductivity cells clean and the electrodes wetted and ready for immediate use in water (a dry cell requires a few minutes to become completely wetted after immersion). Triton X-100 will not harm conductivity cells, temperature sensors, or pumped fluorometers. Do not place concentrated Triton X-100 directly on the membrane or optical window of a dissolved oxygen sensor.

Triton X-100 is supplied in 100% strength.

Triton X-100 can be ordered from Sea-Bird, but should also be available locally from a chemical supply or laboratory products companies. It is manufactured by Avantor Performance Materials (see http://www.avantormaterials.com/commerce/product.aspx?id=2147509608). See our MSDS page to view the Material Safety Data Sheet.

How do instruments handle external power if internal batteries are installed?

Most Sea-Bird instruments that are designed to be powered internally or externally incorporate diode or'd circuitry, allowing only the voltage that has the greater potential to power the instrument. You can power the instrument externally without running down the internal batteries. This allows you to lab test using external power that has higher voltage than the internal batteries, and then deploy using internal power, knowing that the internal batteries are fresh.

For the SBE 25plus, if external power of 14 volts or higher is applied, the 25plus runs off of the external power, even if the main battery voltage is higher.

What is the maximum cable length for real-time RS-232 data?

Cable length is one of the most misunderstood items in the RS-232 world. The RS-232 standard was originally developed decades ago for a 19200 baud rate, and defines the maximum cable length as 50 feet, or the cable length equal to a capacitance of 2500 pF. The capacitance rule is often forgotten; using a cable with low capacitance allows you to span longer distances without going beyond the limitations of the standard. Also, the maximum cable length mentioned in the standard is based on 19200 baud rate; if baud is reduced by a factor of 2 or 4, the maximum length increases dramatically. Using typical underwater cables, allowable combinations of cable length and baud rate for Sea-Bird instruments communicating with RS-232 are shown below:

Maximum Cable Length (meters) Maximum Baud Rate*
1600 600
800 1200
400 2400
200 4800
100 9600
50 19,200
25 38,400
16 57,600
8 115,200

*Note: Consult instrument manual for baud rates supported for your instrument.

 

When I compute sigma-density values, why are they sometimes negative?

For convenience while examining differences in density between two water parcels, Sigma-density values are typically used by oceanographers. Sigma-density values allow the oceanographer to focus on the last 6 to 7 digits in the density value (when assuming 5 decimal place resolution), as this is where most of the variation in density occurs. Sigma-density values are also a shorthand way for representing density of a water parcel with some specific modification to one of the density computational inputs, like pressure or temperature.

Examples:

  • Sigma = (rho(t,s,p) - 1000) kg/m3
  • Sigma-t = (rho(s,t,p=0) - 1000) kg/m3 (density at atmospheric pressure)
  • Sigma-theta = (rho(t=theta,s,0) - 1000 kg/m3 (density with effect of adiabatic cooling/heating effect [using potential temperature] and the pressure effect removed).


So, though the true density of water is always a value that is non-negative, when testing instruments on the bench (zero salinity) or in freshwater systems, the computed density can be < 1000 kg/m3. In this situation, when converting density to a Sigma-density value, it is possible for the Sigma-density value to be negative.

Example: S = 0, t = 5 deg C, and pressure = 0
rho(S,t,pressure) = 999.96675 kg/m3
Sigma-t (t,S,0) = - 0.03325

For more information on the Practical Salinity Scale (1978) and the Equation of State for Seawater (EOS-80), refer to UNESCO Technical Papers of Marine Science 44.

Note: Many UNESCO marine science publications are available through UNESCO's website. Go to http://unesdoc.unesco.org/ulis/ioc/.

  1. In the Series title box, select UNESCO technical papers in marine science.
  2. Select Widen the search to all UNESCO documents/publications.
  3. Click the OK button.

Why is Teflon tape used?

Adhesive Teflon tape (actually, UHMW tape — Ultra High Molecular Weight polyethylene) provides insulation to prevent damage due to contact of dissimilar metals. It is typically used by Sea-Bird on the inside of hose clamps used for mounting instruments, where U-bolts hold a Carousel Water Sampler frame to an extension stand, etc. The tape can be ordered from Sea-Bird; part number 30409 is 1 inch wide x 0.1 inch thick x 1 foot long (2.5 cm x 0.25 cm x 0.3 m). It can also be purchased from the manufacturer, Crown Plastics (see www.crownplastics.com for local distributors).

What do you recommend for cleaning barnacles off the exterior of the instrument?

Plug the ends of the conductivity cell to prevent the cleaning solution from getting into the cell. Then soak the entire instrument in white vinegar for a few minutes. After scraping off the barnacles and marine growth, rinse the instrument well with fresh water.

We do not advise using hydrochloric acid (HCl) to clean instrument housings. Such highly corrosive acids will not hurt the anodized surfaces, but will attack any bare aluminum — including the aluminum in the cracks — and can also damage O-rings, connectors, and other sensor components.

Note: If sending the instrument to Sea-Bird for calibration, remove as much biological material as possible before shipping. Sea-Bird cannot place an instrument with a large amount of biological material on the housing in our calibration bath; if we need to clean the exterior before calibration, we will charge you for this service.

For minimizing future growth on the housing, completely wrap the instrument housing with plastic tape. The bio-organisms still grow, but after recovery it is easy to peel off the tape, shells and mussels and all!

Can I deploy a Sea-Bird CTD in freshwater, such as a river or lake?

Yes, CTDs are successfully used in many freshwater systems, such as to examine water conditions and vertical density gradients.

It is important to check that the pump on your CTD is enabled for freshwater use. For example, for the SBE 19plus V2, you should change the minimum conductivity frequency setting to enable the pump to turn on at low conductivities. The minimum conductivity frequency should be set to 1 – 5 Hz above the in-air zero raw conductivity frequency for your instrument (see the instrument calibration sheet). For extremely low conductivity systems, such as alpine lakes, you may consider setting the minimum conductivity frequency to 0. It is also important to increase the pump delay to 1 – 2 minutes, to allow enough time for the CTD to reach the water and purge all the air from the plumbing before the pump turns on. See the CTD manual for more details on configuring the pump.

In addition, for profiling CTD applications, note that the cell thermal mass corrections that Sea-Bird uses are intended for seawater. These corrections should not be applied to freshwater data; they can give bad results, due to non-linearity and the way that the derivative dC/dT is calculated in areas where conductivity changes are very small. 

How should I handle my CTD to avoid cracking the conductivity cell?

Shipping: Sea-Bird carefully packs the CTD in foam for shipping. If you are shipping the CTD or conductivity sensor, carefully pack the instrument using the original crate and packing materials, or suitable substitutes.

Use: Cracks at the C-Duct end of the conductivity cell are most often caused by:

  • Hitting the bottom, which can cause the T-C Duct to flex, resulting in cracking at the end of the cell.
  • Removing the soaker tube from the T-C duct in a rough manner, which also causes the T-C Duct to flex. Pulling the soaker tube off at an angle can be especially damaging over time to the cell. Pull the soaker tube off straight down and gently.
  • Improper disassembly of the T-C ducted temperature and conductivity sensors (SBE 25, 25plus, and 9plus) when removing them for shipment to Sea-Bird for calibration. See Shipping SBE 9plus, 25, and 25plus Temperature and Conductivity Sensors for the correct procedure.

Note: If a Tygon tube attached to the conductivity cell has dried out, yellowed, or become difficult to remove, slice (with a razor knife or blade) and peel the tube off of the conductivity cell rather than twisting or pulling the tube off.

What are the pros and cons of ordering wet-pluggable connectors? Can I mate and unmate a cable with this connector underwater?

Wet-pluggable (also referred to as wet-mateable or MCBH) connectors, an option on all of our underwater instruments, may be mated in wet conditions (click here for a photo comparison). Their pins do not need to be dried before mating. By design, water on the connector pins is forced out as the connector is mated. However, they must not be mated or un-mated while submerged. Wet-pluggable connectors have a non-conducting guide pin to assist pin alignment & require less force to mate, making them easier to mate reliably under dark or cold conditions, compared to our Impulse XSG/RMG connectors (XSG/RMG connectors may not seal well in extreme cold; we recommend connecting cables in warm ship’s lab rather than on deck for these conditions). Like XSG/RMG connectors, wet-pluggables need proper lubrication & require care during use to avoid trapping water in sockets.

Wet-pluggable connectors do add additional cost to the instrument. The increase in price is dependent on the number of pins on each connector, and the number of connectors on your instrument. When should you consider configuring your instrument with wet-pluggable connectors? Consider the following guidelines:

  • Internal recording with a profiling CTD (for example, SBE 9plus with 17plus V2, SBE 19plus V2, SBE 25plus) — Connecting/disconnecting frequently to the CTD is typical for these systems, for uploading of the internally recorded data. Wet-pluggable connectors are recommended for these applications.
  • Autonomous water sampling (SBE 32 Carousel with AFM or 17plus V2, or SBE 55 ECO Water Sampler) and internal recording with a profiling CTD — Connecting/disconnecting to the underwater electronics is required after every cast, to re-arm the electronics for autonomous water sampling. Connecting/disconnecting is often done on deck, where the connectors are exposed to splashing and rain; wet-pluggable connectors are strongly recommended for these applications.
  • Real-time data acquisition with a profiling CTD (for example, SBE 9plus with 11plus Deck Unit, SBE 19plus V2 with PDIM and SBE 33 or 36 Deck Unit, SBE 25plus with PDIM and SBE 33 or 36 Deck Unit) — The underwater units in these systems are plugged into the sea cable, and typically are disconnected infrequently. Wet-pluggable connectors are not as important for this application.
  • Moored instruments
    — If data upload after recovery will occur on deck to allow for quick redeployment, wet-pluggable connectors are recommended. 
    — If data upload after recovery will occur in a lab, wet-pluggable connectors are not as important for this application.

Note: Prior to 2005, the wet-pluggable connectors available had a rubber-to-metal seal that could break down with prolonged use (3 - 5 years); seal breakdown will lead to instrument flooding. Sea-Bird recommended frequent inspection of the connectors for damage. We also discouraged the use of wet-pluggable connectors for moored deployments, because they cannot be inspected during a prolonged deployment. 
From 2005 to 2007, Sea-Bird transitioned to the WB (water block) type of wet-pluggable connectors. WB connectors have a water block that minimizes the possibility of instrument flooding; we do not discourage the use of these types of connectors for moored deployments. If you have wet-pluggable connectors on your instrument and are unsure of which type you have, contact Sea-Bird.

Can Sea-Bird provide some guidance for ordering cable, winch, and deck gear?

For a Sea-Bird CTD used with one of our Deck Units (SBE 11plus, SBE 33, or SBE 36), the electrical requirements of the armored cable are simple. Only one conductor is required (the armor is used as ground) and the total 2-way resistance (conductor plus armor) should be under 350 ohms. The mechanical requirements are most driven by the characteristics of the winch and weight of the payload to be lifted. The winch should have a level wind device which is either adjustable or pre-designed to lay the correct number of wraps across the drum, as determined by the cable diameter and drum width. The winch must also be equipped with a slip ring (rotating contact) assembly (at least 2 channels). A cable breaking strength of at least 5 to 7 times the maximum payload weight is recommended for safety and cable longevity. The cable must also be terminated both mechanically and electrically at the underwater (instrument) end. Cable termination (mechanical) at the winch drum is usually addressed by the winch maker. The cable is terminated electrically to the slip ring per the slip ring manufacturer's specification.

Sea-Bird is not expert in winch and deck gear and cannot recommend a block and A-frame. From past experience and with knowledge of what other customers use, we can point out sources for typical cable solutions, and cable terminations suppliers. For links to suppliers of winches, cable, and cable termination hardware, see Third Party Equipment.

How can I tell if the conductivity cell on my CTD is broken?

Conductivity cells are made of glass, which is breakable.

  • If a cell is cracked, it typically causes a salinity shift or erratic data.
  • However, if the crack occurs at the end of the cell, the sensor will continue to function normally until water penetrates the epoxy jacket. Post-cruise calibration results will reveal whether or not water has penetrated the epoxy jacket.

Inspect the cell thoroughly and make sure that it isn’t cracked or abused in any way.

