Capacitance measurement via discharge current arithmetic mean determn., esp. for level sensing capacitive transducer

摘要

The measurement method involves switching (S2) a capacitance (CM) to be measured periodically to a predetermined reference voltage (U) for charging, and is discharged via a further switch (S3) into an evaluation unit (15) contg. a switched ohmic resistance (S1,23). The input terminals (16,17) of the evaluation unit are connected to the output terminals (30,31) through a low-pass filter (25,27) nullifying the effect of stray capacitances. No switching takes place during the discharge phase, when the arithmetic mean of the output voltage is taken.