Pressure measuring system with internal reference

摘要

A pressure measuring system which includes a pressure sensitive capacitor and a reference capacitor, a source of external excitation connected to the sensing capacitor, the reference capacitor being connected to a feedback signal generating circuit and the output from said capacitors being summed by a summing junction to produce an error signal. A phase sensitive demodulator is connected to receive the error signal and input same to a feedback signal generating circuit to generate the feedback signal for the reference capacitor. The feedback signal generating circuit includes a computing circuit for generating a digital signal corresponding to the magnitude of said feedback signal required to null said sensing capacitor signal to thereby provide a measurement of pressure. The system is characterized in that an excitation source for the systems phase sensitive demodulator is internally mounted closely proximate the sensing capacitor and the reference signal for the phase sensitive demodulator is derived directly from the input signal to the sensing capacitor to thereby obviate phase shift errors in the excitation thereof.