  • (SBE 9plus, 25, or 25plus) If the readings are good at the surface but erratic at depth, it is likely that the problem is in the cable or the connector, not the conductivity cell. Check the connections, making sure that you burp the connectors when you plug them in (see Application Note 57: Connector Care and Cable Installation). Check the cable itself (swap with a spare cable, if available).
  • If the readings are incorrect at the surface but good after a few meters, it is likely that the problem is flow-related. Verify that the pump is working properly. Check the air bleed valve (the white plastic piece in the Y-fitting, which is installed on vertically deployed CTDs) to see if it is clogged; clean out the small hole with a piece of fine wire supplied with your CTD.
  • If the readings are incorrect for the entire cast, there may be an incorrect calibration coefficient or the cell may be cracked.
  • Check the conductivity calibration coefficients in the configuration (.con or .xmlcon) file.
  • Do a frequency check on the conductivity cell. Disconnect the plumbing on the cell. Rinse the cell with distilled or de-ionized water and blow it dry (use your mouth and not compressed air, as there tends to be oil in the air lines on ships). With the cell completely dry, check the frequency reading. It should read within a few tenths of a Hz of the 0 reading on your Calibration Sheet. If it does not, something is wrong with the cell and it needs to be repaired.

What are the major steps involved in taking a cast with a Profiling CTD?

Following is a brief outline of the major steps involved in taking a CTD cast, based on generally accepted practices. However, each ship, crew, and resident technicians have their own operating procedures. Each scientific group has their own goals. Therefore, observe local ship and scientific procedures, particularly in areas of safety. Before the cruise a discussion of the planned work is advisable between the ship’s crew, resident technicians, and scientific party. At this time discuss and clarify any specific ship’s procedures.

Note: The following procedure was written for an SBE 9plus CTD operating with an SBE 11plus Deck Unit. Modify the procedure as necessary for your CTD.

10 to 15 minutes before Station:

  1. Review the next cast’s plan, including proposed maximum cast depth, bottom depth, and number of bottles to close and depths. If the cast will be close to the bottom, familiarize yourself with the bottom topography.
  2. Verify that all water samples have been obtained from the bottles from the previous cast. If so, drain the bottles and cock them. Hand manipulate each Carousel latch as you cock the bottle to ensure it is free to release and is not stuck in some way.
  3. Remove the soaker tubes from the conductivity cells.
  4. Remove any other sensor covers.
  5. With permission from the deck crew, power up the CTD. Check the Deck Unit front panel display to verify communication. Perform a quick frequency check of the main sensors.
  6. Start Seasave. Set up a fixed display. Select Do not archive data for this cast. Start acquisition and view the data to verify the system is operational.
  7. Clean optical sensor windows, and perform any required air calibration.
  8. Stop acquisition. Do Not turn the CTD Deck Unit off. Select begin archiving data immediately. Set up the plot scales and status line.

5 minutes before Station:

  1. Start the ship's depth sounder and obtain a good depth reading. Be careful reading the depth sounder; if it is improperly configured the trace will wrap around the plot and be incorrect. The bottom depth should be close to the expected charted depth.
  2. Fill out any parts of the cast log that can be done at this time.

On Station, On Deck:

  1. Verify the position and the bottom depth.
  2. The computer operator should begin filling out the software header.
  3. After receiving word from the bridge that they are on station and ready to begin, untie the CTD and move it into position. If this requires hydraulics, ensure you have the appropriate people in place and permission.
  4. Position the CTD under the block. Have the winchman remove any slack from the wire.
  5. Notify the computer room that the CTD is ready for launch. The computer room should start acquiring data.
  6. Obtain a barometric pressure reading and note it on the cast sheet.
  7. When the bridge, computer room, and winchman are ready (and you have permission to proceed), put the CTD in the water.
  8. Have the winchman lower the CTD to 10 meters (his readout), hold for 1 minute, and then bring it back to the surface. One operator should remain on deck to help the winchman see when to stop the CTD. The CTD should be far enough below the surface so that the package does not break the surface in the swells.

CTD Soaking at the Surface:

  1. Finish filling out the cast log. Re-check the bottom depth.
  2. Fill out the computer software log.
  3. Hold the CTD at the surface for at least 3 minutes.
  4. Check the status line to verify that the CTD values are correct. The pressure should be the soaking depth of the CTD. Comparing the CTD temperature and salinity to the ship's thermosalinograph is helpful. Log the information (CTD and thermosalinograph) on the cast sheet.

Starting the Cast:

  1. Call the winchman and have him start the cast down. Typical lowering speed is 1 m/sec, modified for conditions as needed.
  2. Watch the computer output and verify that the system is working.

During the Cast:

  1. Closely monitor the CTD output for malfunctions. Sudden noise in a channel is often a sign of a leaking cable. A periodically flashing error light on the Deck Unit is a sign of a bad spot in the slip rings. The modulo error count (usually on the status line) provides an indication of telemetry integrity; on a properly functioning system, there will be no modulo errors.
  2. Note any odd behavior or problems on the cast sheet. Keeping good notes and records is of critical importance. While you may remember what happened an hour from now, in the months that follow, these notes will be a vital link to the cruise as you process the data.
  3. Monitor the bottom depth. This is especially critical if the cast will be close to the bottom, or you are working in an area with varying topography such as in a canyon. Running the CTD into the bottom can cause serious (and expensive) damage.

Approaching the Bottom:

  1. Take extra care if the cast will take the CTD close to the bottom. Monitor the bottom depth, pinger, and altimeter, if available. As you get within 30 meters of the bottom, slow down the cast to 0.5 m/sec. If you wish to get closer than 10 m above the bottom, slow down to 0.2 m/sec. Keep in mind that ship roll will cause the CTD depth to oscillate by several meters.
    - If the CTD does touch bottom, it will be apparent from the sudden, low salinity spike. A transmissometer, if installed, will also show a sudden low spike.
  2. Adjust these numbers and procedures as conditions dictate to avoid crashing the CTD into the bottom.
  3. When the CTD reaches the maximum cast depth, call the winchman and stop the descent.
  4. Log a position on the cast sheet. If a bottle will be closed at the bottom, allow the CTD to soak for at least 1 minute (preferably several minutes) and then close the bottle. Verify that the software records the bottle closure confirmation.
  5. Start the CTD upcast. Stop the CTD ascent at any other bottle closure depths. For each bottle, soak for at least 1 minute (preferably several minutes) and then close the bottle.

End of the Cast:

  1. As the CTD approaches the surface, have someone help spot for the winchman. Stop the CTD below the surface. Close a bottle if desired.
  2. When ready, recover the CTD. Avoid banging the system against the ship.

CTD Back on Board:

  1. Stop data acquisition and power off the CTD.
  2. Move the CTD it into its holding area and secure it.
  3. See Application Note 2D: Instructions for Care and Cleaning of Conductivity Cells for details on rinsing, cleaning, and storing the conductivity cell. Fill the conductivity cell with clean DI (or 1% Triton-X) and secure the filler device to the CTD frame. Freezing water in a conductivity cell will break the cell.
  4. See Application Note 64: SBE 43 Dissolved Oxygen Sensor - Background Information, Deployment Recommendations, and Cleaning and Storage for details on rinsing, cleaning, and storing SBE 43 (membrane-type) dissolved oxygen sensors; see the SBE 63 manual for details on rinsing, cleaning, and storing SBE 63 optical dissolved oxygen sensors.
  5. Rinse any optical sensors.
  6. Rinse the water sampler latches with clean water.
  7. Draw water samples from the bottles.

After the Cast:

  1. Re-plot the data and look at any channels that were not displayed in real time.
  2. Perform diagnostics and take a first pass through processing.
    - Verify that the data is good (at least on a first-order basis) at this point, when you can still re-do the cast. Many casts are lost because they are not analyzed until months later, when the problems are discovered.
  3. Final processing may need to wait until bottle salts and post-cruise lab calibrations are available.

Should I collect water samples (close bottles) on the downcast or the upcast?

Most of our CTD manuals refer to using downcast CTD data to characterize the profile. For typical configurations, downcast CTD data is preferable, because the CTD is oriented so that the intake is seeing new water before the rest of the package causes any mixing or has an effect on water temperature.

However, if you take water samples on the downcast, the pressure on an already closed bottle increases as you continue through the downcast; if there is a small leak, outside water is forced into the bottle, contaminating the sample with deeper water. Conversely, if you take water samples on the upcast, the pressure decreases on an already closed bottle as you bring the package up; any leaking results in water exiting the bottle, leaving the integrity of the sample intact. Therefore, standard practice is to monitor real-time downcast data to determine where to take water samples (locations with well-mixed water and/or with peaks in the parameters of interest), and then take water samples on upcast.

Can I deploy my profiling CTD for monitoring an oil spill?

Sea-Bird CTDs can be deployed in oil; the oil will not cause long-term damage to the CTD. If the oil coats the inside of the conductivity cell and coats the dissolved oxygen sensor membrane, it can possibly affect the sensor’s calibration (and thus affect the measurement and the data). Simple measures can reduce the impact, as follows:

  1. To minimize the ingestion of oil into the conductivity cell and onto the DO sensor membrane:

SBE 19, 19plus, 19plus V2, 25, or 25plus CTD:

Set up the CTD so that the pump does not turn on until the CTD is in the water and below the layer of surface oil, minimizing ingestion of oil (however, some oil will still enter the system). Pump turn-on is controlled by two user-programmable parameters: the minimum conductivity frequency and the pump delay.

Set the minimum conductivity frequency for pump turn-on above the instrument’s zero conductivity raw frequency (shown on the conductivity sensor Calibration Sheet), to prevent the pump from turning on when the CTD is in air. Note that this is the same as our typical recommendation for setting the minimum conductivity frequency.
     For salt water and estuarine applications - typical value = zero conductivity raw frequency + 500 Hz
     For fresh/nearly fresh water - typical value = zero conductivity raw frequency + 5 Hz
If the minimum conductivity frequency is too close to the zero conductivity raw frequency, the pump may turn on when the CTD is in air as result of small drifts in the electronics. Another option is to rely only on the pump turn-on delay time to control the pump; if so, set a minimum conductivity frequency lower than the zero conductivity raw frequency.

Set the pump turn-on delay time to allow enough time for you to lower the CTD below the surface oil layer after the CTD is in the water (the CTD starts counting the pump delay time after the minimum conductivity frequency is exceeded). You may need to set the pump delay time to be longer than our typical 30-60 second recommendation.

The current minimum conductivity frequency and pump delay can be checked by sending the status command to the CTD (DS or GetCD, as applicable). Commands for modifying these parameters are:

  • SBE 19: SP (SBE 19 responds with prompts for setting up these parameters)
  • SBE 19plus and 19plus V2: MinCondFreq=x and PumpDelay=x (where x is the value you are programming).
  • SBE 25: CC (SBE 25 responds with a series of setup prompts, including setting up these parameters)
  • SBE 25plus: SetMinCondFreq=x and SetPumpDelay=x (where x is the value you are programming).

SBE 9plus CTD:

Minimum conductivity frequency and pump delay are not user-programmable for the 9plus. 

If you are using your 9plus with the 11plus Deck Unit, the Deck Unit provides power to the 9plus. Without power, the pump will not turn on. At the start of the deployment, to ensure that you have cleared the surface oil layer before the pump turns on, do not turn on the Deck Unit until the 9plus is below the surface oil layer. Similarly, on the upcast, turn off the Deck Unit before the 9plus reaches the surface oil layer.

If your 9plus is equipped with the optional manual pump control, you can enable manual pump control via the Pump Control tab in Seasave V7’s Configure Inputs dialog box. Once enabled, you can turn the pump on and off from Seasave V7’s Real-Time Control menu. Do not turn the pump on until the CTD is below the surface oil layer. On the upcast, turn the pump off before the CTD reaches the surface oil layer.

  1. To reduce the effect of the ingestion of oil into the conductivity cell and onto the DO sensor membrane or optical window:

After each recovery, rigorously follow the cleaning and storage procedures in the following application notes ‑

  • Application Note 2D: Instructions for Care and Cleaning of Conductivity Cells
  • Application Note 64: SBE 43 Dissolved Oxygen Sensor – Background Information, Deployment Recommendations, and Cleaning and Storage
  • SBE 63 Optical Dissolved Oxygen Sensor manual

Quick Reference Sheets for Oil Spill Deployment:

What are the major steps involved in deploying a moored instrument?

