Measuring pH in the deep ocean with Honeywell Durafet transistors

Measuring pH in the deep ocean presents challenges in sensor stability and accuracy. The Ion Specific Field Effect Transducer (ISFET) offers significant improvements over currently available technologies. The Honeywell Durafet is an ISFET that has a history of successful pH measurement in industrial processes. Principles of pH sensing with an ISFET will be presented including a discussion of adapting the Durafet for the ocean environment. Obtaining the accuracy desired for climate studies of pH requires a complete characterization of the sensor over the oceanographic temperature range and at pressures up to 2000 decibars. The calibration process will be described and field validation data presented.