Frequently Asked Questions (FAQs) --
Recommended Practices
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?
- 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?
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:
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.
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.
Remove the soaker tubes from the conductivity cells.
Remove any other sensor covers.
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.
Start SEASAVE. Set up a fixed display. Set number of scans to average to 24, and de-select store on disk. Start acquisition and view the data to verify the system is operational.
Clean optical sensor windows, and perform any required air calibration.
Stop acquisition. Do Not turn the CTD Deck Unit off. Select store on disk, and set number of scans to average to 1. Set up the plot scales and status line.
5 minutes before Station:
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.
Fill out any parts of the cast log that can be done at this time.
On Station, On Deck:
Verify the position and the bottom depth.
The computer operator should begin filling out the software header.
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.
Position the CTD under the block. Have the winchman remove any slack from the wire.
Notify the computer room that the CTD is ready for launch. The computer room should start acquiring data.
Obtain a barometric pressure reading and note it on the cast sheet.
When the bridge, computer room, and winchman are ready (and you have permission to proceed), put the CTD in the water.
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:
Finish filling out the cast log. Re-check the bottom depth.
Fill out the computer software log.
Hold the CTD at the surface for at least 3 minutes.
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:
Call the winchman and have him start the cast down. Typical lowering speed is 1 m/sec, modified for conditions as needed.
Watch the computer output and verify that the system is working.
During the Cast:
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.
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.
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:
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.
Adjust these numbers and procedures as conditions dictate to avoid crashing the CTD into the bottom.
When the CTD reaches the maximum cast depth, call the winchman and stop the descent.
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.
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:
As the CTD approaches the surface, have someone help spot for the winchman. Stop the CTD below the surface. Close a bottle if desired.
When ready, recover the CTD. Avoid banging the system against the ship.
CTD Back on Board:
Stop data acquisition and power off the CTD.
Move the CTD it into its holding area and secure it.
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.
See Application Note 64: SBE 43 Dissolved Oxygen Sensor for details on rinsing, cleaning, and storing oxygen sensors.
Rinse any optical sensors.
Rinse the SBE 32 Carousel latches with clean water.
Draw water samples from the bottles.
After the Cast:
Re-plot the data and look at any channels that were not displayed in real time.
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.
Final processing may need to wait until bottle salts and post-cruise lab calibrations are available.
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.
Application Note 83: Deployment of Moored Instruments contains a check list to assist users in deploying moored instruments. This checklist 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: I/O Connector Care and Installation describes the proper care and installation of standard connectors for Sea-Bird instruments. Once properly installed, the connections require minimal care. Unless access to the bulkhead is required, the connections can be left in place indefinitely. The Application Note covers connector cleaning and 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:
Thoroughly clean the connector with water, followed by alcohol.
Give the connector surfaces a light coating of silicon grease.
Re-mate the connectors properly ‑ see Application Note 57: I/O Connector Care and Installation.
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.
Remove any water from the o-rings and mating surfaces with a lint-free cloth or tissue.
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.
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.
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.
Video of
application of lubricant to o-ring.
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:
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 and 9plus) when removing them for shipment to Sea-Bird for calibration. See Removing Temperature and Conductivity Sensors for Calibration 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.
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, and 37), thermosalinographs (SBE 21 and 45), moored profilers (SBE 52-MP), and drifters (ALACE floats), and optionally with SBE 19plus and 49 profilers.
Useful 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.
Handling:
Refer to the Material Safety Data Sheet, enclosed with the shipment and available on our MSDS page, for details.
Anti-Foulant Devices are not classified by the U.S. DOT or the IATA as hazardous material.
There are several considerations to weigh when contemplating deployments in frazil or pancake ice and at low temperatures in general:
For accurate measurements, ice must be kept 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 will be 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. Keeping ice out of a competitor’s inductive cell (donut-shaped) would be more difficult because the volume to be protected is much larger (several cell diameters -- typically 20 cm) and the sensor will be as susceptible to instability resulting from any change in position of the mesh as to ice itself.
It is an essential fact that the conductivity cell must be made of some rigid material (glass, ceramic, or ‑ less ideally ‑ plastic). This rigidity is necessary because the measured conductivity is proportional to the geometry of the water sensed by the cell (basically the length-to-area ratio of the path of the electrical current flow). Because the cell is rigid, if water freezes in the cell it will almost certainly break (and thus destroy) the cell.
The above considerations apply to all known conductivity sensor types, whether electrode or inductive types. Large numbers of Sea-Bird conductivity instruments have been used in Arctic and Antarctic programs. In general, neither the accuracy of the temperature measurement nor the survival of the temperature sensor will be affected by ice.
Some additional recommendations in deploying a Sea-Bird conductivity sensor when there is any chance of freezing:
Transport and store the conductivity cell dry at high latitude, to keep the cell from cracking. Sea-Bird stores conductivity cells dry with no obvious effect on calibration drift. When stored dry, the electrodes require a short soaking in seawater to become fully wetted. This takes about 10-20 minutes (very mild agitation helps), and the full error due to non-wetted electrodes is 0.010 to 0.020 in salinity.
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. 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.
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 sensors (SBE 37-SIP, 37-SMP, 37-IMP, and 49) 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.
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:
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.
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:
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.
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.
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. Disconnect the pump cable for the test.
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.
Last modified: 06 Apr 2007
Sea-Bird Home Phone: 425-643-9866 Fax: 425-643-9954 E-mail: seabird@seabird.com