Application Note 83: Deployment of Moored Instruments contains a checklist, which is intended as a guideline to assist you in developing a checklist specific to your operation and instrument setup.

What are the recommended practices for connectors - mating and unmating, cleaning corrosion, and replacing?

Mating and Unmating Connectors:

It is important to prepare and mate connectors correctly, both in terms of the costs to repair them and to preserve data quality. Leaking connectors cause noisy data and even potential system shutdowns. Application Note 57: Connector Care and Cable Installation describes the proper care and installation of connectors for Sea-Bird instruments. The Application Note covers connector cleaning and cable or dummy plug installation, locking sleeve installation, and cold weather tips.

Checking for Leakage and Cleaning Corrosion on Connectors:

If there has been leakage, it will show up as green-colored corrosion product. Performing the following steps can usually reverse the effect of the leak:

  1. Thoroughly clean the connector with water, followed by alcohol.
  2. Give the connector surfaces a light coating of silicon grease.

Re-mate the connectors properly — see Application Note 57: Connector Care and Cable Installation and 9-minute video covering O-ring, connector, and cable maintenance.

Replacing Connectors:

  • The main concern when replacing a bulkhead connector is that the o-rings on the connector and end cap must be prepared and installed correctly; if they are not, the instrument will flood. See the question below for general procedure on handling o-rings.
  • Use a thread-locking compound on the connector threads to prevent the new connector from loosening, which could also lead to flooding.
  • If the cell guard must be removed to open the instrument, take extra care not to break the glass conductivity cell.

What are the recommended practices for inspecting, cleaning, and replacing o-rings?

Inspecting and Cleaning O-Rings and Mating Surfaces:

  1. Remove any water from the o-rings and mating surfaces with a lint-free cloth or tissue.
  2. Visually inspect the o-rings and mating surfaces for dirt, nicks, cuts, scratches, lint, hair, and any signs of corrosion; these could cause the seal to fail. Clean the surfaces, and clean or replace the o-rings as necessary.
  3. Apply a light, even coat of 100% silicon o-ring lubricant (Parker Super O Lube) to the o-rings and mating surfaces. For an end cap o-ring, a ball of lubricant the size of a pea is about all that is needed. Too much lubricant can cause the seal to fail as much, if not more, than no grease. Do not use petroleum-based lubricant (car grease, Vaseline, etc.), as it will cause premature failure of the rubber.
    CAUTION: Parker makes another product, Parker O Lube, that is petroleum-based. Do not use this product; verify that you are using Parker Super O Lube.
  4. After lubricating the o-ring, immediately reassemble the end cap or connector, verifying that no hairs or lint have collected on the lubricated o-ring.

Replacing O-Rings:

  • End Cap O-Rings: We recommend scheduled replacement of end cap o-rings approximately every 3 years, to prevent leaks caused by normal o-ring wear.
  • Connector O-Rings: Replacing connector o-rings requires de-soldering and re-soldering the connector wires, which makes it a more difficult task. Therefore, we recommend replacement of connector o-rings when needed, not on a routine, scheduled basis.

Additional Information:

  • 9-minute video covering O-ring, connector, and cable maintenance.
  • Short, silent video of application of lubricant to o-ring.
  • Short, silent video of application of lubricant to o-ring mating surface (note the use of a plastic dental syringe — no sharp points to scratch the housing — to apply the lubricant).

What is an Anti-Foulant Device? Does it affect the conductivity cell calibration? How often should I replace it? Does it require special handling?

The Anti-Foulant Device is an expendable device that is installed on each end of the conductivity cell, so that any water that enters the cell is treated. Anti-Foulant Devices are typically used with moored instruments (SBE 16, 16plus, 16plus-IM, 16plus V2, 16plus-IM V2, 37-SM, 37-SMP, 37-SMP-IDO, 37-SMP-ODO, 37-SI, 37-SIP, 37-SIP-IDO, 37-IM, 37-IMP, 37-IMP-IDO, 37-IMP-ODO), thermosalinographs (SBE 21 and 45), glider CTDs (Glider Payload CTD), moored profilers (SBE 52-MP), and drifters (SBE 41/41CP Argo float CTDs), and optionally with SBE 19plus, 19plus V2, and 49 profilers.

Anti-Foulant Devices have no effect on the calibration, because they do not affect the geometry of the conductivity cell in any way. The Anti-Foulant Devices are mounted at either end of the conductivity cell. For an in-depth explanation of how Sea-Bird makes the conductivity measurement, see Conductivity Sensors for Moored and Autonomous Operation.

Useful deployment life varies, depending on several factors. We recommend that customers consider more frequent anti-foulant replacement when high biological activity and strong current flow (greater dilution of the anti-foulant concentration) are present. Moored instruments in high growth and strong dilution environments have been known to obtain a few months of quality data, while drifters that operate in non-photic, less turbid deep ocean environments may achieve years of quality data. Experience may be the strongest determining factor in specific deployment environments. Sea-Bird recommends that you keep track of how long the devices have been deployed, to allow you to purchase and replace the devices when needed.

Note that the anti-foulant device does not actually dissolve, so there is no way to visually determine if the anti-foulant device is still effective.

The cost of the anti-foulant devices is small compared to the deployment costs, so we recommend that you replace the devices before each deployment. This will provide the maximum bio-fouling protection, resulting in long-term data quality. 

Shelf Life and Storage: The best way to store Anti-Foulant Devices is in an air-tight, opaque container. The rate of release of anti-foulant is based on saturation of the environment. The anti-foulant will release until the environment is fully saturated (100% saturated) and then it will no longer release any anti-foulant. So if you keep Anti-Foulant Devices sealed well in an air-tight container, theoretically they will stay good for extended periods of time. Exposure to direct sunlight can also affect the release of anti-foulant; we recommend storage in an opaque container.

Handling:

  • For details, refer to the Material Safety Data Sheet, enclosed with the shipment and available on our MSDS page.
  • Anti-Foulant Devices are not classified by the U.S. DOT or the IATA as hazardous material.

What are the recommended practices for storing sensors at low temperatures, and deploying at low temperatures or in frazil or pancake ice?

General

Large numbers of Sea-Bird conductivity instruments have been used in Arctic and Antarctic programs.

Special accommodation to keep temperature, conductivity, oxygen, and optical sensors at or above 0 C is advised. Often, the CTD is brought inside protective doors between casts to achieve this.

Conductivity Cell

When freezing is possible, we recommend that the conductivity sensor be stored dry. Remove larger droplets of water by blowing through the cell. Do not use compressed air, which typically contains oil vapor. Attach a length of Tygon tubing to each end of the conductivity cell to close the cell ends. See Application Note 2D: Instructions for Care and Cleaning of Conductivity Cells for details.

There are several considerations to weigh when contemplating deployments at low temperatures in general, and in frazil or pancake ice:

  • Ensure that the instrument is at or above water temperature before it is deployed. If the cell gets colder than 0 to -2 ºC while on deck, when it enters the water a layer of ice forms inside the cell as the cell warms to ocean temperature. If ice forms inside the conductivity cell, measurements will be low of correct until the ice layer melts and disappears. Thin layers of ice will not hurt the conductivity cell, but repeated ice formation on the electrodes will degrade the conductivity calibration (at levels of 0.001 to 0.020 psu) and thicker layers of ice can lead to glass fracture and permanent damage of the cell.
  • For accurate measurements, keep ice out of the sensing region of the conductivity cell. The conductivity measurement involves determining the electrical resistance of the water inside the sensor. Ice is essentially a non-conductor. To the extent that ice displaces the water, the conductivity will register (very) misleadingly low. Some type of screening is necessary to keep ice out of the cell. This is relatively easy to arrange for the Sea-Bird conductivity cell, which is an electrode-type cell, because its sensing region is totally inside a long tube; plastic mesh could be positioned at each end and would have zero effect on accuracy and stability.

The above considerations apply to all known conductivity sensor types, whether electrode or inductive types. 

If deploying at low temperatures but no surface frazil or pancake ice is present, rinse the conductivity cell in one of the following salty solutions (salty water depresses the freezing point) to prevent freezing during deployment. But this does not mean you can store the cell in one of these solutions outside . . . it will freeze.

  • Solution of 1% Triton in sterile seawater (use 0.5-micron filtered seawater or boiled seawater),   or
  • Brine solution (distilled seawater or homemade salt solution that is higher than 35 psu in salinity).

Note that there is still a risk of forming ice inside the conductivity cell if deploying through frazil or pancake ice on the surface, if the freezing point of the salt water is the same as the water temperature. Therefore, we recommend that you deploy the conductivity cell in a dry state for these deployments.

Commercially available alcohol or glycol antifreezes contain trace amounts of oils that will coat the conductivity cell and the electrodes, causing a calibration shift, and consequently result in errors in the data. Do not use alcohol or glycol in the conductivity cell.

Temperature Sensor

In general, neither the accuracy of the temperature measurement nor the survival of the temperature sensor will be affected by ice.

Oxygen Sensor

For the SBE 43 and SBE 63 Dissolved Oxygen sensor, avoid prolonged exposure to freezing temperature, including during shipment. Do not store the with water (fresh or seawater), Triton solution, alcohol, or glycol in the plenum. The best precaution is to keep the sensor indoors or in some shelter out of the cold weather.

How many/what kind of spares should I have on ship for my SBE 9plus?

The most complete backup system would be another SBE 9plus, to allow for very rapid system swaps. This is important if your stations are close together and there is limited time between CTD casts. However, it is the most expensive option.

The next step down would be an SBE 9plus without sensors. In this case, a system failure would require swapping sensors and pumps to the new unit. This is not difficult, but it is somewhat time consuming. If you have several hours between casts it should not be a problem.

The next option would be to carry spare boards and try and troubleshoot the problem and replace boards. If you have a technician that can do this it is not a bad option. However, it requires some clean and dry lab space to open the CTD and work. You will also have to properly re-seal the CTD. Based upon experience, the SBE 9plus does not fail very often. The most common failure is the main DC-to-DC converter. Other than that, there are very few system failures. However, there are several components that can be damaged through mistakes or misuse. The most catastrophic, other that losing the whole CTD, is to plug the sea cable into the bottom contact connector on the bottom end cap; if this happens, several circuit boards will be destroyed (Note: In 2007 Sea-Bird began using a female bulkhead connector on the 9plus for the bottom contact switch, to differentiate from the sea cable connector and prevent this error. If desired, older CTDs can be retrofitted with the female connector.).

If the budget allows it, we recommend getting a complete backup SBE 9plus, including sensors. If there is any problem, return the malfunctioning instrument for repair and continue sampling with the spare instrument. A complete backup also provides you with spare sensors, so you can rotate 1 set through calibration and continue to operate.

Does it matter if I deploy my moored instrument, which includes a conductivity sensor, in a horizontal or vertical position?

Yes, vertical is usually preferable. In the presence of consistent currents and suspended sediment, we have seen instances where a horizontal conductivity cell is scoured by the abrasive effect of the flow. When scouring is particularly intense, the electrodes can be stripped of their electroplated platinum-black coating, driving the calibration toward fresher readings. Sedimentation (silting) in the cell also drives the readings fresh of correct.

Mounting the instrument vertically avoids abrasive flow and sediment build-up while allowing wave motions and Bernoulli pressures to flush the cell.

Note that some moored sensors (SBE 37-SIP37-SIP-IDO, 37-SMP37-SMP-IDO37-SMP-ODO37-IMP37-IMP-IDO37-IMP-ODO) have a recommended orientation because of their u-shaped plumbing configuration. Refer to the instrument manual for details.

Does Sea-Bird have any calibration/service centers outside of the United States?

Sea-Bird opened a calibration/service center in Kempten, Germany in 2011, providing duty-free servicing for EU customers. The dedicated technical support staff and calibration technicians were extensively trained by Sea-Bird experts. Calibration cross-referencing between the US and Germany facilities ensures Sea-Bird factory quality and accuracy. The German facility stocks a full range of parts and supplies to support repairs. Details.

What are the recommended practices for inspecting, cleaning, and replacing o-rings?

