Circuit arrangement for the compensation of temperature-dependent and temperature-independent drift and for the compensation of the sensitivity of a capacitive sensor

摘要

A circuits for compensating temperature-dependent and temperature- independent drift of a capacitive sensor including two measuring capacitors (3, 4) comprises pulse duration demodulators (11, 12) in the relevant input circuits. In accordance with pulses supplied by oscillators and whose duration is proportional to the capacitance of the capacitors, a d.c. voltage (U.sub.O) is applied to respective charging capacitors (17, 18) of the pulse duration demodulators (11, 12) for a predetermined period of time in order to charge this capacitors, after which zero potential is applied thereto in order to discharge the capacitors. The output of the relevant pulse duration demodulator is connected to the input (20, 21) of a summing/substraction member (19) whose output (23) supplies a d.c. voltage (U.sub.r). A d.c. voltage (U. sub.O), supplied by a controller (16) which compares one controller input d.c. voltage (U.sub.r) with a fixed reference voltage (U.sub.ref), is readjusted so that the d.c. voltage (U.sub.r) at the output (23) of the summing/subtraction member equals the fixed d.c. reference voltage (U.sub. ref) so that the output voltage (U.sub.a) of the circuit is free of temperature-dependent and temperature-independent drift.