Evaluation unit of a differential-pressure sensor

An evaluation unit of a differential-pressure sensor having

• a sensor element (1) with
• a liquid-filled measuring chamber (11),
• a first diaphragm (3a) to which a first process pressure (P.sub.x) which acts on the sensor element (1) is applied, the first process pressure corresponds to the sum of a static pressure (P.sub.S) and a first pressure (P.sub.1),
• a second diaphragm (3b) to which a second process pressure (P.sub.y) which acts on the sensor element (1) is applied, the second process pressure corresponds to the sum of the static pressure (P.sub.S) and a second pressure (P.sub.2), and
• two measuring capacitors (4, 5) whose capacitances (C.sub.1, C.sub.2) change in the opposite direction to the difference between the first and second pressures and in the same direction as the static pressure (P.sub.S),
• a temperature sensor (6) which is arranged on the sensor element (1) and
• a temperature measuring circuit (7) which is connected to the temperature sensor (6) and which supplies an output signal which corresponds to the sensor temperature (T.sub.S), which evaluation unit comprises:
• a measuring circuit (8) for determining the respective reciprocal values (1/C.sub.1, 1/C.sub.2) of the capacitances of the measuring capacitors (4, 5) and
• an arithmetic unit 9
• which determines the sum (.SIGMA.) of the reciprocal values (1/C.sub.1, 1/C.sub.2) of the two capacitances,
• which determines the difference (.DELTA.) between the reciprocal values (1/C.sub.1, 1/C.sub.2) of the two capacitances and assigns a differential-pressure measured value (.DELTA.P.sub.M) to said difference, and
• which outputs an output signal which corresponds to a differential pressure (.DELTA.P), specifically to the difference (P.sub.1 -P.sub.2) between the first and second pressures, and wherein
• an internal temperature (T.sub.i) is assigned to the sum of the reciprocal values of the capacitances (.SIGMA.),
• the internal temperature (T.sub.i) being equal, with the exception of a temperature discrepancy (T.sub.0), to the sensor temperature (T.sub.S) when
• there is no static pressure (P.sub.S) applied to the two diaphragms (3a, 3b) and the difference between the first and second pressures is equal to zero,
• a first correction value (.DELTA.K) is determined in accordance with
• .DELTA.K=T.sub.i -T.sub.S -T.sub.0,
• which is a measure of the static pressure (P.sub.S) at a reference temperature (T.sub.R),
• (T.sub.0) being the temperature discrepancy (T.sub.0), determined at the reference temperature (T.sub.R), between the sensor temperature (T.sub.S) and the internal temperature (T.sub.i), and
• a differential pressure (.DELTA.P) which has been corrected with respect to a measuring error due to the static pressure (P.sub.S) is determined from the differential-pressure measured value (.DELTA.P.sub.M) using the first correction value (.DELTA.K).