Inspecting and Cleaning O-Rings and Mating Surfaces:

  1. Remove any water from the o-rings and mating surfaces with a lint-free cloth or tissue.
  2. Visually inspect the o-rings and mating surfaces for dirt, nicks, cuts, scratches, lint, hair, and any signs of corrosion; these could cause the seal to fail. Clean the surfaces, and clean or replace the o-rings as necessary.
  3. Apply a light, even coat of 100% silicon o-ring lubricant (Parker Super O Lube) to the o-rings and mating surfaces. For an end cap o-ring, a ball of lubricant the size of a pea is about all that is needed. Too much lubricant can cause the seal to fail as much, if not more, than no grease. Do not use petroleum-based lubricant (car grease, Vaseline, etc.), as it will cause premature failure of the rubber.
    CAUTION: Parker makes another product, Parker O Lube, that is petroleum-based. Do not use this product; verify that you are using Parker Super O Lube.
  4. After lubricating the o-ring, immediately reassemble the end cap or connector, verifying that no hairs or lint have collected on the lubricated o-ring.

Replacing O-Rings:

  • End Cap O-Rings: We recommend scheduled replacement of end cap o-rings approximately every 3 years, to prevent leaks caused by normal o-ring wear.
  • Connector O-Rings: Replacing connector o-rings requires de-soldering and re-soldering the connector wires, which makes it a more difficult task. Therefore, we recommend replacement of connector o-rings when needed, not on a routine, scheduled basis.

Additional Information:

  • 9-minute video covering O-ring, connector, and cable maintenance.
  • Short, silent video of application of lubricant to o-ring.
  • Short, silent video of application of lubricant to o-ring mating surface (note the use of a plastic dental syringe — no sharp points to scratch the housing — to apply the lubricant).

What is an Anti-Foulant Device? Does it affect the conductivity cell calibration? How often should I replace it? Does it require special handling?

The Anti-Foulant Device is an expendable device that is installed on each end of the conductivity cell, so that any water that enters the cell is treated. Anti-Foulant Devices are typically used with moored instruments (SBE 16, 16plus, 16plus-IM, 16plus V2, 16plus-IM V2, 37-SM, 37-SMP, 37-SMP-IDO, 37-SMP-ODO, 37-SI, 37-SIP, 37-SIP-IDO, 37-IM, 37-IMP, 37-IMP-IDO, 37-IMP-ODO), thermosalinographs (SBE 21 and 45), glider CTDs (Glider Payload CTD), moored profilers (SBE 52-MP), and drifters (SBE 41/41CP Argo float CTDs), and optionally with SBE 19plus, 19plus V2, and 49 profilers.

Anti-Foulant Devices have no effect on the calibration, because they do not affect the geometry of the conductivity cell in any way. The Anti-Foulant Devices are mounted at either end of the conductivity cell. For an in-depth explanation of how Sea-Bird makes the conductivity measurement, see Conductivity Sensors for Moored and Autonomous Operation.

Useful deployment life varies, depending on several factors. We recommend that customers consider more frequent anti-foulant replacement when high biological activity and strong current flow (greater dilution of the anti-foulant concentration) are present. Moored instruments in high growth and strong dilution environments have been known to obtain a few months of quality data, while drifters that operate in non-photic, less turbid deep ocean environments may achieve years of quality data. Experience may be the strongest determining factor in specific deployment environments. Sea-Bird recommends that you keep track of how long the devices have been deployed, to allow you to purchase and replace the devices when needed.

Note that the anti-foulant device does not actually dissolve, so there is no way to visually determine if the anti-foulant device is still effective.

The cost of the anti-foulant devices is small compared to the deployment costs, so we recommend that you replace the devices before each deployment. This will provide the maximum bio-fouling protection, resulting in long-term data quality. 

Shelf Life and Storage: The best way to store Anti-Foulant Devices is in an air-tight, opaque container. The rate of release of anti-foulant is based on saturation of the environment. The anti-foulant will release until the environment is fully saturated (100% saturated) and then it will no longer release any anti-foulant. So if you keep Anti-Foulant Devices sealed well in an air-tight container, theoretically they will stay good for extended periods of time. Exposure to direct sunlight can also affect the release of anti-foulant; we recommend storage in an opaque container.

Handling:

  • For details, refer to the Material Safety Data Sheet, enclosed with the shipment and available on our MSDS page.
  • Anti-Foulant Devices are not classified by the U.S. DOT or the IATA as hazardous material.

Does it matter whether you use natural or artificial seawater for calibrations? Which does Sea-Bird use?

For SBE 4 conductivity calibrations, Sea-Bird uses natural seawater that has been carefully collected, stored, UV irradiated, and filtered. Artificial seawater is not adequate if calibration errors are to be kept below 0.010 psu.
Note: SBE 4 is the conductivity sensor in the SBE 9plus, 25, and 25plus profiling CTDs.

The primary difference between natural and artificial seawater is the behavior of conductivity versus temperature. The practical salinity scale 1978 equations include a term rt. This term is expanded into a fourth order equation that describes the variation of conductivity versus temperature for a sample of constant salinity. The equation’s coefficients are derived by fitting to natural seawater samples. Artificial seawater does not have the same conductivity versus temperature characteristic, providing incorrect coefficients and causing a slope error in the calibration.

For calibrations of conductivity sensors other than the SBE 4, Sea-Bird uses artificial seawater (NaCl solution). However, we place an SBE 4 conductivity sensor in each bath, providing a standard for reference to the natural seawater calibration. This allows us to correct errors in the coefficients and slope introduced with the artificial seawater calibration.

For calibration of temperature sensors, Sea-Bird uses artificial seawater (NaCl solution).

Do you recommend a particular brand of alkaline D-cell batteries?

For Sea-Bird instruments that use alkaline D-cells, Sea-Bird uses Duracell MN 1300, LR20. While rare, we have seen a few problems with cheaper batteries over the years: they are more likely to leak, may vary in size (leading to loose batteries causing a bad power connection), and may not last as long.

Why is Teflon tape used?

Adhesive Teflon tape (actually, UHMW tape — Ultra High Molecular Weight polyethylene) provides insulation to prevent damage due to contact of dissimilar metals. It is typically used by Sea-Bird on the inside of hose clamps used for mounting instruments, where U-bolts hold a Carousel Water Sampler frame to an extension stand, etc. The tape can be ordered from Sea-Bird; part number 30409 is 1 inch wide x 0.1 inch thick x 1 foot long (2.5 cm x 0.25 cm x 0.3 m). It can also be purchased from the manufacturer, Crown Plastics (see www.crownplastics.com for local distributors).

What do you recommend for cleaning barnacles off the exterior of the instrument?

Plug the ends of the conductivity cell to prevent the cleaning solution from getting into the cell. Then soak the entire instrument in white vinegar for a few minutes. After scraping off the barnacles and marine growth, rinse the instrument well with fresh water.

We do not advise using hydrochloric acid (HCl) to clean instrument housings. Such highly corrosive acids will not hurt the anodized surfaces, but will attack any bare aluminum — including the aluminum in the cracks — and can also damage O-rings, connectors, and other sensor components.

Note: If sending the instrument to Sea-Bird for calibration, remove as much biological material as possible before shipping. Sea-Bird cannot place an instrument with a large amount of biological material on the housing in our calibration bath; if we need to clean the exterior before calibration, we will charge you for this service.

For minimizing future growth on the housing, completely wrap the instrument housing with plastic tape. The bio-organisms still grow, but after recovery it is easy to peel off the tape, shells and mussels and all!

Why is the color on my instrument housing changing? Does it need to be repaired?

The housings of some of our instrument are made from anodized aluminum. In our experience it is very common to see color change when anodized housings are moored in seawater. We even see some discoloration during the brief time instruments undergo calibration and testing.

There may be several causes of discoloration:

  • Zinc from the protective anodes tends to deposit on the surface, causing the color to lighten toward gray.
  • Some seawater components, for example, carbonates, may precipitate onto the surfaces.
  • The anodized coating does not completely cover the aluminum: at microscopic scale the coating has the appearance of a dry lake bed ‑ there are patches of anodizing surrounded by cracks. These cracks allow water to reach bare aluminum and cause local oxidation that is light in color. Fortunately, once a thin oxide coating forms on aluminum, further corrosion tends to be inhibited. Unless you see severe pitting, there is usually no danger to the safety of the housing.

Can I get my CTD calibrated in the low conductivity range for use in freshwater only?

No, Sea-Bird does not perform low or narrow range calibrations on our CTDs. However, CTDs are used successfully in many freshwater environments.

Conductivity calibrations performed at Sea-Bird are valid in the range of 0 – 9 S/m (or 0 – 7 S/m, as specified for some instruments), and the calibration coefficients can be applied in freshwater for accurate calculations of conductivity.

Sea-Bird recognizes that calibration using natural seawater and IAPSO standards for ocean conductivity ranges may result in a small offset and possible slope errors near zero conductivity. For example, the estimated magnitude of offset error is < 0.002 S/m, and of slope error is < 0.002 S/m per 1 S/m change. This is an example of a conservative error estimate for initial accuracy of conductivity sensors used in freshwater, which can be challenging to calculate due to lack of a freshwater standard. However, sensor precision will be near the resolution (0.00004 S/m). Sea-Bird CTDs provide high precision and sensor stability, allowing an accurate measure of conductivity gradients (dC/dz) or water sample differences, regardless of ‘true’ conductivity values.  For these reasons, Sea-Bird CTDs that have been calibrated in seawater can be used successfully in many freshwater systems.

Lastly, note that the Practical Salinity Scale (PSS-78) is defined as valid for salinity ranges from 2 – 42 PSU. For additional references on freshwater algorithms used in the limnology field, see the following literature:

  • Millero, Frank J. 2000. Equation of State for Freshwater. Aquatic Geochemistry, 6: 1 – 17.
  • Pawlowicz, R. 2008. Calculating the Conductivity of Natural Waters. L&O: Methods 6, 489 – 501.  

How should I handle my CTD to avoid cracking the conductivity cell?

Shipping: Sea-Bird carefully packs the CTD in foam for shipping. If you are shipping the CTD or conductivity sensor, carefully pack the instrument using the original crate and packing materials, or suitable substitutes.

Use: Cracks at the C-Duct end of the conductivity cell are most often caused by:

  • Hitting the bottom, which can cause the T-C Duct to flex, resulting in cracking at the end of the cell.
  • Removing the soaker tube from the T-C duct in a rough manner, which also causes the T-C Duct to flex. Pulling the soaker tube off at an angle can be especially damaging over time to the cell. Pull the soaker tube off straight down and gently.
  • Improper disassembly of the T-C ducted temperature and conductivity sensors (SBE 25, 25plus, and 9plus) when removing them for shipment to Sea-Bird for calibration. See Shipping SBE 9plus, 25, and 25plus Temperature and Conductivity Sensors for the correct procedure.

Note: If a Tygon tube attached to the conductivity cell has dried out, yellowed, or become difficult to remove, slice (with a razor knife or blade) and peel the tube off of the conductivity cell rather than twisting or pulling the tube off.

How often do I need to have my instrument and/or auxiliary sensors recalibrated? Can I recalibrate them myself?

General recommendations:

  • Profiling CTD — recalibrate once/year, but possibly less often if used only occasionally. We recommend that you return the CTD to Sea-Bird for recalibration. (In principle, it is possible for calibration to be performed elsewhere, if the calibration facility has the appropriate equipment andtraining. However, the necessary equipment is quite expensive to buy and maintain.) In between laboratory calibrations, take field salinity samples to document conductivity cell drift.
  • Thermosalinograph — recalibrate at least once/year, but possibly more often depending on the degree of bio-fouling in the water.
  • DO sensor —
    — SBE 43 — recalibrate once/year, but possibly less often if used only occasionally and stored correctly (see Application Note 64), and also depending on the amount of fouling and your ability to do some simple validations (see Application Note 64-2)
    — SBE 63 — recalibrate once/year, but possibly less often if used only occasionally and stored correctly and also depending on the amount of fouling and your ability to do some simple validations (see SBE 63 manual)
  • pH sensor —
    — SBE 18 pH sensor or SBE 27 pH/ORP sensor — recalibrate at the start of every cruise, and then at least once/month, depending on use and storage
    — Satlantic SeaFET pH sensor — recalibrate at least once/year. See FAQ tab on Satlantic's SeaFET page for details (How often does the SeaFET need to be calibrated?).
  • Transmissometer — usually do not require recalibration for several years. Recalibration at the manufacturer’s factory is the most practical method.

