EFFECTS OF PRESSURE ON OXYGEN SENSORS

To measure the effects of pressure on the output of a membrane oxygen sensor and a nonmembrane oxygen sensor, the authors pressure cycled a CTD sensor package in a laboratory pressure facility. The CTD sensor p ackage was cycled from 30 to 6800 db over a range of temperatures from 2 degrees to 38 degrees C. Pressure decreased the output of the membr ane sensor and increased the output of the microhole sensor. The press ure terms for both types of oxygen sensors were affected by temperatur e. The effect of pressure on both types of sensors can be quantified a s exp(VP/R'T), where V is a coefficient (cm(3) mol(-1)), P is decibars , R' is the gas constant (831.47 cm(3) mol(-1) db K-1), and T is kelvi ns. As water gets colder, V for both sensors increases. For temperatur es less than 21 degrees C, V for the membrane sensor is -33.7 +/- 0.54 cm(3) mol(-1), and V for the microhole sensor is 0.29 +/- 0.31 cm(3) mol(-1). The V's for calibrations of four oceanic casts had larger ran ges than the laboratory experimental data: -27.6 to -34.9 cm(3) mel(-1 ) for the membrane sensor, and -0.4 to -2.9 cm(3) mel(-1) for the micr ohole sensor. At 10 degrees C, increasing pressure to depths of 5000 m decreases current output of a membrane sensor approximately 50% and i ncreases output of a microhole sensor about 0.6%. For field calibratio ns, the authors recommend using a constant V obtained by iterations of linear fits. The use of a pressure term with the form exp (VP/R'T) ap pears to improve field calibrations of membrane oxygen sensors.