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SBE-43 Dissolved Oxygen

SBE-43 Dissolved Oxygen
The SBE 43 sets the oxygen measurement standard for oceanographic research. The sensor is a complete redesign of the Clark polarographic membrane type in which careful choices of materials, geometry, and sensor chemistry are combined with superior electronics interfacing and calibration methodology to yield major gains in performance.

SBE-43 Dissolved Oxygen

Sea-Bird Electronics

The SBE 43 sets the oxygen measurement standard for oceanographic research. The sensor is a complete redesign of the Clark polarographic membrane type in which careful choices of materials, geometry, and sensor chemistry are combined with superior electronics interfacing and calibration methodology to yield major gains in performance.

Calibration stability is improved by an order of magnitude, and the sensor requires less frequent calibration. Calibration drift is caused primarily by membrane fouling from ocean contaminants, and less so by chemical processes inside the sensor. If the membrane is kept clean, the sensor’s improved chemical stability yields demonstrated calibration drift rates of less than 0.5% over 1000 hours of operation (on time).

Temperature response is dramatically improved. The chemical and physical processes that underlay the oxygen measurement are very sensitive to temperature. Accurate characterization of the internal sensor temperatures that control these processes, especially when water temperature is changing rapidly, is a key accomplishment of this design. Not only does the SBE 43 sensor measure temperature in the right place: the temperature equilibration time of the entire sensor head has been reduced to a few seconds, so it tracks the changing water temperature much more faithfully.

Hysteresis is largely eliminated in the upper ocean (1000 meters) due to improved temperature response. Residual mismatch between up and down casts in this part of the ocean is due to sensor alignment, correctable in post-processing. At higher pressures, changes occur in gas-permeable Teflon membranes that affect their permeability characteristics. These changes have long time constants, depend on the sensor's time-pressure history, and result in hysteresis at depths greater than 1000 meters. These effects are predictable and are also correctable in post-processing. The resultant SBE 43 measurement resolves oxygen features more precisely, reducing the ambiguity about locking measured sensor values to bottle Winklers.

Continuous polarization eliminates stabilization wait-time after power-up. The sensor is always ready for immediate use. Earlier sensors required several minutes to polarize following power-up. During that time, sensor readings were inaccurate. In the SBE 43, micropower electronics and an internal, five-year, board-mounted battery eliminate power-up delay.

Poisoning in hydrogen sulfide environments was a phenomenon common to early oxygen sensor designs that used silver as the cathode element. The SBE 43 uses a noble metal (gold) as the cathode and silver as the anode, and shows no degradation of signal or calibration when used for profiling in hydrogen sulfide environments.

Signal resolution is increased by on-board temperature compensation, and a CTD channel is made available for other purposes because there is no temperature output signal. Even when oxygen concentration is constant, the normal range of ocean temperatures causes the output of earlier sensors to vary by a factor of two. The SBE 43’s internal temperature compensation eliminates this variation, allowing the sensor to pre-amplify the signal proportionately; resolution with existing CTD systems is correspondingly increased.

Effective plumbing strategies allow for longer moored deployments. Plumbing isolates the SBE 43 from continuous exposure to the external environment, allowing trapped water to go anoxic, minimizing electrolyte consumption between samples. The black plenum and installing black tubing block light, reducing in-situ algal growth.

Documents

Brochure
SBE-43 Brochure - Download

Application Note
AN 64: SBE 43 Dissolved Oxygen Sensor -- Background Information, Deployment Recommendations, and Cleaning and Storage - Download
AN 64-1: Plumbing Installation -- SBE 43 DO Sensor and Pump on a CTD - Download
AN 64-2: SBE 43 Dissolved Oxygen Sensor Calibration and Data Corrections - Download
AN 64-3: SBE 43 Dissolved Oxygen (DO) Sensor -- Hysteresis Corrections - Download
AN 71: Desiccant Use and Regeneration (drying) - Download


References

Technical Papers
Murphy et al., 2008. Improvements to the SBE 43 Oxygen Calibration Algorithm. - Download

Jenzen et al., 2007. Getting More Mileage out of Dissolved Oxygen Sensors in Long-Term Moored Applications. - Download