Performance of the low pressure differential and absolute digiquartz pressure transducers

Long term performance of pressure transducers used for sea level measurements was assessed. The differential and low pressure absolute digiquartz instruments exhibit extremely good long term stability but suffer from short term instability which leads to initial drift and is caused by the mechanics of the bellows. Differences in calibrations over several years can mostly be accounted for in terms of common mode line pressure effects, whereas changes in the zero pressure output are a result of the mechanical instability of the bellows. The exponential drift that can occur is shown to be reversible and has a time constant of 40 hr. Thus, datum shifts occur when the transducer is deployed, the magnitude of which depends on the particular transducer and the differential pressure.