SBE 21 SeaCAT Thermosalinograph

Externally powered thermosalinograph for shipboard determination of sea surface (pumped-water) conductivity and temperature. Internal memory, acquisition of NMEA navigational data and remote temperature data, and capability to interface with auxiliary sensors.

The externally powered SBE 21 accurately determines sea surface temperature and conductivity from underway vessels. Data is simultaneously stored in memory and output to a computer in real-time. Typically mounted near the ship’s seawater intake, the SBE 21 connects to an AC-powered interface box near a computer. The interface box provides power and an isolated data interface, and contains a NMEA 0183 port for appending navigation data.

Memory capacity exceeds 10.6 million samples of temperature and conductivity; real-time output continues after the memory is full.

Bulkhead connectors are provided for optional auxiliary sensors:

  • RS-232 interface for an SBE 38 temperature sensor. The SBE 38, installed at the seawater intake (ideally near the bow), measures sea surface temperature with minimal thermal contamination from the hull.
  • Four single-ended or two differential 0-5 volt A/D input channels for voltage output auxiliary sensors.

FEATURES

  • Conductivity, Temperature, and auxiliary sensor data (SBE 38 remote temperature sensor and up to 4 voltage output sensors), continuously at 4 Hz (averaging, storing, and transmitting data at user-programmable 3-to 600-sec intervals) or taking a single measurement at user-programmable 3- to 600-sec intervals.
  • Internal memory, powered externally.
  • Expendable anti-foulant devices for bio-fouling protection.
  • Valve control of seawater circulation and fresh-water flushing; sensor assembly easily removed for cleaning and calibration.
  • Seasoft© V2 Windows software package (setup, and data acquisition, upload, and processing).
  • SeaCAT family, field-proven since 1987.
  • Five-year limited warranty.

COMPONENTS

  • Unique internal-field conductivity cell eliminates proximity effects. This is critically important for thermosalinographs, where the cell operates in a water jacket’s confined volume, and also permits use of expendable anti-foulant devices, for long-term bio-fouling protection.
  • Aged and pressure-protected thermistor has a long history of exceptional accuracy and stability.

MECHANICAL INSTALLATION

The PVC base or back plate may be drilled for mounting to the ship. Seawater connections (for normal use) and fresh water connections (for cleaning) are PVC pipes with 1-inch (25.4-mm) U.S. standard NPT threads. Mating female fittings are provided, and can easily be adapted to locally available pipe sizes. A stainless steel and plastic in-line pipe mount is available for safe below-waterline installation of the remote temperature sensor.

SCHEMATIC

Notes:
1. Seasave also supports acquisition of data from a NMEA device connected directly to computer (instead of Interface Box).
2. Some installations require a de-bubbler. Click here for information on a de-bubbler produced by the State University of New York, Ocean Instrument Laboratory; information provided for reference only.

Measurement Range

Conductivity 0 to 7 S/m
Temperature -5 to +35 °C
Temperature, SBE 38 remote -5 to +35 °C

Initial Accuracy

Conductivity ± 0.001 S/m
Temperature ± 0.01 °C
Temperature, SBE 38 remote ± 0.001 °C

Resolution

Conductivity 0.0001 S/m typical
Temperature 0.001 °C
Temperature, SBE 38 remote 0.0003 °C

Miscellaneous

Sample Interval 4 Hz (averaging, storing, and transmitting at user-programmable 3-to 600-sec intervals);
or single measurement at user-programmable 3-to 600-sec intervals
Memory T & C: 10.6 million samples;
T, C, SBE 38, & 4 voltage sensors: 3.7 million samples
Water Jacket Volume approximately 5 liters
Recommended Flow Rate approximately 1 liter/sec
Operating Pressure 34.5 decibars (50 psi) maximum
Dimensions & Weight 57.7 high x 48.3 wide x 22.9 cm; 41 kg
The list below includes (as applicable) the current product brochure, manual, and quick guide; software manual(s); and application notes.

For older SBE 21 product manuals, organized by instrument firmware version, click here.

