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SBE 43

SBE 43 Dissolved Oxygen Sensor

Membrane-type, fast-response oxygen sensor with voltage output, for integration with profiling or moored CTDs. For use in CTD pumped flow path.

The SBE 43 is an individually calibrated, high-accuracy oxygen sensor to assist in critical hypoxia and ocean stoichiometric oxygen chemistry research on a variety of profiling and moored platforms. Careful choices of materials, geometry, and sensor chemistry are combined with superior electronics and calibration methodology to yield significant gains in performance.

The SBE 43 is designed for use in a CTD’s pumped flow path, providing optimal correlation with CTD measurements. Elapsed time between the CTD and associated oxygen measurement is easily quantified, and corrected for, in post-processing. The black plenum and plumbing’s black tubing blocks light, reducing in-situ algal growth. Plumbing isolates the SBE 43 from continuous exposure to the external environment, allowing trapped water to go anoxic and minimizing electrolyte consumption between samples for moored deployments.


  • Voltage or frequency output.
  • Fully and individually calibrated; calibration drift rates of less than 0.5% over 1000 hours of operation (on time).
  • For use in CTD pumped flow path, optimizing correlation with CTD measurements.
  • Oxygen measurement dramatically improved because of improved temperature response.
  • Signal resolution increased by on-board temperature compensation.
  • Continuous polarization eliminates stabilization wait-time after power-up.
  • Hysteresis largely eliminated in upper ocean (1000 m) due to improved temperature response. Hysteresis at greater depths predicatable and correctable in post-processing.
  • No degradation of signal or calibration when used for profiling in hydrogen sulfide environments.
  • 600 or 7000 m housing.
  • Five-year limited warranty (during warranty period, one sensor re-charge [electrolyte refill, membrane replacement, recalibration] performed free of charge).

SBE 43 voltage output sensor integrated with SBE 19plus V2 CTD


  • SBE 43 voltage output sensor can be integrated with any Sea-Bird CTD that accepts 0-5 volt auxiliary sensor input (for example, SBE 9plus, 16, 16plus, 16plus-IM, 16plus V2, 16plus-IM V2, 19, 19plus, 19plus V2, 25, 25plus). It is available with 600 m plastic or 7000 m titanium housing; XSG or wet-pluggable MCBH connector; 0.5-mil membrane (fast response, typically for profiling applications) or 1-mil membrane (slower response but more rugged for enhanced long-term stability, typically for moored applications).
  • SBE 43F frequency output sensor can be integrated with SBE 52-MP or Glider Payload CTD, or used for OEM applications (requires OEM circuit board); it is available with 600 m plastic or 7000 m titanium housing. Another 43F version is used as an integral part in SBE 37-SIP-IDO MicroCATs.



Measurement Range 120% of surface saturation in all natural waters, fresh and salt
Initial Accuracy ± 2% of saturation
Typical Stability 0.5% per 1000 hours of deployed time (clean membrane)
Response time Tau * 2 to 5 sec for 0.5-mil membrane, 8 to 20 sec for 1.0-mil membrane
* Time to reach 63% of final value for a step change in oxygen;
dependent on ambient water temperature and flow rate (see Application Note 64 for discussion)


Input Power 6.5 - 24 VDC,
60 milliwatts (SBE 43) or 45 milliwatts (SBE 43F)
Output Signal 0 - 5 VDC (SBE 43), frequency (SBE 43F)


SBE 43 (voltage output) 600 m Plastic housing: 0.5 kg in air, 0.1 kg in water
7000 m Titanium housing: 0.7 kg in air, 0.4 kg in water
SBE 43F (frequency output) 600 m Plastic housing: 0.3 kg in air, 0.1 kg in water
7000 m Titanium housing: 0.4 kg in air, 0.2 kg in water



SBE 43 Voltage Output Sensor

SBE 43F Frequency Output Sensor (for 52-MP, Glider Payload CTD, and OEM applications)

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

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.

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.