Profiling CTDs:

We often have requests from customers to have some way to know if the CTD is out of calibration. The general character of sensor drift in Sea-Bird conductivity, temperature, and pressure measurements is well known and predictable. However, it is very difficult to know precisely how far a CTD calibration has drifted over time unless you have access to a very sophisticated calibration lab. In our experience, an annual calibration schedule will usually maintain the CTD accuracy to within 0.01 psu in Salinity.

Conductivity drifts as a change in slope as a result of accumulated fouling that coats the inside of the conductivity cell, reducing the area of the cell and causing an under-reporting of conductivity. Fouling consists of both biological growth and accumulated oils and inorganic material (sediment). Approximately 95% of fouling occurs as the cell passes through oil and other contaminants floating on the sea surface. Most conductivity fouling is episodic, as opposed to gradual and steady drift. Most fouling events are small and mostly transitory, but they have a cumulative affect over time. A severe fouling event, such as deployment through an oil spill, could have a dramatic but only partially recoverable effect, causing an immediate jump shift toward lower salinity. As fouling becomes more severe, the fit becomes increasingly non-linear and offsets and slopes no longer produce adequate correction, and return to Sea-Bird for factory calibration is required. Frequently checking conductivity drift is likely to be the most productive data assurance measure you can take. Comparing conductivity from profile to profile (as a routine check) will allow you to detect sudden changes that may indicate a fouling event and the need for cleaning and/or re-calibration.

Temperature generally drifts slowly, at a steady rate and predictably as a simple offset at the rate of about 1-2 millidegrees per year. This is approximately equal to 1-2 parts per million in Salinity error (very small).

Pressure sensor drift is also an offset, and annual comparisons to an accurate barometer to determine offset will generally keep the sensor within specification for several years, particularly as the sensors age over time.

I am planning to ship my instrument to Sea-Bird for calibration and minor repairs. What is the typical turn-around time?

Typically, Sea-Bird can calibrate the instrument and perform minor repairs within 3 - 4 weeks, plus shipping time. However, this may vary, depending on current backlog. Before shipping an instrument to us, go to our Online RMA and Service Request Form page to obtain an RMA number, so that we know your instrument is on the way and can schedule appropriately. If time is critical, contact us before shipping to verify that we can meet your schedule.

Notes:

I am planning to ship my instrument to Sea-Bird for calibration and minor repairs. Should I also send the auxiliary sensors from other manufacturers?

The answer to this question depends on your budget and your level of confidence that the entire system is functioning properly. When Sea-Bird receives CTDs that have integrated auxiliary sensors produced by other manufacturers, we test the functionality of the entire system. For a standard charge, we:

  • Visually inspect the physical condition of the auxiliary sensor, connector, and interface cable.
  • Visually inspect the mounting scheme of the auxiliary sensor on the CTD (a poor mounting scheme can result in poor data).*
  • (For voltage sensors) Measure the open voltage and block voltage to ensure that the auxiliary sensor responds through the full 0 - 5V range.
  • Check that the auxiliary sensor reads correctly when submerged in our cold salt water test baths for 30 - 60 minutes.

If the auxiliary sensor does not meet our standards*, we recommend that the sensor be sent to the other manufacturer for service. If the sensor is sent to the other manufacturer, we perform the same tests when it returns to us after servicing. Additionally, we update the configuration (.con or .xmlcon) file with any new calibration coefficients.

*Note: Sea-Bird can fix mounting scheme issues; we do not send the sensor to the other manufacturer for this.

My auxiliary sensor (not manufactured by Sea-Bird) needs to be repaired / recalibrated. Where should I send it for servicing?

Sea-Bird does not repair or recalibrate other manufacturers’ instruments that have been integrated with Sea-Bird equipment. If an auxiliary sensor needs to be repaired or recalibrated, we recommend that you send it directly to the manufacturer. If you send it to Sea-Bird, we will have to send it to the manufacturer, resulting in additional shipping (and possibly customs) expenses for you.

Note: Apparent malfunctioning of an auxiliary sensor can be caused by many things, including incorrect configuration (.con or .xmlcon) file, incorrect instrument setup, incorrect or leaky cables, poor mounting scheme, etc.

  • If you are not certain that the auxiliary sensor needs to be repaired, Sea-Bird can help you troubleshoot the system by phone or e-mail at no charge.
  • Alternatively, if you ship us the entire system, we can troubleshoot at the factory for our standard charges (see the FAQ above this for troubleshooting description). If we determine that the auxiliary sensor does need to be repaired, we will coordinate with you on shipment of the sensor to the manufacturer.

I want to add an auxiliary sensor to my CTD (SBE 9plus, 16, 16plus, 16plus-IM, 16plus V2, 16plus-IM V2, 19, 19plus, 19plus V2, 21, 25, or 25plus). Assuming the auxiliary sensor is compatible with the instrument, what is the procedure?

Adding the sensor(s) is reasonably straightforward:

  1. Mount the sensor; a poor mounting scheme can result in poor data.
    Note: If the new sensor will be part of a pumped system, the existing plumbing must be modified; consult Sea-Bird for details.
  2. Attach the new cable.
  3. (not applicable to 9plus used with 11plus Deck Unit) Using the appropriate terminal program — Enable the channel(s) in the CTD, using the appropriate instrument command.
  4. Using Seasave V7 or SBE Data Processing — Modify the CTD configuration (.con or .xmlcon) file to reflect the new sensor, and type in the calibration coefficients.

Do I need to remove batteries before shipping my instrument for a deployment or to Sea-Bird?

Alkaline batteries can be shipped installed in the instrument. See Shipping Batteries for information on shipping instruments with Lithium or Nickel-Metal Hydride (NiMH) batteries.

I want to change the pressure sensor on my CTD, swapping it as needed to get the best data for a given deployment depth. Can I do this myself, or do I need to send the instrument to Sea-Bird?

On most of our instruments, replacement of the pressure sensor should be performed at Sea-Bird. We cannot extend warranty coverage if you replace the pressure sensor yourself.

However, we recognize that you might decide to go ahead and do it yourself because of scheduling/cost issues. Some guidelines follow:

  1. Perform the swap and carefully store the loose sensor on shore in a laboratory or electronics shop environment, not on a ship. The pressure sensor is fairly sensitive to shock, and a loose sensor needs to be stored carefully. Dropping the sensor will break it.
  2. Some soldering and unsoldering is required. Verify that the pressure sensor is mounted properly in your instrument. Properly re-grease and install the o-rings, or the instrument will flood.
  3. Once the sensor is installed, back-fill it with oil. Sea-Bird uses a vacuum-back filling apparatus that makes this job fairly easy. We can provide a drawing showing the general design of the apparatus, which can be modified and constructed by your engineers.
  4. For the most demanding work, calibrate the sensor on a deadweight tester to ensure proper operation and calibration.
  5. Enter the calibration coefficients for the new sensor in:
  • the CTD configuration (.con or .xmlcon) file, using Seasave V7 or SBE Data Processing, and
  • (for an instrument with internally stored calibration coefficients) the CTD EEPROM, using the appropriate terminal program and the appropriate calibration coefficient commands

Note: This discussion does not apply to the SBE 25 (not 25plus), which uses a modular pressure sensor (SBE 29) mounted externally on the CTD. Swap the SBE 29 as desired, use the CC command in Seaterm or SeatermAF to enter the new pressure range and pressure temperature compensation value, and type the calibration coefficients for the new sensor into the CTD configuration (.con or .xmlcon) file in Seasave V7 or SBE Data Processing.

Can I brush-clean and replatinize the conductivity cell myself? How often should this be done?

Brush-cleaning and replatinizing should be performed at Sea-Bird. We cannot extend warranty coverage if you perform this work yourself.

The brush-cleaning and replatinizing process requires specialized equipment and chemicals, and the disassembly of the sensor. If performed incorrectly, you can damage the cell. Additionally, the sensor must be re-calibrated when the work is complete.

Sea-Bird determines whether brush-cleaning and replatinizing is required based upon how far the calibration has drifted from the original calibration. Typically, a conductivity sensor on a profiling CTD requires brush-cleaning and replatinizing every 5 years.

I sent my conductivity sensor to Sea-Bird for calibration, and you also performed a Cleaning and Replatinizing (C &P). You sent the instrument back with 2 sets of calibration data. What does this mean?

The post-cruise calibration contains important information for drift calculations. The post-cruise calibration is performed on the cell as we received it from you, and is an indicator of how much the sensor has drifted in the field. Information from the post-cruise calibration can be used to adjust your data, based on the sensor’s drift over time. See Application Note 31: Computing Temperature and Conductivity Slope and Offset Correction Coefficients from Laboratory Calibrations and Salinity Bottle Samples.

If the sensor has drifted significantly (based on the data from the post-cruise calibration), Sea-Bird performs a C & P to restore the cell to a state similar to the original calibration. After the C & P, the sensor is calibrated again. This calibration serves as the starting point for future data, and for the sensor’s next drift calculation.

The C & P tends to return the cell to its original state. However, there are many subtle factors that may result in the post-C & P calibration not exactly matching the original calibration. Basically, the old platinizing is stripped off and new platinizing is plated on. Anything in this process that alters the cell slightly will result in a difference from the original calibration. We compare the calibration after C & P with the original calibration, not to make any drift analysis, but to make sure we did not drastically alter the cell, or that the cell was not damaged during the C & P process.

How can I tell if the conductivity cell on my CTD is broken?

Conductivity cells are made of glass, which is breakable.

  • If a cell is cracked, it typically causes a salinity shift or erratic data.
  • However, if the crack occurs at the end of the cell, the sensor will continue to function normally until water penetrates the epoxy jacket. Post-cruise calibration results will reveal whether or not water has penetrated the epoxy jacket.

Inspect the cell thoroughly and make sure that it isn’t cracked or abused in any way.

  • (SBE 9plus, 25, or 25plus) If the readings are good at the surface but erratic at depth, it is likely that the problem is in the cable or the connector, not the conductivity cell. Check the connections, making sure that you burp the connectors when you plug them in (see Application Note 57: Connector Care and Cable Installation). Check the cable itself (swap with a spare cable, if available).
  • If the readings are incorrect at the surface but good after a few meters, it is likely that the problem is flow-related. Verify that the pump is working properly. Check the air bleed valve (the white plastic piece in the Y-fitting, which is installed on vertically deployed CTDs) to see if it is clogged; clean out the small hole with a piece of fine wire supplied with your CTD.
  • If the readings are incorrect for the entire cast, there may be an incorrect calibration coefficient or the cell may be cracked.
  • Check the conductivity calibration coefficients in the configuration (.con or .xmlcon) file.
  • Do a frequency check on the conductivity cell. Disconnect the plumbing on the cell. Rinse the cell with distilled or de-ionized water and blow it dry (use your mouth and not compressed air, as there tends to be oil in the air lines on ships). With the cell completely dry, check the frequency reading. It should read within a few tenths of a Hz of the 0 reading on your Calibration Sheet. If it does not, something is wrong with the cell and it needs to be repaired.

What are Configuration Sheets, and where can I find them for my instrument?

Configuration Sheets detail instrument communication settings, system configuration (auxiliary sensors, which channels are set up for which sensors), and sensor calibration coefficients. Configuration sheets are provided with the instrument, in both paper form (may be part of the manual) and on the CD-ROM.

Configuration Sheet locations vary, depending on the type of instrument and when it was shipped. If you cannot locate them, contact Sea-Bird and we will email copies.

What is Sea-Bird’s policy on upgrading instruments?

It is our policy to update firmware in instruments while they are here for calibration at no cost to the customer, but it is not our policy to routinely upgrade circuit cards. On some very old units that are being upgraded to support more external sensors, new pressure sensors, or other repairs, we sometimes discount the new circuit cards as part of the larger upgrade, as that makes the work easier for us to complete.

What do I need to send to Sea-Bird for calibration of my SBE 9plus, 25, or 25plus?