Title Type Publication Date PDF File
SBE 21 Brochure Product Brochure Tuesday, June 23, 2015 21brochureJun15.pdf
SBE 21 Manual Product Manual Monday, February 9, 2015 21_028.pdf
SeaCAT/Sealogger Interface Box Product Manual Wednesday, June 15, 2016 NMEAInterfaceBox_018.pdf
Seasave V7 Manual Software Manual Thursday, May 26, 2016 Seasave_7.26.0.pdf
SBE Data Processing Manual Software Manual Thursday, May 26, 2016 SBEDataProcessing_7.26.0.pdf
Field Service Bulletin 13: Jackscrew Replacements Field Service Bulletins Monday, March 8, 2010 FSB13.pdf
Field Service Bulletin 9: SeaCAT FlashInit Error Field Service Bulletins Monday, March 8, 2010 FSB9.pdf
Seasave V7 Quick Guide Software Quick Guide Tuesday, August 3, 2010 Seasave_ReferenceSheet_001.pdf
AN02D: Instructions for Care and Cleaning of Conductivity Cells Application Notes Monday, June 13, 2016 appnote2DJun16.pdf
AN06: Determination of Sound Velocity from CTD Data Application Notes Tuesday, February 2, 2010 appnote06Aug04.pdf
AN08: Sea-Bird Universal Opto-isolated Junction Box Application Notes Friday, March 7, 2008 appnote08.pdf
AN10: Compressibility Compensation of Sea-Bird Conductivity Sensors Application Notes Tuesday, May 7, 2013 appnote10May13.pdf
AN12-1: Pressure Port Oil Refill Procedure and Nylon Capillary Fitting Replacement Application Notes Friday, September 12, 2008 appnote12-1Sep08.pdf
AN14: 1978 Practical Salinity Scale Application Notes Thursday, January 12, 1989 appnote14.pdf
AN31: Computing Temperature and Conductivity Slope and Offset Correction Coefficients from Laboratory Calibrations and Salinity Bottle Samples Application Notes Monday, June 13, 2016 appnote31Jun16.pdf
AN33: Using the DC Opto Isolated Junction Box [PN 91118] Application Notes Saturday, March 3, 2001 appnote33.pdf
AN42: ITS-90 Temperature Scale Application Notes Wednesday, May 18, 2016 appnote42May16.pdf
AN57: Connector Care and Cable Installation Application Notes Tuesday, May 13, 2014 appnote57Jan14.pdf
AN67: Editing Sea-Bird .hex Data Files Application Notes Monday, October 15, 2001 appnote67.pdf
AN68: Using USB Ports to Communicate with Sea-Bird Instruments Application Notes Friday, October 19, 2012 appnote68Oct12.pdf
AN70: Installing Anti-Foulant Device Mount Kit on SBE 4, 16, 19, and 21 Conductivity Cells Application Notes Monday, May 19, 2008 appnote70May08.pdf
AN90: Absolute Salinity and TEOS-10: Sea-Bird's Implementation Application Notes Tuesday, September 3, 2013 AppNote90Sep13.pdf
Seaterm© is a terminal program for setup and data upload of a wide variety of older Sea-Bird instruments. Seaterm is part of our Seasoft V2 software suite.
Version 1.59 released October 10, 2007
Seaterm_Win32_V1_59.exe for Windows XP/Vista/7


Seasave V7© acquires, converts, and displays real-time or archived raw data from Sea-Bird profiling CTDs and thermosalinographs, as well as the SBE 16 family of moored CTDs. Seasave V7 is part of our Seasoft V2 software suite.
Version 7.26.2 released September 6, 2016
SeasaveV7.26.2-b13.exe for Windows XP/Vista/7


SBE Data Processing© consists of modular, menu-driven routines for converting, editing, processing, and plotting of oceanographic data acquired with Sea-Bird profiling CTDs, thermosalinographs, and the SBE 16 and 37 families of moored CTDs. SBE Data Processing is part of our Seasoft V2 software suite.
Version 7.26.2 released September 6, 2016


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 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.

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 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.

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 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 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.

 

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.

Family Model . Electronics Housing Auxiliary A/D Channels Water jacket
21   . 1 – Connector for SBE 38 interface 1 – 4 single-ended 1 – yes
        2 – 2 differential  

Example: 21.121x is an SBE 21 with connector for SBE 38 remote temperature sensor (order SBE 38 separately), 2 differential A/D channels, and water jacket. See table below for description of each selection:

PART # DESCRIPTION NOTES
21

SeaCAT THERMOSALINOGRAPH - With PVC (plastic) manifold & water jacket for shipboard installation. Includes 64 MB memory, 3 bulkhead connectors for data I/O, A/D inputs, remote sea surface thermometer (SBE 38 not included), AF24173 Anti-Foulant Devices, AC interface junction box (PN 90488.2) providing optically isolated RS-232 interface, NMEA 0183 input port for navigation data, DC power to sensors (10 m data I/O cable 80438, 3 m computer cable, NMEA test cable 801424, & AC power cord included), Seasoft software, & complete documentation.


