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SBE 52-MP with optional Dissolved Oxygen Sensor

SBE 52-MP Moored Profiler CTD & (optional) Dissolved Oxygen Sensor

Conductivity, Temperature, Pressure, optional Dissolved Oxygen, at 1 sample/sec (1 Hz). RS-232 or Logic Level interface, no batteries, small memory — for use on moored profiling vehicles that can supply power and acquire data.

52-MP on McLane Moored Profiler

The SBE 52-MP CTD sensor is intended for use as a modular component on moored profiling platforms in which a device travels vertically beneath a buoy or a buoyant package is winched up and down from a bottom-mounted platform. It is an easy-to-use, light, and compact instrument, well suited to even the smallest vehicle. The 52-MP can be equipped with an SBE 43F Dissolved Oxygen sensor, but does not support other auxiliary sensors. It is externally powered, and temporarily stores data in memory (if power is removed, data in memory is lost).

The SBE 52-MP’s pump-controlled, TC-ducted flow minimizes salinity spiking, and its 1 Hz sampling provides good resolution of oceanographic structures and gradients on typical slow-moving packages (20-50 cm/sec). Data are output in real-time in engineering units (mmho/cm, °C, decibars, ml/l) or raw hex or binary.


  • Conductivity, Temperature, Pressure, and (optional) Oxygen at 1 Hz (1 sample/second) or polled sample acquisition.
    - For 1 Hz sampling, SBE 52-MP stores data in memory and can also transmit in real-time. On command (typically at the end of each profile), data is uploaded to the moored profiler.
  • Integral pump.
  • RS-232 or logic-level (0-3.3 V) interface, small memory, no batteries — for use on vehicles that can supply power and acquire data.
  • Unique flow path, pumping regimen, and expendable anti-foulant devices, for maximum bio-fouling protection.
  • Pump-controlled, T-C ducted flow to minimize salinity spiking.
  • 3/8-16 locator/mounting hole, to assist in mounting to a McLane MMP moored profiler.
  • Depths to 600 or 7000 m.
  • Seasoft© V2 Windows software package (setup and data display).
  • Five-year limited warranty.


  • Unique internal-field conductivity cell 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.
  • Pressure sensor with temperature compensation is available in eight strain-gauge ranges (to 7000 m).
  • (optional) Oxygen sensor is field-proven, individually calibrated SBE 43F Dissolved Oxygen sensor.
  • For 1 Hz sampling, pump runs continuously, providing bio-fouling protection and correlation of CTD (and optional DO) measurements. For polled sampling, Adaptive Pump Control provides high-accuracy oxygen data.


  • Plastic (600 m) or titanium (7000 m) housing.
  • SBE 43F Dissolved Oxygen Sensor (frequency-output version of our SBE 43).
  • RS-232 or logic level (0 - 3.3 V) interface.
  • XSG/AG or wet-pluggable MCBH connectors.

Measurement Range

Conductivity 0 to 9 S/m (0 to 90 mmho/cm)
Temperature -5 to +35 °C
Pressure 0 to 20 / 100 / 350 / 600 / 1000 / 2000/ 3500 / 7000 m
Dissolved Oxygen (optional) 120% of surface saturation (all natural waters, fresh & salt)

Initial Accuracy

Conductivity ± 0.0003 S/m (0.003 mmho/cm)
Temperature ± 0.002 °C
Pressure ± 0.1% of full scale range
Dissolved Oxygen (optional) ± 2% of saturation

Typical Stability

Conductivity 0.0003 S/m (0.003 mmho/cm) per month
Temperature 0.0002 °C per month
Pressure 0.05% of full scale range per year
Dissolved Oxygen (optional) 0.5% per 1000 hours (clean membrane)


Conductivity 0.00005 S/m (most oceanic waters; 0.4 ppm in salinity)
Temperature 0.001 °C
Pressure 0.002% of full scale range
Dissolved Oxygen (optional) 0.035% of saturation (0.003 ml/l at 0 °C and 35 PSU)


Sampling Speed 1 Hz (1 sample/sec)
External Power Requirements Input power: 3 Watts at 7-16 VDC (consult factory for voltage outside this range)
Turn-on transient: 300 mA at 10V
Sampling (includes pump): 62 mA at 10 V
Memory Static RAM stores up to 28,000 samples of C, T, P, & DO (if power removed, data in memory is lost)
Housing, Depth Rating, & Weight Plastic, 600 m, in air 3.2 kg, in water 1.5 kg
3AL-2.5V Titanium, 7000 m, in air 5.3 kg, in water 3.7 kg


DO sensor cable not shown for clarity

The list below includes (as applicable) the current product brochure, manual, and quick guide; software manual(s); and application notes.

