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

Moored Conductivity, Temperature, (optional) Pressure, and Optical Dissolved Oxygen measurements at user-programmable intervals. RS-232, RS-485 interface and internal memory; powered externally.

Coming soon!


Compare features of the numerous SBE 37 MicroCAT models.

Conductivity 0 to 7 S/m
(0 to 70 mS/cm)
± 0.0003 S/m
(0.003 mS/cm)
0.0003 S/m
(0.003 mS/cm)
per month
0.00001 S/m
(0.0001 mS/cm)
-5 to 45 ± 0.002
(-5 to 35 °C);
± 0.01
(35 to 45 °C)
per month
20 / 100 / 350 /
600 / 1000 / 2000 /
3500 / 7000 m
(meters of
deployment depth capability)
± 0.1% of
full scale range
0.05% of
full scale range
per year
0.002% of
full scale range


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

Title Type Publication Date PDF File
SBE Data Processing Manual Software Manual Friday, December 8, 2017 SBEDataProcessing_7.26.7.pdf
AN06: Determination of Sound Velocity from CTD Data Application Notes Tuesday, February 2, 2010 appnote06Aug04.pdf
AN10: Compressibility Compensation of Sea-Bird Conductivity Sensors Application Notes Tuesday, May 7, 2013 appnote10May13.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
AN42: ITS-90 Temperature Scale Application Notes Wednesday, May 18, 2016 appnote42May16.pdf
AN52: AC Powered Opto-Isolated RS-485 to RS-232 Junction Box P/N 80491 Instructions for Application and Use Application Notes Tuesday, February 9, 2010 appnote52Feb10.pdf
AN56: Interfacing to RS-485 Sensors Application Notes Wednesday, February 11, 2009 appnote56Feb09.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
AN69: Conversion of Pressure to Depth Application Notes Monday, July 1, 2002 appnote69.pdf
AN73: Using Instruments with Pressure Sensors at Elevations Above Sea Level Application Notes Wednesday, April 12, 2017 appnote73Apr17.pdf
AN90: Absolute Salinity and TEOS-10: Sea-Bird's Implementation Application Notes Tuesday, September 3, 2013 AppNote90Sep13.pdf
SeatermV2© is a terminal program launcher for setup and data upload of Sea-Bird instruments developed or redesigned in 2006 and later. The common feature of this generation of instruments is the ability to output status responses in XML. SeatermV2 is part of our Seasoft V2 software suite.
Version 2.6.3 released July 26, 2017
SeatermV2.6.3-b19.exe for Windows 7/8/10

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 7.26.7 released July 26, 2017

Please Note:

Seasoft V2 is a single install bundle with the following stand-alone programs (table below) for use with most of our products (especially SBE numbers products like SBE 37 MicroCATs). While most of our instruments uses one or more of these programs, not all instruments use all programs (eg.  Plot39 which is only used by SBE 39 family) .

Each instrument has the list of applicable programs under the product page's software tab. Each software includes Help files with detailed descriptions for use.

Version 2.2.7 released July 26, 2017
SeasoftV2.2.7-b19.exe for Windows 7/8/10

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.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Conductivity cells are made of glass, which is breakable.

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

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

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

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

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

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

Mating and Unmating Connectors:

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

Checking for Leakage and Cleaning Corrosion on Connectors:

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

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

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

Replacing Connectors:

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

What are the recommended practices for 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.

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

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

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

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

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

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

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

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

Can I use a pressure sensor above its rated pressure?

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

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

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

What is the 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, 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.

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, many 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 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

Family Model . Housing Pressure Sensor/Range Connectors Communications SBE 63 Optical
Dissolved Oxygen
37 SIP . 1 – 350 m (plastic) 0 – none 1 – XSG 0 – RS-232 2 – 600 m
      2 – 7000 m (titanium) 1 – 20 m strain gauge 2 – MCBH 1 – RS-485 3 – 5000 m
        2 – 100 m strain gauge     4 – 7000 m
        3 – 350 m strain gauge      
        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      

Example: 37SIP.13102 is an SBE 37-SIP-ODO with 350 m housing, 350 m strain gauge pressure sensor, XSG connector, RS-232 communications, and integrated SBE 63 Optical Dissolved Oxygen Sensor with DO sensor rated to 600 m. See table below for description of each selection:


MicroCAT C and T (pressure optional) Sensor with Integrated SBE 63 Optical Dissolved Oxygen sensor (ODO), Serial interface and Internal Pump - Includes 8 MB Flash memory, serial interface, data/power cable (cable may be deleted for credit), AF24173 Anti-Foulant Devices, Seasoft software, & complete documentation.

37-SIP-ODO MicroCAT includes:

  • Serial Interface
  • Memory
  • internal, integral Pump
  • integrated Optical Dissolved Oxygen sensor

Note: 37-SIP-ODO does not include internal batteries.

Compare features of the numerous SBE 37 MicroCAT models.