Note: Seasave also supports acquisition of data from a NMEA device connected directly to computer (instead of deck unit).

Notes:

  • See SBE 45 for thermosalinograph without memory or A/D auxiliary sensor channels.
  • Some installations require a de-bubbler. See PN 70271 under Spares & Accessories.
SBE 21 Auxiliary A/D Channel Configuration Selections — MUST SELECT ONE
21.111 4 single-ended A/D channels Auxiliary 0 - 5 V sensors plug into 1 bulkhead connector on SBE 21 top cap.
  • 21.111 provides 1 bulkhead connector for 4 single-ended A/D channels. Single-ended channels are acceptable for sensors that draw very little current & can share power & signal common with SBE 21 without injecting ground line noise into signal.
  • 21.121 provides 1 bulkhead connector for 2 differential A/D channels (can also be used with 2 single-ended A/D sensors). Sensors that draw larger amounts of current generate ground line noise which interferes with signals. For these sensors, when power & signal common are shared, a differential channel is needed. Differential input amplifiers are able to distinguish & reject noise from signal.

Note: 21.111 & 21.121 do not include auxiliary sensors, mounts, or interface cables.

Many auxiliary sensors are electrically compatible with SBE 21; these sensors can be purchased from Sea-Bird & integrated with SBE 21 at our factory, or you can purchase cables from Sea-Bird & perform integration yourself. Note that integration of these sensors at Sea-Bird is limited to providing appropriate cable & setting up instrument configuration file. Sea-Bird does not provide methods for mechanical integration of these auxiliary sensors with SBE 21. User must design / provide flow-through chamber that receives outflow from SBE 21 for auxiliary sensors.

  • See Third Party portion of price list for ordering details on fluorometers, transmissometers, turbidity meters, etc. that are electrically compatible with SBE 21. These sensors can be purchased from Sea-Bird, along with appropriate cables. Alternatively, you can purchase sensors from third party manufacturers, & purchase cables from Sea-Bird.

User can change sensors on SBE 21 in field, if combination is compatible with auxiliary A/D channel configuration selection. However, bulkhead connector requires Y-cable to connect multiple auxiliary sensors to SBE 21; each Y-cable is unique to sensors being integrated, so changing sensors may require changing Y-cable.

21.121 2 differential A/D channels
SBE 21 Remote Sea Surface Thermometer Option
38.110x SBE 38 Digital Oceanographic Remote Seawater Intake Thermometer (titanium housing, XSG connector) Standard SBE 21 with serial number greater than 3110 supports input from remote SBE 38 thermometer through 4-pin remote temperature connector, providing sea surface temperature. Ideal location for SBE 38 is on pipe near seawater intake, as close to ship's bow as possible, to minimize water temperature changes due to ship's thermal mass. User can add SBE 38 to system at any time.
  • Some custom SBE 21s with serial number less than 3345 & greater than 3110, & all standard SBE 21s with serial number less than 3110, supported input from remote SBE 3 temperature sensor through a 3-pin remote temperature connector. Current SBE 21 electronics does not support SBE 3 as remote temperature sensor.
Shown below is SBE 38 installed in 50244 mounting kit; see document 67071.
50244 Stainless steel/plastic pipe coupling mounting kit for SBE 38 remote sensor (1 inch female NPT thread) with dummy sensor plug
171012 SBE 38 interface cable, 10 m (DN 31311)
SBE 21 Spares & Accessories
90488.2
Buy Now
RS-232 & Navigation Interface Box for SeaCATs / Sealoggers (SBE 16, 16plus, 16plus V2, 19, 19plus, 19plus V2, 21, or 25), AC powered. Provides isolated power, opto-isolated RS-232C & NMEA 0183 compliant interfaces, & up to 2 amps at 12 VDC to power a NMEA navigation device. NMEA interface merges position data with CTD data. Includes AC power cord & necessary interface cables & mating connectors, manual & software CD. One Interface Box comes standard with SBE 21; this is spare. Box comes with:
  • PN 17015 — AC power cable
  • PN 80438 (DN 31063) — 10 m cable for connection to SBE 21
  • PN 17031 (DN 30581) — 2.4 m pigtail cable for connection to SBE 21
  • PN 801424 (DN 32787) — 1.8 m NMEA test cable for connection to computer simulating NMEA input for testing NMEA interface. NMEA simulation program, NMEATest, is part of Seasoft software, & is installed when you install SBE Data Processing.
  • PN 171887 (DN 32431) — 3 m cable for connection to computer
  • PN 171888 — Cable adapter, DB-25S to DB-9P (for use with computer with DB-25 connector)
  • PN 50368 — connector assembly for 4-pin SeaCAT Data I/O (for connection to SBE 21)
  • PN 50369 — connector assembly for 5-pin NMEA Input (for connection to NMEA device; can acquire latitude/longitude & depth data)
50298
Buy Now
Thermosalinograph spares kit (SBE 38 interface) - contains connectors, o-rings, titanium hardware, & maintenance items Spares kit for use with SBE 21 that has 4-pin bulkhead connector for remote temperature input — compatible with SBE 38 Temperature Sensor. Most SBE 21s with serial number greater than 3110, & all SBE 21s with serial number greater than 3345 are compatible with SBE 38. See document 67119 for complete listing of parts.