For calibration of the temperature and conductivity sensors, only the sensor modules need to be sent to Sea-Bird. It is not necessary to send the CTD main housing. See Shipping SBE 9plus, 25, and 25plus Temperature and Conductivity Sensors for details.

It is usually not necessary to recalibrate the pressure sensor as frequently as the temperature and conductivity sensors. Experience has shown that the sensor’s sensitivity function almost never changes; only the offset drifts. The offset drift can easily be measured by reading deck pressure against a barometer. This small drift is easily corrected (Seasave V7 and SBE Data Processing provide an entry for the offset drift in the instrument .con or .xmlcon file).

  • SBE 9plus and 25plus — If the pressure sensor does need to be calibrated, the entire CTD must be shipped to Sea-Bird.
  • SBE 25 — If the pressure sensor does need to be calibrated, only the modular SBE 29 pressure sensor needs to be sent to Sea-Bird. It is not necessary to send the CTD main housing.

Can I get my CTD calibrated in the low conductivity range for use in freshwater only?

No, Sea-Bird does not perform low or narrow range calibrations on our CTDs. However, CTDs are used successfully in many freshwater environments.

Conductivity calibrations performed at Sea-Bird are valid in the range of 0 – 9 S/m (or 0 – 7 S/m, as specified for some instruments), and the calibration coefficients can be applied in freshwater for accurate calculations of conductivity.

Sea-Bird recognizes that calibration using natural seawater and IAPSO standards for ocean conductivity ranges may result in a small offset and possible slope errors near zero conductivity. For example, the estimated magnitude of offset error is < 0.002 S/m, and of slope error is < 0.002 S/m per 1 S/m change. This is an example of a conservative error estimate for initial accuracy of conductivity sensors used in freshwater, which can be challenging to calculate due to lack of a freshwater standard. However, sensor precision will be near the resolution (0.00004 S/m). Sea-Bird CTDs provide high precision and sensor stability, allowing an accurate measure of conductivity gradients (dC/dz) or water sample differences, regardless of ‘true’ conductivity values.  For these reasons, Sea-Bird CTDs that have been calibrated in seawater can be used successfully in many freshwater systems.

Lastly, note that the Practical Salinity Scale (PSS-78) is defined as valid for salinity ranges from 2 – 42 PSU. For additional references on freshwater algorithms used in the limnology field, see the following literature:

  • Millero, Frank J. 2000. Equation of State for Freshwater. Aquatic Geochemistry, 6: 1 – 17.
  • Pawlowicz, R. 2008. Calculating the Conductivity of Natural Waters. L&O: Methods 6, 489 – 501.  

How do I find information about the options available with each instrument?

On the product page for each instrument, there are two tabs that provide ordering information:

  • Click the Configuration tab to see all the features and options available on our price list. The Configuration tab provides explanatory information, illustrations, and photographs describing each item.
  • Click the Accessories tab to see cables, mount kits, and/or spare parts for the products.

Third Party Sensor Configuration lists instruments and integration options for sensors produced by other manufacturers (altimeters, fluorometers, transmissometers, etc.).

Where do I find pricing information for new instruments, calibration services, and/or repair services?

Sea-Bird does not publish prices on the website. Please contact us for pricing:

Which Sea-Bird profiling CTD is best for my application?

Sea-Bird makes four main profiling CTD instruments, as well as several profiling CTD instruments for specialized applications.

In order of decreasing cost, the four main profiling CTD instruments are the SBE 911plus CTD, SBE 25plus Sealogger CTD, SBE 19plus SeaCAT Profiler CTD, and SBE 49 FastCAT CTD Sensor:

  • The SBE 911plus is the world’s most accurate CTD. Used by most leading oceanographic institutions, the SBE 911plus is recognized for superior performance, reliability, and ease-of-use. Features include: modular conductivity and temperature sensors, Digiquartz pressure sensor, TC-Ducted Flow and pump-controlled time response, 24 Hz sampling, 8 A/D channels and power for auxiliary sensors, modem channel for real-time water sampler control without data interruption, and optional 9600 baud serial data uplink. The SBE 911plus system consists of: SBE 9plus Underwater Unit and SBE 11plus Deck Unit. The SBE 9plus can be used in self-contained mode when integrated with the optional SBE 17plus V2 Searam. The Searam provides battery power, internal 24 Hz data logging, and an auto-fire interface to an SBE 32 Carousel Water Sampler to trigger bottle closures at pre-programmed depths.
  • The SBE 25plus Sealogger is the choice for research work from smaller vessel not equipped for real-time operation, or use by multi-discipline scientific groups requiring configuration flexibility and good accuracy and resolution on a smaller budget. The SBE 25plus is a battery-powered, internally-recording CTD featuring the same modular C & T sensors used on the SBE 9plus CTD, an integral strain gauge pressure sensor, 16 Hz sampling, 2 GB of memory, TC-Ducted Flow and pump-controlled time response, and 8 A/D channels plus 2 RS-232 channels and power for auxiliary sensors. Real-time data can be transmitted via RS-232 simultaneous with data recording. The SBE 25plus integrates easily with an SBE 32 Carousel Water Sampler or SBE 55 ECO Water Sampler for real-time or autonomous operation.
  • The SBE 19plus V2 SeaCAT Profiler is known throughout the world for good performance, reliability, and ease-of-use. An economical, battery-powered, internally-recording mini-CTD, the SBE 19plus V2 is a good choice for basic hydrography, fisheries research, environmental monitoring, and sound velocity profiling. Features include 4 Hz sampling, 6 differential A/D channels plus 1 RS-232 channel and power for auxiliary sensors, 64 MB of memory, and pump-controlled conductivity time response. Real-time data can be transmitted via RS-232 simultaneous with data recording, The SBE 19plus V2 integrates easily with an SBE 32 Carousel Water Sampler or SBE 55 ECO Water Sampler for real-time or autonomous operation.
  • The SBE 49 FastCAT is an integrated CTD sensor intended for towed vehicle, ROV, AUV, or other autonomous profiling applications. Real-time data ‑ in raw format or in engineering units ‑ is logged or telemetered by the vehicle to which it is mounted. The SBE 49’s pump-controlled, TC-ducted flow minimizes salinity spiking, and its 16 Hz sampling provides very high spatial resolution of oceanographic structures and gradients. The SBE 49 has no memory or internal batteries. The SBE 49 integrates easily with an SBE 32 Carousel Water Sampler or SBE 55 ECO Water Sampler for real-time operation.

The specialized profiling CTD instruments are the SBE 52-MP Moored Profiler, Glider Payload CTD, and SBE 41/41CP Argo CTD module:

  • The SBE 52-MP Moored Profiler is a conductivity, temperature, pressure sensor, designed for moored profiling applications in which the instrument makes vertical profile measurements from a device that travels vertically beneath a buoy, or from a buoyant sub-surface sensor package that is winched up and down from a bottom-mounted platform. The 52-MP's pump-controlled, TC-ducted flow minimizes salinity spiking. The 52-MP can optionally be configured with an SBE 43F dissolved oxygen sensor.
  • The Glider Payload CTD measures conductivity, temperature, and pressure, and optionally, dissolved oxygen (with the modular SBE 43F DO sensor). It is a modular, low-power profiling instrument for autonomous gliders with the high accuracy necessary for research, inter-comparison with moored observatory sensors, updating circulation models, and leveraging data collection opportunities from operational vehicle missions. The pressure-proof module allows glider users to exchange CTDs (and DO sensors) in the field without opening the glider pressure hull.
  • Argo floats are neutrally buoyant at depth, where they are carried by currents until periodically increasing their displacement and slowing rising to the surface. The SBE 41/41CP CTD Module obtains the latest CTD profile each time the Argo float surfaces. At the surface, the float transmits in-situ measurements and drift track data to the ARGOS satellite system. The SBE 41/41CP can be integrated with Sea-Bird's Navis float or floats from other manufacturers. The SBE 41N CTD is integrated with Sea-Bird's Navis Float with Integrated Biogeochemical Sensors and Navis BGCi + pH Float with Integrated Biogeochemical Sensors.

See Product Selection Guide for a table summarizing the features of our profiling CTDs.

I want to integrate a moored CTD with some auxiliary sensors (transmissometer, fluorometer, etc.). Which CTD should I use?

Sea-Bird currently manufactures only 1 moored CTD that can accept auxiliary sensors, the SBE 16plus V2 SeaCAT (and its inductive modem version, the 16plus-IM V2). These instruments measure conductivity and temperature; a pressure sensor is optional. They have 6 differential A/D channels and 1 RS-232 channel available for auxiliary sensors, which can be plugged into the CTD end cap.

The SBE 37 MicroCAT family includes CTDs that are integrated with a dissolved oxygen sensor at the factory.

Notes:

  • The SBE 19plus V2 SeaCAT, intended primarily for profiling applications, can also be used in moored mode. The 19plus V2 also has 6 differential A/D channels and 1 RS-232 channel available for auxiliary sensors. When in moored mode, it functions similar to a 16plus V2 with optional pressure sensor.
  • The older versions of these products, the SBE 16 / 16plus / 16plus-IM and SBE 19 / 19plus, also accept auxiliary sensors.

See Product Selection Guide for a table summarizing the features of all our moored instruments.

How should I pick the pressure sensor range for my CTD? Would the highest range give me the most flexibility in using the CTD?

While the highest range does give you the most flexibility in using the CTD, it is at the expense of accuracy and resolution. It is advantageous to use the lowest range pressure sensor compatible with your intended maximum operating depth, because accuracy and resolution are proportional to the pressure sensor's full scale range. For example, the SBE 9plus pressure sensor has initial accuracy of 0.015% of full scale, and resolution of 0.001% of full scale. Comparing a 2000 psia (1400 meter) and 6000 psia (4200 meter) pressure sensor:

  • 1400 meter pressure sensor ‑ initial accuracy is 0.21 meters and resolution is 0.014 meters
  • 4200 meter pressure sensor ‑ initial accuracy is 0.63 meters and resolution is 0.042 meters

I am ordering a CTD and want to use auxiliary sensors. Should I order them from Sea-Bird also, or deal directly with the sensors’ manufacturers?

This depends on your own expertise and resources. We have extensive experience in integrating and supporting a wide range of auxiliary sensors, but not everything under the sun. We have a large list of commonly used sensors that we routinely offer for sale (see Third Party Sensor Configuration).

When you purchase any of these auxiliary sensors from Sea-Bird, we are able to apply this experience to integrating the sensors with the CTD. The integration includes installing the sensors (with appropriate mounting kits and cables) in a manner that puts each sensor in the best possible orientation for optimum performance. It also includes configuring the CTD system and software to accept the sensors’ inputs and properly display the data, and testing the entire system, typically in a chilled saltwater bath overnight, to confirm proper operation. Having done the integration, we also support the entire system in terms of follow-on service and end-user support with operational and data analysis questions *. There is significant added value in our integration service, and there is some extra cost for this, compared to doing it yourself. However, we do not base our business on selling services, and the prices charged for Third Party sensors carry minimal mark-ups that vary depending on the pricing we are offered by the manufacturers. In some cases we can sell at the manufacturer's list price, and in others we have to add margin.

*Notes:
1. As described in our Warranty, auxiliary sensors manufactured by other companies are warranted only to the limit of the warranties provided by their original manufacturers (typically 1 year).
2. Click here for information on repairing / recalibrating auxiliary sensors manufactured by other companies.

What are the pros and cons of ordering wet-pluggable connectors? Can I mate and unmate a cable with this connector underwater?

Wet-pluggable (also referred to as wet-mateable or MCBH) connectors, an option on all of our underwater instruments, may be mated in wet conditions (click here for a photo comparison). Their pins do not need to be dried before mating. By design, water on the connector pins is forced out as the connector is mated. However, they must not be mated or un-mated while submerged. Wet-pluggable connectors have a non-conducting guide pin to assist pin alignment & require less force to mate, making them easier to mate reliably under dark or cold conditions, compared to our Impulse XSG/RMG connectors (XSG/RMG connectors may not seal well in extreme cold; we recommend connecting cables in warm ship’s lab rather than on deck for these conditions). Like XSG/RMG connectors, wet-pluggables need proper lubrication & require care during use to avoid trapping water in sockets.