SBE 37-SIP-ODO Housing (depth) Selections MUST SELECT ONE
37SIP.1xxxx 350 m plastic housing  
37SIP.2xxxx 7000 m titanium housing  
SBE 37-SIP-ODO Pressure Sensor Range (depth) Selections MUST SELECT ONE
37SIP.x0xxx No pressure sensor Pressure sensor is installed in end cap (behind mount clamp), & is not field replaceable / swappable. While highest pressure rating gives you most flexibility in using MicroCAT, 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)
37SIP.x1xxx 20 m strain gauge pressure sensor
37SIP.x2xxx 100 m strain gauge pressure sensor
37SIP.x3xxx 350 m strain gauge pressure sensor
37SIP.x4xxx 600 m strain gauge pressure sensor
37SIP.x5xxx 1000 m strain gauge pressure sensor
37SIP.x6xxx 2000 m strain gauge pressure sensor
37SIP.x7xxx 3500 m strain gauge pressure sensor
37SIP.x8xxx 7000 m strain gauge pressure sensor
SBE 37-SIP-ODO Connector Selections MUST SELECT ONE
37SIP.xx1xx XSG connector (includes data/power interface cable 801385)

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.

XSG connector on left, Wet-pluggable (MCBH) connector on right

37SIP.xx2xx Wet-pluggable (MCBH) connector (includes data/power interface cable 801206)
SBE 37-SIP-ODO Communications Selections MUST SELECT ONE
37SIP.xxx0x RS-232 serial interface Note: Each interface version of 37-SIP-ODO has a separate manual.
37SIP.xxx1x RS-485 (half duplex ONLY) serial interface Two-wire, RS-485 interface provides communication with individual 37-SIP-ODO or with all 37-SIP-ODOs attached to RS-485 interface. This allows for coordination of sampling among many instruments. However, note that half-duplex communication is one-direction at a time (i.e., you cannot send commands & receive data at same time).
Note: Each interface version of 37-SIP-ODO has a separate manual.
SBE 37-SIP-ODO Optical Dissolved Oxygen Sensor Selections MUST SELECT ONE
37SIP.xxxx2 600 meter  
37SIP.xxxx3 5000 meter
37SIP.xxxx4 7000 meter
SBE 37-SIP-ODO Mooring Clamp Wire Size Selections (Specify clamp to match O.D. of mooring wire jacket) — MUST SELECT ONE
37SIP-4a Plastic brackets to provide through-bolt mounting to a flat surface See document 67218
37SIP-4b Wire guide & mounting clamp for 1/4 in. diameter mooring wire

37-SMP-IDO shown; mooring clamp detail for 37-SIP-ODO identical

Cable fits loosely through wire guide, & is clamped only at mounting clamp. See document67219.

Thread for clamping to mooring cable:

  • 37SIP-1a (1/4 in. diameter): 1/4-28 UNF
  • 37SIP-1b (5/16 in. diameter): 5/16-24 UNF
  • 37SIP-1c (3/8 in. diameter): 3/8-24 UNF
  • 37SIP-1d (1/2 in. diameter): 9/16-12 UNC
  • 37SIP-1e (6 mm diameter): 1/4-20 UNF
  • 37SIP-1f (8 mm diameter): 5/16-24 UNF
  • 37SIP-1g (10 mm diameter): 7/16 -14 UNF
  • 37SIP-1h (12 mm diameter): 1/2-13 UNF
  • 37SIP-1i (16 mm, 5/8 in. diameter): 5/8-18 UNF
37SIP-4c Wire guide & mounting clamp for 5/16 in. diameter mooring wire
37SIP-4d Wire guide & mounting clamp for 3/8 in. diameter mooring wire
37SIP-4e Wire guide & mounting clamp for 1/2 in. diameter mooring wire
37SIP-4f Wire guide & mounting clamp for 6 mm diameter mooring wire
37SIP-4g Wire guide & mounting clamp for 8 mm diameter mooring wire
37SIP-4h Wire guide & mounting clamp for 10 mm diameter mooring wire
37SIP-4i Wire guide & mounting clamp for 12 mm diameter mooring wire
37SIP-4j Wire guide & mounting clamp for 16 mm (5/8 in.) diameter mooring wire
SBE 37-SIP-ODO Storm Shipping Case Option - holds up to 3 SBE 37SIP-ODOs
37SIP-6I Storm Shipping Case (iM2950) instead of wood crate - holds up to 3 SBE 37SIP-ODOs

Case holds only 3 ODO MicroCATs
(photo shows 4 non-ODO MicroCATs

Storm shipping case with custom foam inserts holds up to 3 ODO MicroCATs — IMP-ODO, SMP-ODO, SIP-ODO.

