Frequently Asked Questions (FAQs) --
FAQs have been organized into the following categories:
|Recommended practices (this page)|
- What are the major steps involved in taking a cast with a Profiling CTD?
- Should I collect water samples on the downcast or the upcast?
- Can I deploy my profiling CTD for monitoring an oil spill?
- What are the major steps involved in deploying a moored instrument?
- What are the recommended practices for mating and unmating connectors?
- How can I tell if my connectors have leaked, and what do I do about corrosion on connector pins?
- What are the recommended practices for replacing a bulkhead connector?
- What are the recommended practices for inspecting and cleaning o-rings and mating surfaces?
- How often should I replace o-rings?
- How should I handle my CTD to avoid cracking the conductivity cell?
- What is an Anti-Foulant Device? How often should I replace it? Does it require special handling?
- What are the recommended practices for deploying in frazil or pancake ice, or deploying at low temperatures?
- Does it matter if I deploy my moored instrument, which includes a conductivity sensor, in a horizontal or vertical position?
- How many / what kind of spares should I have on ship for my instrument?
- How many/what kind of spares should I have on ship for my SBE 9plus?
- How will my CTD be affected by adjacent objects?
- What are the safety concerns/procedures if the instrument floods? Can the instrument explode?
- Is it necessary to put my instrument in water to test it? Will I destroy the conductivity cell if I test it in air?
- How should I store my conductivity sensor if there is danger of freezing?
- What are the recommended practices for cleaning and lubricating winch cables?
- What are the recommended practices for splicing cables?
|General instrument questions
|General oceanographic questions
|Data analysis and processing
Our Glossary page is another good source of information.
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:
5 minutes before Station:
On Station, On Deck:
CTD Soaking at the Surface:
Starting the Cast:
During the Cast:
Approaching the Bottom:
End of the Cast:
CTD Back on Board:
After the Cast:
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.
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:
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.
After each recovery, rigorously follow the cleaning and storage procedures in the following application notes ‑
Quick Reference Sheets for Oil Spill Deployment:
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.
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.
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:
Re-mate the connectors properly ‑ see Application Note 57: Connector Care and Cable Installation and nine-minute video covering O-ring, connector, and cable maintenance.
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).
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.
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:
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.
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-SIP-ODO, 37-IM, 37-IMP, 37-IMP-IDO, 37-IMP-ODO), thermosalinographs (SBE 21 and 45), moored profilers (SBE 52-MP), and drifters (SBE 41/41CP Argo float CTDs), and optionally with SBE 19plus, 19plus V2, and 49 profilers.
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.
Shelf Life and Storage: The best way to store Anti-Foulant Devices is in an air-tight 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.
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.
There are several considerations to weigh when contemplating deployments in frazil or pancake ice and at low temperatures in general:
The above considerations apply to all known conductivity sensor types, whether electrode or inductive types.
Some additional recommendations in deploying a Sea-Bird conductivity sensor when there is any chance of freezing:
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.
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.
In general, neither the accuracy of the temperature measurement nor the survival of the temperature sensor will be affected by ice.
For the SBE 43 Dissolved Oxygen sensor, avoid prolonged exposure to freezing temperature, including during shipment. Do not store the SBE 43 with water (fresh or seawater), Triton solution, alcohol, or glycol in the plenum. The best precaution is to keep the SBE 43 indoors or in some shelter out of the cold weather.
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-SIP, 37-SIP-IDO, 37-SIP-ODO, 37-SMP, 37-SMP-IDO, 37-SMP-ODO, 37-IMP, 37-IMP-IDO, 37-IMP-ODO) have a required orientation because of their u-shaped plumbing configuration. Refer to the instrument manual for details.
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 the question below for spares recommendations specific to the 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.
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:
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:
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:
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.
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.
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.
When CTDs are exposed to deck temperatures consistently below freezing an additional concern needs to be addressed. On deployment, parts of the CTD that are colder than the freezing point of seawater will form a thin layer of ice. If ice forms inside the conductivity cell, then 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. Special accommodation to keep temperature, conductivity, oxygen, and optical sensors at or above 0 °C is advised. Often at high latitude the CTD is brought inside protective doors between casts to achieve this.
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.
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. Click here to 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.
Last modified: 16 May 2013
Sea-Bird Home Phone: (+1) 425-643-9866 Fax: (+1) 425-643-9954 E-mail: email@example.com