Wet-pluggable connectors do add additional cost to the instrument. The increase in price is dependent on the number of pins on each connector, and the number of connectors on your instrument. When should you consider configuring your instrument with wet-pluggable connectors? Consider the following guidelines:

  • Internal recording with a profiling CTD (for example, SBE 9plus with 17plus V2, SBE 19plus V2, SBE 25plus) — Connecting/disconnecting frequently to the CTD is typical for these systems, for uploading of the internally recorded data. Wet-pluggable connectors are recommended for these applications.
  • Autonomous water sampling (SBE 32 Carousel with AFM or 17plus V2, or SBE 55 ECO Water Sampler) and internal recording with a profiling CTD — Connecting/disconnecting to the underwater electronics is required after every cast, to re-arm the electronics for autonomous water sampling. Connecting/disconnecting is often done on deck, where the connectors are exposed to splashing and rain; wet-pluggable connectors are strongly recommended for these applications.
  • Real-time data acquisition with a profiling CTD (for example, SBE 9plus with 11plus Deck Unit, SBE 19plus V2 with PDIM and SBE 33 or 36 Deck Unit, SBE 25plus with PDIM and SBE 33 or 36 Deck Unit) — The underwater units in these systems are plugged into the sea cable, and typically are disconnected infrequently. Wet-pluggable connectors are not as important for this application.
  • Moored instruments
    — If data upload after recovery will occur on deck to allow for quick redeployment, wet-pluggable connectors are recommended. 
    — If data upload after recovery will occur in a lab, wet-pluggable connectors are not as important for this application.

Note: Prior to 2005, the wet-pluggable connectors available had a rubber-to-metal seal that could break down with prolonged use (3 - 5 years); seal breakdown will lead to instrument flooding. Sea-Bird recommended frequent inspection of the connectors for damage. We also discouraged the use of wet-pluggable connectors for moored deployments, because they cannot be inspected during a prolonged deployment. 
From 2005 to 2007, Sea-Bird transitioned to the WB (water block) type of wet-pluggable connectors. WB connectors have a water block that minimizes the possibility of instrument flooding; we do not discourage the use of these types of connectors for moored deployments. If you have wet-pluggable connectors on your instrument and are unsure of which type you have, contact Sea-Bird.

Can Sea-Bird provide some guidance for ordering cable, winch, and deck gear?

For a Sea-Bird CTD used with one of our Deck Units (SBE 11plus, SBE 33, or SBE 36), the electrical requirements of the armored cable are simple. Only one conductor is required (the armor is used as ground) and the total 2-way resistance (conductor plus armor) should be under 350 ohms. The mechanical requirements are most driven by the characteristics of the winch and weight of the payload to be lifted. The winch should have a level wind device which is either adjustable or pre-designed to lay the correct number of wraps across the drum, as determined by the cable diameter and drum width. The winch must also be equipped with a slip ring (rotating contact) assembly (at least 2 channels). A cable breaking strength of at least 5 to 7 times the maximum payload weight is recommended for safety and cable longevity. The cable must also be terminated both mechanically and electrically at the underwater (instrument) end. Cable termination (mechanical) at the winch drum is usually addressed by the winch maker. The cable is terminated electrically to the slip ring per the slip ring manufacturer's specification.

Sea-Bird is not expert in winch and deck gear and cannot recommend a block and A-frame. From past experience and with knowledge of what other customers use, we can point out sources for typical cable solutions, and cable terminations suppliers. For links to suppliers of winches, cable, and cable termination hardware, see Third Party Equipment.

Should I purchase spare sensors for my SBE 9plus or 25plus?

Most customers purchase spare conductivity and temperature sensors. These sensors are exposed to ocean conditions and therefore more likely to be broken than an internal sensor. It is also very easy to change them because they are independent sensors that plug into the CTD main housing.

Most customers do not purchase spare pressure sensors for the following reasons:

  • The pressure sensor is inside the CTD main housing. It is very well protected against damage of any kind, and reliability of this sensor is extremely good.
  • The sensor is expensive.
  • It is difficult to change the sensor in the field.

How many/what kind of spares should I have on ship for my SBE 9plus?

The most complete backup system would be another SBE 9plus, to allow for very rapid system swaps. This is important if your stations are close together and there is limited time between CTD casts. However, it is the most expensive option.

The next step down would be an SBE 9plus without sensors. In this case, a system failure would require swapping sensors and pumps to the new unit. This is not difficult, but it is somewhat time consuming. If you have several hours between casts it should not be a problem.

The next option would be to carry spare boards and try and troubleshoot the problem and replace boards. If you have a technician that can do this it is not a bad option. However, it requires some clean and dry lab space to open the CTD and work. You will also have to properly re-seal the CTD. Based upon experience, the SBE 9plus does not fail very often. The most common failure is the main DC-to-DC converter. Other than that, there are very few system failures. However, there are several components that can be damaged through mistakes or misuse. The most catastrophic, other that losing the whole CTD, is to plug the sea cable into the bottom contact connector on the bottom end cap; if this happens, several circuit boards will be destroyed (Note: In 2007 Sea-Bird began using a female bulkhead connector on the 9plus for the bottom contact switch, to differentiate from the sea cable connector and prevent this error. If desired, older CTDs can be retrofitted with the female connector.).

If the budget allows it, we recommend getting a complete backup SBE 9plus, including sensors. If there is any problem, return the malfunctioning instrument for repair and continue sampling with the spare instrument. A complete backup also provides you with spare sensors, so you can rotate 1 set through calibration and continue to operate.

How many/what kind of spares should I have on ship for my instrument?

Very few Sea-Bird instruments completely fail due to component malfunction or manufacturing defects. However, we see a reasonably large number that require repairs of some sort. Most of these are simply due to the user breaking the equipment through rough handling, accidents, or lack of maintenance. It always best to plan for the worst case.

Parts most likely to be damaged are cables, connectors, and sensors (specifically the conductivity cell). Cables and connectors are easily replaced and spares should always be carried. After a sensor is replaced, the instrument must be re-calibrated, so it is really not practical to carry spare cells or temperature probes. If you start carrying many spare boards and sensors you are better off (both in cost and efficiency) having whole spare instruments on board.

Carrying at least 1 complete set of spares, with 3 sets of cables, connectors and dummy plugs, is recommended. How fast you can get spares from shore to the ship should dictate how many spare systems you need to have on board.

Note: See spares recommendations specific to the SBE 9plus.

Where can I purchase standard seawater?

IAPSO standard seawater is available in 250 ml vials. For more information and purchase inquiry, e-mail osil@oceanscientific.co.uk.

What is Triton? Do I need to purchase it from Sea-Bird?

Triton X-100 is Octyl Phenol Ethoxylate, a reagent grade non-ionic surfactant (detergent). Sea-Bird uses it to help keep our conductivity cells clean and the electrodes wetted and ready for immediate use in water (a dry cell requires a few minutes to become completely wetted after immersion). Triton X-100 will not harm conductivity cells, temperature sensors, or pumped fluorometers. Do not place concentrated Triton X-100 directly on the membrane or optical window of a dissolved oxygen sensor.

Triton X-100 is supplied in 100% strength.

Triton X-100 can be ordered from Sea-Bird, but should also be available locally from a chemical supply or laboratory products companies. It is manufactured by Avantor Performance Materials (see http://www.avantormaterials.com/commerce/product.aspx?id=2147509608). See our MSDS page to view the Material Safety Data Sheet.

Do you recommend a particular brand of alkaline D-cell batteries?

For Sea-Bird instruments that use alkaline D-cells, Sea-Bird uses Duracell MN 1300, LR20. While rare, we have seen a few problems with cheaper batteries over the years: they are more likely to leak, may vary in size (leading to loose batteries causing a bad power connection), and may not last as long.

Does Sea-Bird pressure test each instrument before shipping to verify integrity of housing, o-rings, assembly, etc.?

We pressure test each Sea-Bird instrument to the smaller of:

  • The housing depth rating, or
  • (if pressure sensor installed) The maximum rating of the pressure sensor

Note: Sea-Bird does not pressure test auxiliary sensors supplied by Third Party Manufacturers that are to be integrated with Sea-Bird instruments.

Does Sea-Bird check and calibrate all sensors on a CTD system prior to shipping?

Your entire system is assembled and tested prior to leaving our facility, with software configured to your specific setup. All Sea-Bird manufactured instruments/sensors are calibrated in-house. Sensors from third party manufacturers are calibrated by their manufacturers prior to integration with the CTD system.

Do Sea-Bird instruments have CE certification?

There are a number of classes of products that are excluded from the EU requirement for CE certification; underwater sensors and equipment are among the types of products that do not require CE certification. However, Sea-Bird decided to obtain CE certification to ease concerns of customers in the EU.

In 2009 Sea-Bird obtained CE certification for almost all of our instruments; we have CE labels on these instruments and provide the required documentation. There is a CE label on the manual front cover for each certified instrument; see our Model List page to download the manual for a specific instrument to check for the CE label.

Do Sea-Bird instruments have ISO certification?

Sea-Bird instruments do not have ISO certification. ISO certification does not certify that a manufacturer is producing a high quality product; it merely certifies that a company has a quality control plan that complies with the quality control models adopted by the ISO organization. This does not mean that other quality control systems are inferior. Sea-Bird has intentionally not become ISO-certified, because the ISO quality control model interferes with our own and would make it much harder, slower, and more expensive to remain at the leading edge of oceanographic instrument technology and serve the best interests of ocean scientists.

Does it matter whether you use natural or artificial seawater for calibrations? Which does Sea-Bird use?

For SBE 4 conductivity calibrations, Sea-Bird uses natural seawater that has been carefully collected, stored, UV irradiated, and filtered. Artificial seawater is not adequate if calibration errors are to be kept below 0.010 psu.
Note: SBE 4 is the conductivity sensor in the SBE 9plus, 25, and 25plus profiling CTDs.

The primary difference between natural and artificial seawater is the behavior of conductivity versus temperature. The practical salinity scale 1978 equations include a term rt. This term is expanded into a fourth order equation that describes the variation of conductivity versus temperature for a sample of constant salinity. The equation’s coefficients are derived by fitting to natural seawater samples. Artificial seawater does not have the same conductivity versus temperature characteristic, providing incorrect coefficients and causing a slope error in the calibration.

For calibrations of conductivity sensors other than the SBE 4, Sea-Bird uses artificial seawater (NaCl solution). However, we place an SBE 4 conductivity sensor in each bath, providing a standard for reference to the natural seawater calibration. This allows us to correct errors in the coefficients and slope introduced with the artificial seawater calibration.

For calibration of temperature sensors, Sea-Bird uses artificial seawater (NaCl solution).

Can I use a pressure sensor above its rated pressure?

Digiquartz pressure sensors are used in the SBE 9plus, 53, and 54. The SBE 16plus V2, 16plus-IM V2, 19plus V2, and 26plus can be equipped with either a Druck pressure sensor or a Digiquartz pressure sensor. All other instruments that include pressure use a Druck pressure sensor.

  • The overpressure rating for a Digiquartz (as stated by Paroscientific) is 1.2 * full scale. The sensor will provide data values above 100% of rated full scale; however, Sea-Bird does not calibrate beyond the rated full scale.
  • The overpressure rating for a Druck (as stated by Druck) is 1.5 * full scale. The sensor will provide data values above 100% of rated full scale; however, Sea-Bird does not calibrate beyond the rated full scale.

Note: If you use the instrument above the rated range, you do so at your own risk; the product will not be covered under warranty.

What is the function of the zinc anode on some instruments?

A zinc anode attracts corrosion and prevents aluminum from corroding until all the zinc is eaten up. Sea-Bird uses zinc anodes on an instrument if it has an aluminum housing and/or end cap. Instruments with titanium or plastic housings and end caps (for example, SBE 37 MicroCAT) do not require an anode.

Check the anode(s) periodically to verify that it is securely fastened and has not been eaten away.

Why is Teflon tape used?

Adhesive Teflon tape (actually, UHMW tape — Ultra High Molecular Weight polyethylene) provides insulation to prevent damage due to contact of dissimilar metals. It is typically used by Sea-Bird on the inside of hose clamps used for mounting instruments, where U-bolts hold a Carousel Water Sampler frame to an extension stand, etc. The tape can be ordered from Sea-Bird; part number 30409 is 1 inch wide x 0.1 inch thick x 1 foot long (2.5 cm x 0.25 cm x 0.3 m). It can also be purchased from the manufacturer, Crown Plastics (see www.crownplastics.com for local distributors).