Note: Order 50107 instead of 50298 for use with SBE 21 that has 3-pin bulkhead connector for remote temperature input — compatible with SBE 3 Temperature Sensor. All standard SBE 21s with serial number less than 3110 & some custom SBE 21s with serial number less than 3345 & greater than 3110 are compatible with SBE 3 Temperature Sensor. See document 67060 for complete listing of parts.
(Click here to see an example of where to find the serial number on your instrument.)

23388.2 SBE 21 top end cap blank (flow chamber seal when sensors removed) Seals flow chamber when electronics/sensor assembly removed from water jacket for recalibration/repair.
50315 Anti-foul holder kit - installs on SBE 4, & SeaCATs (not SeaCAT plus) to allow use of AF24173 in place of obsolete 24012 Anti-Foulant Devices. Order AF24173 separately

50315 provides fittings (2) to hold AF24173 Anti-Foulant Devices at each end of conductivity cell. See Application Note 70: Installing Anti-Foulant Device Mount Kit on SBE 4, 16, 19, and 21 Conductivity Cells.

  • SBE 21s shipped before 2002 used a smaller anti-foulant device inside Tygon tubing that attached to end of conductivity cell, & did not include 50315. For those SBE 21s, order 50315 & 801542 AF24173 Anti-Foulant Devices first time you need new Anti-Foulant Devices. Once you have 50315, order AF24173 Anti-Foulant Devices as needed.
  • SBE 21s shipped after 2002 include 50315 & 801542 installed on SBE 21. Order AF24173 Anti-Foulant Devices as needed.

  
50315 — slide Tygon on end of conductivity cell

801542 AF24173 Anti-Foulant Device pair (spare, bagged, labeled for shipping)
80438 Data I/O cable, RMG-4FS to 4-pin MS3106A connector, 10 m (DN 31063) Connects SBE 21 to 90488 SeaCAT / Sealogger RS-232 & Navigation Interface Box. Cable is included with standard shipment; this is spare.
90399.1 SBE 21 Electronics/sensor assembly (spare) (SBE 38 interface)

Fits inside water jacket. 90399.1 is for use with SBE 21 that is compatible with SBE 38 Temperature Sensor (standard SBE 21 with serial number > 3110 — supports input from remote SBE 38 thermometer through 4-pin remote temperature connector).

Note: Order PN 90387.1 instead for use with older SBE 21 that is compatible with SBE 3 Temperature Sensor — supports input from remote SBE 3 thermometer through 3-pin remote temperature connector.
(Click here to see an example of where to find the serial number on your instrument.)

23188.2 PVC water jacket/manifold assembly (no electronics or sensor housing) (spare) SBE 21 without 90399.1 (electronics/sensor assembly) pictured above.
171887 RS-232 serial cable, DB-9P to DB-9S, 3 m Connects Interface Box to computer. See 171887 for pinouts.
70271 Debubbler, Vortex, MSRC VDB-1, 3" diameter

Some installations require a de-bubbler. Click here for information on this de-bubbler, which is produced by the State University of New York, Ocean Instrument Laboratory.