For older SBE 52-MP product manuals, organized by instrument firmware version, click here.

Title Type Publication Date PDF File
SBE 52-MP Datasheet Product Datasheet Monday, December 14, 2015 PDF icon 52brochureDec15.pdf
SBE 52-MP Manual Product Manual Wednesday, February 18, 2015 PDF icon 52_011.pdf
AN02D: Instructions for Care and Cleaning of Conductivity Cells Application Notes Monday, June 13, 2016 PDF icon appnote2DJun16.pdf
AN06: Determination of Sound Velocity from CTD Data Application Notes Tuesday, February 2, 2010 PDF icon appnote06Aug04.pdf
AN10: Compressibility Compensation of Sea-Bird Conductivity Sensors Application Notes Tuesday, May 7, 2013 PDF icon appnote10May13.pdf
AN14: 1978 Practical Salinity Scale Application Notes Thursday, January 12, 1989 PDF icon appnote14.pdf
AN27D: Minimizing Strain Gauge Pressure Sensor Errors Application Notes Wednesday, May 18, 2016 PDF icon appnote27DMay16.pdf
AN38: TC Duct Fundamentals Application Notes Tuesday, July 10, 2012 PDF icon appnote38Jul12.pdf
AN42: ITS-90 Temperature Scale Application Notes Wednesday, May 18, 2016 PDF icon appnote42May16.pdf
AN57: Connector Care and Cable Installation Application Notes Tuesday, May 13, 2014 PDF icon appnote57Jan14.pdf
AN68: Using USB Ports to Communicate with Sea-Bird Instruments Application Notes Friday, October 19, 2012 PDF icon appnote68Oct12.pdf
AN69: Conversion of Pressure to Depth Application Notes Monday, July 1, 2002 PDF icon appnote69.pdf
AN73: Using Instruments with Pressure Sensors at Elevations Above Sea Level Application Notes Wednesday, April 12, 2017 PDF icon appnote73Apr17.pdf
AN84: Using Instruments with Druck Pressure Sensors in Muddy or Biologically Productive Environments Application Notes Tuesday, January 14, 2014 PDF icon appnote84Jan14.pdf
AN98: Considerations for CTD Spatial and Temporal Resolution on Moving Platforms Application Notes Wednesday, July 5, 2017 PDF icon appnote98.pdf
Field Service Bulletin 13: Jackscrew Replacements Field Service Bulletins Monday, March 8, 2010 PDF icon FSB13.pdf

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


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 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.

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.

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, our 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 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.

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 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

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.
  • Moored CTD — recalibrate at least once/year, but possibly more often depending on the degree of bio-fouling in the water.
  • 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.

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 or similar scrubbing device.

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 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.

Family . Housing Pressure Sensor/Range Connector Communications Oxygen Sensor
52 . 1 – 600 m (plastic) 1 – 20 m strain gauge 1 – XSG 1 – RS-232 0 – None
    3 – 7000 m (titanium) 2 – 100 m strain gauge 2 – MCBH 2 – Logic Level Serial 1 – 600 m
      3 – 350 m strain gauge     2 – 7000 m
      4 – 600 m strain gauge      
      5 – 1000 m strain gauge      
      6 – 2000 m strain gauge      
      7 – 3500 m strain gauge      
      8 – 7000 m strain gauge      



Moored Profiler CTD - RS-232 or logic level serial interface, AF24173 Anti-Foulant Devices, 2.4 m data/power interface cable (801385), Seasoft software, & complete documentation.

SBE 52-MP is a CTD (conductivity, temperature, depth [pressure] ) sensor designed for making vertical profile measurements while integrated with a moored profiler below a buoy; typically, some form of tractor device moves moored profiler up & down along mooring wire. SBE 52-MP comes standard with electronics & bulkhead connector for interfacing with a dissolved oxygen sensor; dissolved oxygen sensor is an option (see below).

SBE 52-MP Housing (depth) Selections MUST SELECT ONE
52.1xxxx 600 m plastic housing  
52.3xxxx 7,000 m plastic housing  
SBE 52-MP Pressure Sensor Range (Depth) Selections MUST SELECT ONE
52.x1xxx 20 m strain gauge pressure sensor Pressure sensor is installed in connector end cap, & is not field replaceable / swappable. While highest pressure rating gives you most flexibility in using 52-MP, it is at expense of accuracy & resolution. It is advantageous to use lowest range pressure sensor compatible with your intended maximum operating depth, because accuracy & resolution are proportional to pressure sensor's full scale range. For example, comparing 2000 & 7000 m sensors:
  • 2000 m sensor:
    initial accuracy = 2 m (= 0.1% * 2000 m),
    resolution = 0.04 m (= 0.002% * 2000 m)
  • 7000 m sensor:
    initial accuracy = 7 m (= 0.1% * 7000 m),
    resolution = 0.14 m (= 0.002% * 7000 m)
52.x2xxx 100 m strain gauge pressure sensor
52.x3xxx 350 m strain gauge pressure sensor
52.x4xxx 600 m strain gauge pressure sensor
52.x5xxx 1000 m strain gauge pressure sensor
52.x6xxx 2000 m strain gauge pressure sensor
52.x7xxx 3500 m strain gauge pressure sensor
52.x8xxx 7000 m strain gauge pressure sensor
SBE 52-MP  Connector Selections MUST SELECT ONE