  • Injection molded case with HPX resin plastic body, recessed wheels, automatic pressure equalization valve, hinged push-button latches, fold-down padded handle, & O-ring seal. Meets airline luggage regulations.
  • Inner dimensions:
    29 x 18 x 10.5 inches (74 x 46 x 27 cm).
  • Outer dimensions:
    31.3 x 20.4 x 12.2 inches (80 x 52 x 31 cm).

Price for 37SIP-6I reflects a credit for deletion of our standard wood crate.

SBE 37-SIP-ODO 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.
801376 Data/Power interface cable, RMG-4FS to DB-9S & 9V battery snap, 2.4 m (DN 32604) Some users prefer battery snap connector instead of red/black twisted wire leads. Order 801376 in place of 801385 if desired.
801263 Data/Power interface cable, Wet-Pluggable, MCIL-4FS to DB-9S & 9V battery snap, 2.4 m (DN 32490) Some users prefer battery snap connector instead of red/black twisted wire leads. Order 801263 in place of 801206 if desired.
801385 Data/Power interface cable, RMG-4FS to DB-9S & red/black twisted wire leads, 2.4 m (DN 32277) Included with standard shipment if 37SIP.xx1xx (XSG connector) selected; this is spare.
801206 Data/Power interface cable, Wet-Pluggable, MCIL-4FS to DB-9S & red/black twisted wire leads, 2.4 m (DN 32366) Included with standard shipment if 37SIP.xx2xx (MCBH connector) selected; this is spare.
801378 Data / Power interface cable, shielded, RMG-4FS to DB-9S & red/black twisted wire leads, 20 m (DN 32720) Longer, shielded cable for use if if 37SIP.xx1xx (XSG connector) selected.
20200 USB to Serial Port Adapter, FTDI UC232R-10 (connects computers with USB ports to RS-232 instruments) Many newer PCs & laptop computers have USB port(s) instead of RS-232 serial port(s). USB serial adapter plugs into USB port, & allows a serial device to be connected through adapter. Multi-port adapters are available from other companies; see Application Note 68.
TBD Storm Shipping Case (iM2950) - holds up to 3 SBE 37SIP-ODOs

Case holds only 3 ODO MicroCATs
(photo shows 4 non-ODO MicroCATs)

Storm shipping case with custom foam inserts holds up to 3 ODO MicroCATs — IMP-ODO, SMP-ODO, SIP-ODO.

  • Injection molded case with HPX resin plastic body, recessed wheels, automatic pressure equalization valve, hinged push-button latches, fold-down padded handle, & O-ring seal. Meets airline luggage regulations.
  • Inner dimensions:
    29 x 18 x 10.5 inches (74 x 46 x 27 cm).
  • Outer dimensions:
    31.3 x 20.4 x 12.2 inches (80 x 52 x 31 cm).



  • 801385 To computer COM port with power leads (from XSG connector), 2.4 m, DN 32277
  • 801376 To computer COM port with 9V connector (from XSG connector), 2.4 m, DN 32604
  • 801206 To computer COM port with power leads (from Wet-pluggable connector), 2.4 m, DN 32366
  • 801263 To computer COM port with 9V connector (from Wet-pluggable connector), 2.4 m, DN 32490
  • 801378 To computer COM port with power leads (from XSG connector), shielded, 20 m, DN 32720

Mount Kits

Mounted to Flat Surface

  • 50479 SBE 37-SMP-IDO or 37-SIP-IDO Thru Bolt Mounting Clamp Kit (document 67218)

Mounted to Mooring Cable

(document 67219 for all sizes)

  • 50465  SBE 37-SMP or SIP Cable Clamp Kit, 1/4-inch diameter 
  • 50469  SBE 37-SMP or SIP Cable Clamp Kit, 5/16-inch diameter
  • 50470  SBE 37-SMP or SIP Cable Clamp Kit, 3/8-inch diameter
  • 50473  SBE 37-SMP or SIP Cable Clamp Kit, 1/2-inch diameter
  • 50467  SBE 37-SMP or SIP Cable Clamp Kit, 6-mm diameter
  • 50468  SBE 37-SMP or SIP Cable Clamp Kit, 7-mm diameter
  • 50471  SBE 37-SMP or SIP Cable Clamp Kit, 10-mm diameter
  • 50472  SBE 37-SMP or SIP Cable Clamp Kit, 11-mm diameter
  • 50474  SBE 37-SMP or SIP Cable Clamp Kit, 12-mm diameter
  • 50476  SBE 37-SMP or SIP Cable Clamp Kit, 16-mm (5/8-inch) diameter
  • 50478  SBE 37-SMP or SIP Cable Clamp Kit, 20-mm diameter

Spare Parts

Hardware & O-Ring Kits

  • 60060 Hardware & O-ring kit for SBE 37-SIP-IDO or SIP-ODO (document 67215)


  • 801542 AF24173 Anti-Foulant Device (pair, bagged, labeled for shipping)
  • TBD Storm shipping case (iM2950) — holds up to 3 IDO or ODO MicroCATs (photo of MicroCATs in this shipping case)