Dynamic Response of CTD Pressure Sensors to Temperature

Abstract

Pressure sensors used in CTDs (conductivity temperature depth) respond to transients in temperature. It is often assumed that these transients have a negligible effect on pressure. However, in a Sea-Bird CTD used in Hawaiian waters, these transients lead to pressure errors as high as 8 db. We describe how we correct these errors using linear system theory by computing the response function of the pressure sensor to temperature transients. The CTD housing insulates the pressure sensor from the water to some extent, so that the effective response function is a combination of the intrinsic response of the pressure transducer convolved with a response function due to transfer of heat through the housing. Using this method, pressure is corrected to within 1 db. The impulse response functions for two similar pressure tranducers are quite different, probably due to small manufacturing variations. Thermal insulation of pressure sensors also varies from CTD to CTD. The net effect is that the response functions vary considerably from CTD to CTD.