XSG/RMG connectors on instrument & data I/O cable

Wet-pluggable connectors may be mated in wet conditions. Their pins do not need to be dried before mating. By design, water on connector pins is forced out as 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 XSG/AG connectors. Like XSG/AG connectors, wet-pluggables need proper lubrication & require care during use to avoid trapping water in sockets.


Wet-pluggable (MCBH) connectors on instrument & data I/O cable

SBE 52-MP Communication Selections MUST SELECT ONE
52.xxx1x RS-232 Serial Interface Serial interface is set with jumpers on SBE 52-MP electronics.
52.xxx2x Logic Level Serial Interface (0-3.3v)
SBE 52-MP Dissolved Oxygen Selections MUST SELECT ONE
52.xxxx0 No oxygen sensor  


Integrate 600 m SBE 43F Dissolved Oxygen Sensor

SBE 43F is a frequency output version of our SBE 43 Dissolved Oxygen Sensor, & has same performance specifications. Select depth rating for SBE 43F compatible with depth rating of your instrument housing.


Integrate 7000 m SBE 43F Dissolved Oxygen Sensor

SBE 52-MP Spares & Accessories
801542 AF24173 Anti-Foulant Device pair (spare, bagged, labeled for shipping) Anti-foulant devices fit into anti-foulant device cups at each end of conductivity cell. Anti-foulant devices included with standard shipment; these are spares.
Useful life varies, depending on several factors. We recommend that customers consider more frequent replacement when high biological activity & strong current flow (greater dilution of anti-foulant concentration) are present. Moored instruments in high growth & 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 strongest determining factor in specific deployment environments.
17031 4-pin pigtail cable, RMG-4FS with lock sleeve, 2.4 m (DN 30581) These cables are for interfacing with your system's controller. Applicable cable (RMG or wet-pluggable connector) is included with SBE 52-MP; these are spares.
171368 4-pin pigtail cable, Wet-Pluggable, MCIL-4FS w/MCDSL-F, 2.4 m (DN 32363)
171558 Cable, SBE 43F, IE55 3-pin to 3-pin, 0.5 m (DN 32561) This cable is for connecting optional SBE 43F to standard IE-55 bulkhead connector on SBE 52-MP. Cable is included with SBE 52-MP if ordered with oxygen sensor; this is spare.


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


  • 17031pigtail (from XSG connector), 2.4 m, DN 30581
  • 801385 To computer COM port with power leads (from XSG connector), 2.4 m, DN 32277
  • 171368 pigtail (from Wet-pluggable connector), 2.4 m, DN 32363
  • 801206 To computer COM port with power leads (from Wet-pluggable connector), 2.4 m, DN 32366
  • 171558 To dissolved oxygen sensor, 0.53 m, DN 32561

Spare Parts

  • 50092 Jackscrew kit for SBE 16, 17plus, 19, 21, 25, 26/26plus, 52-MP, 53, 54, AFM, or PDIM
  • 801542 AF24173 Anti-Foulant Device (pair, bagged, labeled for shipping)
  • 50312 Anti-foulant device in-line cap/cup assembly for SBE 49 or 52-MP (document 67123)
  • 233186 High-head pressure port plug for muddy/biologically productive environments (Application Note 84)