 

Many cables, mount kits, and spare parts can be ordered online.

Cables

  • 17360 To SBE 3, 10 m, DN 30764
  • 171012 To SBE 38, 10 m, DN 31311
  • 17725 To ground, 4.6 m, DN 32280
  • 80437 To 90488, 90488.1, 90488.2, 90158.1, 90545, or 90204 SeaCAT/Sealogger RS-232 and Navigation Interface Box, 2.5 m, DN 31063
  • 80438 To 90488, 90488.1, 90488.2, 90158.1, 90545, or 90204 SeaCAT/Sealogger RS-232 and Navigation Interface Box, 10 m, DN 31063
  • 171887 To computer COM port (from 90488, 90488.1, 90488.2, 90158.1, 90545, or 90204 Interface Box) (replaces 801373, DN 32431)
  • 801424 To NMEA simulation computer COM port (from 90488, 90488.1, 90488.2, 90158.1, 90545, or 90204 Interface Box NMEA Input), 1.8 m, DN 32787
  • 17015 To AC power supply from 90488, 90158.1, or 90204 Interface Box (U.S. Standard)

Note: PN 90488.2 is current AC-powered Interface Box; PN 90488.1, 90488, and 90158.1 are older AC-powered Interface Boxes.
PN 90545 is current DC-powered Interface Box; PN 90204 is an older DC-powered Interface Box.

Mount Kits

  • For SBE 38 on seawater intake pipe leading to) SBE 21
    50244 Thermosalinograph Stainless Remote Temperature Sensor Mount Kit (document 67071)
  • For SBE 3S on seawater intake pipe leading to) SBE 21
    80403 Thermosalinograph Stainless Remote Temperature Sensor Mount Kit (document 67040)

Note: SBE 21 with serial number > 3110 is compatible with SBE 38; SBE 21 with serial number < 3110 is compatible with SBE 3S. (Click here to see an example of where to find the serial number on your instrument.)

Spare Parts

  • 801542 AF24173 Anti-Foulant Device (pair, bagged, labeled for shipping)
  • 50315 Anti-foul holder kit -- installs on SBE 4 & SeaCATs (not SeaCATplus) to allow use of AF24173 in place of obsolete 24012 Anti-Foulant Devices. Order AF24173 separately. For SBE 21s shipped before 2002. (see Application Note 70)
  • 50106 Hardware & O-ring kit for SBE 21 (document 67021)
  • 50092 Jackscrew kit for SBE 16, 17plus, 19, 21, 25, 26/26plus, 52-MP, 53, 54, AFM, or PDIM
  • 50298 Support kit for SBE 21 compatible with SBE 38 remote temperature sensor (hardware, O-rings connectors, cell cleaning supplies, etc.) (document 67119)
  • 50107 Support kit for SBE 21 compatible with SBE 3 remote temperature sensor (hardware, O-rings, connectors, cell cleaning supplies, etc.) (document 67060)
  • 23388.2 SBE 21 top end cap blank (flow chamber seal when sensors removed)
  • 90399.1 SBE 21 electronics/sensor assembly (SBE 38 interface)
  • 90387.1 SBE 21 electronics/sensor assembly (SBE 3 interface)
  • 23188.2 PVC water jacket/manifold assembly (no electronics or sensor housing

Note: SBE 21 with serial number > 3110 is compatible with SBE 38; SBE 21 with serial number < 3110 is compatible with SBE 3S. (Click here to see an example of where to find the serial number on your instrument.)

Compare Shipboard Thermosalinographs (Conductivity & Temperature)

SBE Measures Auxiliary
A/D Sensors
Recommended
Flow Rate
(cc/sec)
Remote Temperature
Sensor Input
NMEA
Data Input
Memory Power Communication Real-Time Data
Internal External
SBE 21 SeaCAT Thermosalinograph T, C 4 1000 64 Mb    RS-232
SBE 45 MicroTSG Thermosalinograph T, C   10-30 * *     RS-232
C = conductivity, T = temperature
* With optional PN 90402 SBE 45 Power, Navigation, and Remote Temperature Interface Box