What are the differences between salinity expressions in ppt, psu (Practical Salinity), and Absolute Salinity?

The numeric difference between psu and ppt is small; both indicate ocean salinity. Prior to 1978, oceanographers referred to the physical quantity  ppt (kg salt per kg water in parts per thousand). In 1978, the Practical Salinity Scale (PSS-78) was adopted, which yields a practical salinity from equations, smooth expansions of conductivity ratio, which were carefully fit to the real salinity of diluted North Atlantic seawater. The numeric unit from PSS-78 is psu (practical salinity unit). The primary motivation for psu was consistency; it focused on a trace to a primary conductivity standard (K15) and recognition that ocean ion ratios were not identical. Salinometer work was plagued by an inconsistent standard and the ppt equations included ion ratios from different oceans. So, the trade was a consistent standard and equation that works for a single ion mix instead of exact salinity in other ocean basins. G. Siedler and H. Peters highlighted where PSS-78 and EOS-80 formulas deviate from real salinity and density (e.g., Baltic Sea is difficult, but the deep Pacific has EOS-80 deviations of up to 0.02 kg/m3, implying salinity errors of order 0.02 psu).

In June 2009, a new Thermodynamic Equation of State of Seawater, referred to as TEOS-10, was adopted by the Scientific Committee on Oceanic Research and the International Association of Physical Sciences of the Ocean Working Group 127. The new equation incorporates a more accurate representation of salinity known as Absolute Salinity. Application Note 90 discusses this new equation, and Sea-Bird's implementation in SBE Data Processing.

Is the salinity calculated by Sea-Bird valid above 42 psu?

The modern oceanographic definition of salinity is the Practical Salinity Scale of 1978 (PSS-78). By definition, PSS-78 is valid only in the range of 2 to 42 psu. Sea-Bird uses the PSS-78 algorithm in our software, without regard to those limitations on the valid range.

Unesco technical papers in marine science 62 "Salinity and density of seawater: Tables for high salinities (42 to 50)" provides a method for calculating salinity in the higher range (access this paper via Unesco's website).

What is the difference in temperature expressions between IPTS-68 and ITS-90?

ITS-90 was adopted in 1990 as the temperature scale; IPTS-68 was the previous standard. The differences are related to redefining certain triple points and other melt or freeze cells that are used as the fundamental standards for temperature. Over the oceanographic ranges of temperature, a linear approximation is used to convert:

IPTS-68 = 1.00024 * ITS-90

The difference is small, but at WOCE levels it is significant.

Note: Salinity, density, and sound velocity are still defined in terms of IPTS-68 temperature. Sea-Bird’s software uses IPTS-68 temperature to calculate these derived parameters, regardless of which temperature scale you select for outputting or plotting temperature.

Application Note 42: ITS-90 Temperature Scale provides a more detailed description.

What is the difference between initial accuracy and resolution?

Upon receipt of an instrument, the initial accuracy is the accuracy when comparing to a known standard. Resolution is the smallest amount of change that a sensor can see.

Why is sound velocity (SV) computed from a CTD better than sound velocity from direct measuring instruments?

Direct SV probes measure the time (flight time) required for a sound pulse to travel over a fixed length, using a high-speed clock to measure time. The clock starts when the pulse is emitted, and stops when the pulse is received. Theoretically, you only need to know the path length (and frequency of the clock ‑ an easy matter) to compute SV:

SV = acoustic path length / flight time.

For a typical acoustic path of 0.1 m, a flight time of 67 microseconds is expected for SV = 1492 m/s.

Two problems associated with direct SV probes are:

  • The path length is not readily determined by a ruler measurement. The true length includes some depth into the acoustic transducer at which the pulse actually arises and again some depth where it is actually detected. Consider for example an typical instrument with specified accuracy of 0.05 m/s. For a typical water SV of 1500 m/s and a probe acoustic path of 100 mm, achieving this accuracy requires that length be determined to within (0.05/1500) x 100 mm = 0.003 mm (approximately 1/25 the thickness of a sheet of paper). The acoustic transducer would be of order 1 mm thick, so its dimension is much larger (300 times) than the length associated with the specified accuracy.
  • Determining the actual flight time is not as simple as counting clock pulses. There are other time delays in determining both the start of the acoustic pulse and the time of its reception. Recalling that the time sound requires to travel 100 mm is approximately 67 microseconds, to measure SV to within 0.05 m, the flight time must be determined to within (0.05/1492) x 67 microseconds = 2.2 nanoseconds. It is exceedingly difficult to measure time to such precision, especially as the time lag associated with the acoustic transducer is much larger than this ‑ typically of order 1 microsecond (hundreds of times larger than the permitted error).

The fact is that in designing a direct path SV probe, the determination of length by ruler is only good to 5 or 10% (approximately 100 m/s equivalent uncertainty in SV). The actual determination of SV response therefore must be made in a calibration bath (using a CTD as a reference!), which is how all SV probes are calibrated.

Direct SV probes are often marketed on the principle that the measurement is based only on fundamental physical values of length and time. That is true in theory, but the practice is a different story! Direct SV probe manufacturers do not know the length (or the time) — they just fit the probe response to CTD-computed SV. There is a place for direct SV probes. Having been calibrated in water against a CTD, they do a competent job of measuring SV in other liquids. They will go on working in oil, petrol, milk, beer, etc. — liquids in which CTD measurements have no meaning.

Which algorithm for calculating sound velocity (SV) from CTD data should I use?

Sea-Bird real-time data acquisition (Seasave V7) and data processing (SBE Data Processing) software supports calculation of Chen-Millero, Del Grosso, and Wilson sound velocities. The algorithms, as implemented in our software, are provided in the software documentation, which is available via the software Help files or in an Appendix in the software manuals.

The Hydrographic Society published Special Publication No. 34 in 1993, "A Comparison Between Algorithms for the Speed of Sound in Seawater", comparing a number of sound velocity algorithms. The report recommends using the Chen-Millero algorithm for water depths less than 1000 meters and the Del Grosso algorithm for water depths greater than 1000 meters, and recommends that the Wilson algorithm should not be used. Access the report via the Hydrographic Society's website.

How can I find the density of seawater at different temperatures and/or salinities?

SBE Data Processing includes a module called Seacalc III. Seacalc III can calculate density, sound velocity, and a number of other parameters for a given user input of pressure, temperature, and conductivity (or salinity).

What is the cause of conductivity drift?

Conductivity cells drift primarily as a function of cell fouling. There are several sources of the fouling:

  • Biological growth is the primary source of cell fouling. Rinsing the conductivity cell with clean de-ionized water after each cast helps prevent most growth in the cell. If the cell is not rinsed, or standard tap water is used, growth rates can be severe. As the cell fouls, it will drift towards lower salinity values.
  • Surface oil slicks also cause cell fouling. Avoid deploying the CTD through obvious slicks. When working in coastal areas, with higher chances of oil fouling, rinse and soak the cell with a 1% Triton X-100 solution (diluted in clean DI water) to help prevent oil fouling.

See Application Note 2D: Instructions for Care and Cleaning of Conductivity Cells for rinsing, cleaning, and storage procedures.

Because of the nature of fouling, the total cell drift may not be linear. It exhibits rapid small shifts (especially if related to oil fouling) on top of a base line drift. It is important to take water samples to document the behavior. Application Note 31: Computing Temperature and Conductivity Slope and Offset Correction Coefficients from Laboratory Calibrations and Salinity Bottle Samples discusses how to correct the data.

Does it matter whether you use natural or artificial seawater for calibrations? Which does Sea-Bird use?

For SBE 4 conductivity calibrations, Sea-Bird uses natural seawater that has been carefully collected, stored, UV irradiated, and filtered. Artificial seawater is not adequate if calibration errors are to be kept below 0.010 psu.
Note: SBE 4 is the conductivity sensor in the SBE 9plus, 25, and 25plus profiling CTDs.

The primary difference between natural and artificial seawater is the behavior of conductivity versus temperature. The practical salinity scale 1978 equations include a term rt. This term is expanded into a fourth order equation that describes the variation of conductivity versus temperature for a sample of constant salinity. The equation’s coefficients are derived by fitting to natural seawater samples. Artificial seawater does not have the same conductivity versus temperature characteristic, providing incorrect coefficients and causing a slope error in the calibration.

For calibrations of conductivity sensors other than the SBE 4, Sea-Bird uses artificial seawater (NaCl solution). However, we place an SBE 4 conductivity sensor in each bath, providing a standard for reference to the natural seawater calibration. This allows us to correct errors in the coefficients and slope introduced with the artificial seawater calibration.

For calibration of temperature sensors, Sea-Bird uses artificial seawater (NaCl solution).

Where can I purchase standard seawater?

IAPSO standard seawater is available in 250 ml vials. For more information and purchase inquiry, e-mail osil@oceanscientific.co.uk.

Why is my CTD data showing hysteresis?

The difference between downcast and upcast is most likely related to package wake. When the CTD is mounted under a large water sampler, the variation can be on the order of 5 to 8 meters. This is due to the shadowing of the CTD sensors by the water sampler.

When I compute sigma-density values, why are they sometimes negative?

For convenience while examining differences in density between two water parcels, Sigma-density values are typically used by oceanographers. Sigma-density values allow the oceanographer to focus on the last 6 to 7 digits in the density value (when assuming 5 decimal place resolution), as this is where most of the variation in density occurs. Sigma-density values are also a shorthand way for representing density of a water parcel with some specific modification to one of the density computational inputs, like pressure or temperature.

Examples:

  • Sigma = (rho(t,s,p) - 1000) kg/m3
  • Sigma-t = (rho(s,t,p=0) - 1000) kg/m3 (density at atmospheric pressure)
  • Sigma-theta = (rho(t=theta,s,0) - 1000 kg/m3 (density with effect of adiabatic cooling/heating effect [using potential temperature] and the pressure effect removed).


So, though the true density of water is always a value that is non-negative, when testing instruments on the bench (zero salinity) or in freshwater systems, the computed density can be < 1000 kg/m3. In this situation, when converting density to a Sigma-density value, it is possible for the Sigma-density value to be negative.

Example: S = 0, t = 5 deg C, and pressure = 0
rho(S,t,pressure) = 999.96675 kg/m3
Sigma-t (t,S,0) = - 0.03325

For more information on the Practical Salinity Scale (1978) and the Equation of State for Seawater (EOS-80), refer to UNESCO Technical Papers of Marine Science 44.

Note: Many UNESCO marine science publications are available through UNESCO's website. Go to http://unesdoc.unesco.org/ulis/ioc/.

  1. In the Series title box, select UNESCO technical papers in marine science.
  2. Select Widen the search to all UNESCO documents/publications.
  3. Click the OK button.

How accurate is salinity measured by my CTD? What factors impact accuracy?

One of the reasons that this is not a simple question is that there are several factors to take into consideration regarding the error margin for practical salinity measurements. Salinity itself is a derived measurement from temperature, conductivity, and pressure, so any errors in these sensors can propagate to salinity. For example, Oour initial accuracy specification for the SBE 3plus temperature sensor and SBE 4 conductivity sensor on an SBE 9plus CTD is approximately equivalent to an initial salinity accuracy of 0.003 PSU (note that conductivity units of mS/cm are roughly equivalent in terms of magnitude to PSU).

However, another issue to consider is that this accuracy is defined for a clean, well-mixed calibration bath. In the ocean, some of the biggest factors that impact salinity accuracy are 1) sensor drift from biofouling or surface oils for conductivity in particular and 2) dynamic errors that can occur on moving platforms, particularly when conditions are rapidly changing, which will be true for all sensors that measure salinity. Sea-Bird provides recommendations, design features such as a pumped flow path, and data processing routines to align and improve data for the salinity calculation to account for thermal transients and hysteresis, and to match sensor response times.  Depending on the environment and the steepness of the gradient, and after careful data processing, this may continue to have an impact on salinity on the order of 0.002 PSU or more, for example. For more details, see Application Note 82.

Lastly, note that salinity in PSU is calculated according to the Practical Salinity Scale (PSS-78), which is defined as valid for salinity ranges from 2 – 42 PSU.