Shown below are configuration selections for SBE 43 (top) and SBE 43F (bottom):

Family . Housing Connector Membrane Plenum
43 . 1 – 600 m (plastic) 1 – XSG 1 – 0.5 mil (profiling) 1
    2 – 7000 m (titanium) 2 – MCBH 2 – 1.0 mil (moored)  

Example: 43.1211 is an SBE 43 with 600 m housing, MCBH connector, and 0.5-mil membrane for profiling applications. See table below for description of each selection:

43 DISSOLVED OXYGEN SENSOR - Sea-Bird polarographic membrane sensor for pumped CTD applications, 0-5 volt temperature-compensated oxygen signal. Includes plenum & complete documentation. SBE 43 can be ordered in several ways:
  • By itself; consult Sea-Bird to order interface cable or mount kit separately, if needed.
  • As an option in SBE 9plus, 16plus V2, 16plus-IM V2, 19plus V2, or 25plus listing, complete with sensor, CTD interface cable, & mount kit.
For sensor with frequency output, compatible with SBE 52-MP Moored Profiler CTD or Glider Payload CTD, see SBE 43F below. Another version of 43F is an integral part of SBE 37 MicroCAT (SIP-IDO).
SBE 43 Housing Selections — MUST SELECT ONE
43.1xx1 600 m plastic housing

SBE 43 is available in plastic (600 m) or titanium (7000 m) housing.


43.2xx1 7000 m titanium housing
SBE 43 Connector Selections — MUST SELECT ONE
43.x1x1 XSG connector

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 shown; photo of MCBH connector not available

43.x2x1 Wet-pluggable (MCBH) connector
SBE 43 Membrane Selections — MUST SELECT ONE
43.xx11 0.5-mil membrane, Profiling configuration (fast response membrane, includes dynamic response characterization)

See Application Note 64 for information on response times for each membrane.

43.xx21 1.0-mil membrane, Mooring configuration (slower response rugged membrane for enhanced long term stability, dynamic response characterization omitted)
SBE 43 Spares & Accessories
171491 SBE 43 interface cable, AG/RMG connectors (9plus), 0.7 m (DN 32496) These interface cables are compatible with SBE 9plus, 19plus, 19plus V2, 25, or 25plus if connecting just SBE 43 to bulkhead connector. If connecting 2 sensors to 1 bulkhead connector, a Y-cable is required in place of one of these straight cables.

Note: 172447 and 172448 are also used for integrating SBE 43 with SBE 16plus, 16plus-IM, 16plus V2, or 16plus-IM V2. However, for moored applications, Sea-Bird usually recommends SBE 63 Optical Dissolved Oxygen Sensor instead of SBE 43.

172447 SBE 43 interface cable, AG/RMG connectors (19plus/19plus V2/25/25plus), 1.1 m (DN 32496)
172218 SBE 43 interface cable, Wet-pluggable connectors (9plus), 0.7 m (DN 32654)
172448 SBE 43 interface cable, Wet-pluggable connectors (19plus/19plus V2/25/25plus), 1.1 m (DN 32654)
801617 SBE 43 Plenum Assembly, Version 2, Black Acetal In 2007, Sea-Bird transitioned from using white plastic parts to black plastic parts for SBE 43, to minimize exposure to light, improving resistance to bio-fouling. Customers may retrofit existing SBE 43s.
50126 SBE 43 mount kit for SeaCATs For mounting SBE 43 to SBE 16, 16plus, 16plus-IM, 16plus V2, 16plus-IM V2, 19, 19plus, or 19plus V2 SeaCAT.
50109 SBE 43 mount kit for SBE 9plus  
50355 SBE 43 mount kit for SBE 25/25plus (hose clamp)  
90087 Universal plumbing kit (includes pump air release valve, Y-fitting, and tubing) — Application note 64-1 Application Note 64-1 details installation of plumbing for SBE 43 & pump on CTD.
30388 Tygon tubing, 1/2" ID x 3/4" OD, 2 m — main plumbing 30388 is main plumbing, attaches to pump, conductivity sensor, 1/2" nylon hose barb Y-fitting, etc. (photo shows 30388 tubing with SBE 9plus).
31450 Tygon tubing, 1/2" ID X 3/4" OD, 2 m, Black — main plumbing, minimizes light exposure 31450 can be used in place of 30388 plumbing tubing to minimize exposure to light, improving resistance to bio-fouling for moored applications. Sea-Bird uses this black tubing on all moored instruments (SBE 16plus/16plus V2 and 16plus-IM/16plus-IM V2 CTDs). Customers may field retrofit plumbing on existing systems.