Compare  Moored / Time Series Recording Instruments

SBE Measures
(C, T, P)
Auxiliary Sensors Memory Power Communication Real-Time
Internal External
SBE 16plus V2 SeaCAT C-T (P) Recorder C, T, P* 6 A/D; 1 RS-232 64 Mb RS-232 Optional pump
SBE 16plus SeaCAT C-T (P) Recorder
C, T, P* 4 A/D; optional RS-232 or PAR 8 Mb RS-232 or -485 Replaced by SBE 16plus V2 in 2008
SBE 16 SeaCAT C-T (P) Recorder
C, T, P* 4 A/D 1 Mb RS-232 Replaced by SBE 16plus in 2001
SBE 16plus-IM V2 SeaCAT C-T (P) Recorder C, T, P* 6 A/D; 1 RS-232 64 Mb   Inductive Modem Optional pump
SBE 16plus-IM SeaCAT C-T (P) Recorder
C, T, P* 4 A/D; optional RS-232 or PAR 8 Mb   Inductive Modem Replaced by SBE 16plus-IM V2 in 2008
SBE 19plus V2 SeaCAT Profiler CTD C, T, P 6 A/D; 
1 RS-232
64 Mb RS-232 Programmable mode — profiling or moored
SBE 19plus SeaCAT Profiler CTD
C, T, P 4 A/D; optional PAR 8 Mb RS-232 Replaced by SBE 19plus V2 in 2008
SBE 19 SeaCAT Profiler CTD
C, T, P 4 A/D 1 - 8 Mb RS-232 Replaced by SBE 19plus in 2001
SBE 37-SM MicroCAT C-T (P) Recorder C, T, P*   8 Mb RS-232 or -485  
SBE 37-SMP MicroCAT C-T (P) Recorder C, T, P*   8 Mb RS-232, RS-485, or SDI-12 Integral pump
SBE 37-SMP-IDO MicroCAT C-T-DO (P) Recorder C, T, P* Integrated DO 8 Mb RS-232 or -485 Integral pump; Replaced by SBE 37-SMP-ODO in 2014
SBE 37-SMP-ODO MicroCAT C-T-DO (P) Recorder C, T, P* Integrated Optical DO 8 Mb RS-232, RS-485, or SDI-12 Integral pump
HydroCAT C-T-(DO)-(P) Recorder C, T, P* Integrated Optical DO* 8 Mb RS-232 & SDI-12 Integral pump; for Coastal applications to 350 m
C-T-pH-(DO)-(P)-(Chl)-(NTU) Recorder
C, T, P* Integrated pH, Optical DO*, Chlorophyll*, Turbidity* 16 Mb RS-232 & SDI-12 Integral pump; for Coastal applications to 350 m
SeapHOx Ocean C-T-DO-pH (P) Recorder C, T, P* Integrated Optical DO, pH 8 Mb RS-232 37-SMP-ODO with SeaFET pH sensor; to 50 m
Deep SeapHOx Ocean C-T-DO-pH (P) Recorder C, T, P* Integrated Optical DO, pH 8 Mb RS-232 37-SMP-ODO with Deep SeaFET pH sensor; to 2000 m
SBE 37-IM MicroCAT C-T (P) Recorder C, T, P*   8 Mb   Inductive modem  
SBE 37-IMP MicroCAT C-T (P) Recorder C, T, P*   8 Mb   Inductive modem Integral pump
SBE 37-IMP-IDO MicroCAT C-T-DO (P) Recorder C, T, P* Integrated DO 8 Mb   Inductive modem Integral pump; Replaced by SBE 37-IMP-ODO in 2014
SBE 37-IMP-ODO MicroCAT C-T-DO (P) Recorder C, T, P* Integrated Optical DO 8 Mb   Inductive modem Integral pump
SBE 37-SI MicroCAT C-T (P) Recorder C, T, P*   8 Mb   RS-232 or -485  
SBE 37-SIP MicroCAT C-T (P) Recorder C, T, P*   8 Mb   RS-232 or -485 Integral pump

SBE 37-SIP-IDO MicroCAT C-T-DO (P) Sensor

C, T, P* Integrated DO 8 Mb   RS-232 or -485 Integral pump
SBE 39plus Temperature (P) Recorder T, P*   64 Mb Optional USB & RS-232 Optional  
SBE 39 Temperature (P) Recorder
T, P*   32 Mb Optional RS-232 Optional Replaced by SBE 39plus in 2014
SBE 39plus-IM Temperature (P) Recorder T, P*   64 Mb   Inductive Modem & USB  
SBE 39-IM Temperature (P) Recorder T, P*   32 Mb   Inductive modem Replaced by SBE 39plus-IM in 2016
SBE 56 Temperature Logger T   64 Mb   USB    
SBE 26plus Seagauge Wave & Tide Recorder T, P C optional 32 Mb RS-232
(tides, waves, & wave statistics)
Wave & tide recorder
SBE 26 Seagauge Wave & Tide Recorder
T, P C optional 8 Mb RS-232   Replaced by SBE 26plus in 2004
SBE 53 BPR Bottom Pressure Recorder T, P C optional 32 Mb RS-232 Bottom pressure recorder
SBE 54 Tsunameter Tsunami Pressure Sensor T, P   128 Mb Optional RS-232 Tsunami pressure sensor

C = conductivity, T = temperature, P = pressure, DO = dissolved oxygen
* = optional
products are no longer in production. Follow the links above to the product page to retrieve manuals and application notes for these older products.