Processing module for a capacitive pressure sensor

摘要

The sensor (1) consists of a liquid filled measurement cell with membranes (3a, 3b) each subject to a static pressure (Ps) plus an additional pressure (P1, P2). The capacitances of measurement capacitors (C1, C2) change with changes in pressure. A temperature measurement circuit (7) converts the output of a temperature sensor (6) to a signal corresponding to the differential pressure sensor temperature. A measurement circuit (8) retunes the inverse values (1/C1, 1/C2) and a computer (9) determines the sum ( ) of the inverse capacitances and from their difference ( DELTA ) a differential pressure value ( DELTA Pm) providing an output signal which corresponds to the difference (P1-P2). The sum of the inverse capacitances (1/C1, 1/C2) relates to an internal temperature (Ti) which is equal to a temperature off-set (T0) when neither membrane is subjected to a static pressure, and no differences exists between the first and second pressures and a first correction value ( DELTA K) is determined from the relationship: DELTA K = Ti-Ts-T0 where the correction value at a temperature (Tr) is a measure of the static pressure (Ps). The differential pressure is then determined from the differential pressure value ( DELTA Pm) by applying the correction value ( DELTA K) to allow for the static pressure.