Family Model . Housing Connector Membrane Plenum
43 F . 1 – 600 m (plastic) 1 – IE55 1 – 0.5 mil (profiling) 2 - Curved; for SBE 41, 41CP, 52MP
      2 – 7000 m (titanium)     3 - Flat; for Glider Payload CTD (GPCTD)

Example: 43F.1112 is an SBE 43F with 600 m housing, IE55 connector, 0.5-mil membrane for profiling applications, and curved plenum. See table below for description of each selection:

43F Dissolved Oxygen Sensor - Sea-Bird polarographic membrane sensor (fast response) for SBE Integrated CTD-DO profilers or OEM applications (Not compatible with SBE 9plus, 25/25plus, 19/19plus/19plusV2 or 16/16plus/16plusV2. Requires OEM circuit board - 41147). Temperature-compensated oxygen signal is a frequency output. IE55 3-pin connector. Includes plenum and complete documentation. (Order application specific interface cable separately - consult factory).

SBE 43F can be integrated with SBE 52-MP Moored Profiler CTD or Glider Payload CTD.

Another version of 43F is an integral part of SBE 37 MicroCAT (SIP-IDO).

For sensor with 0 - 5 volt output, compatible with most Sea-Bird CTDs, see SBE 43 above.

Shown with 7000 m titanium housing

SBE 43F Housing Selections — MUST SELECT ONE
43F.111x 600 m plastic housing  
43F.211x 7000 m titanium housing


SBE 43F DO Plenum Selections — MUST SELECT ONE
43F.x112 Plenum for use with SBE 41, 41CP, 52MP

Plenum for SBE 43F for use with SBE 41, 41CP, or 52-MP has a curved surface to allow for easy clamping to conductivity cell guard.

SBE 43F with curved plenum (43F.x112) SBE 43F with flat plenum (43F.x113) for integration with Glider Payload CTD
43F.x113 Plenum for use with Glider Payload CTD (GPCTD)



To SBE 9plus

  • 171491 To SBE 9plus (RMG/AG connectors), 0.76 m, DN 32496
  • 172218 To SBE 9plus (Wet-pluggable connectors), 0.76 m, DN 32654

To SBE 16plus, 16plus-IM, 16plus V2, 16plus-IM V2, 19plus, 19plus V2, 25, or 25plus

  • 172447 To CTD (RMG/AG connectors), 1.1 m, DN 32496
  • 172448 To CTD (Wet-pluggable connectors), 1.1 m, DN 32654

To Glider Payload CTD

  • 171558, 0.53 m, DN 32561

To SBE 52-MP

  • 171558, 0.53 m, DN 32561

Mount Kits

To SBE 9plus

  • 50109 SBE 5T, 43, or other 1.5-inch (3.81-cm) diameter housing instrument to 9plus Mount Kit

To SBE 16, 16plus, 16plus-IM, 16plus V2, 16plus-IM V2, 19, 19plus, or 19plus V2

  • 50126 SBE 5T, 5P, 5M, 43, or other 1.5-inch (3.81-cm) diameter housing to SBE 16/16plus/16plus-IM/16plus V2/16plus-IM V2, 19/19plus/19plus V2 or other 3.9-inch (9.9-cm) diameter housing Mount Kit

To SBE 25 or 25plus

  • 50355 SBE 25 Offset Block / Hose Clamp Kit for 5T, 5P, or 43
  • 50316 SBE 5T, 5P, or 43 to SBE 25 Cage Mount Kit

Spare Parts

  • 801617 SBE 43 Plenum Assembly, Version 2, Black Acetal
  • 31450 Tygon tubing, 1/2" ID X 3/4" OD, 2 meters, Black

Compare Oxygen Sensors

SBE Sensor Type Output Depth (m) User-
Can be
Integrated with
SBE 43 Dissolved Oxygen Sensor membrane 0 - 5 volts 600, 7000   Moored CTDs
(with 1.0-mil membrane),
Profiling CTDs
(with 0.5-mil membrane)
SBE 43F Dissolved Oxygen Sensor membrane frequency 600, 7000   Moored CTDs
(with 1.0-mil membrane),
profiling CTDs
(with 0.5-mil membrane)
SBE 63 Optical Dissolved Oxygen (DO) Sensor optical RS-232 600, 2000, 7000 Moored CTDs or slow profiling CTDs
** Products are no longer in production. Follow the links above to the product page to retrieve manuals and application notes for these older products.