Equipment for compensating for sensor variations

Abstract

The output of the sensor whose variations are to be compensated is applied to one input of a DC amplifier whose other input is connected to an analog storage. The output of the DC amplifier is applied to a voltage-controlled oscillator whose frequency varies as a function of the voltage applied thereto. A phase detector compares the output of the voltage controlled oscillator to a standard reference frequency and furnishes a DC compensating voltage corresponding to the difference therebetween. Prior to each measurement the DC compensating voltage is applied to the analog storage thereby forming a closed loop circuit and causing the voltage controlled oscillator to oscillate at its standard frequency. At the start of the measurement the connection between the phase detector and the analog storage is broken thereby causing the DC compensating voltage present at the beginning of the measurement to be applied to the DC amplifier throughout the measurement. The frequency of the output of the voltage controlled oscillator then varies as a function of the sensed signal and is counted by a counter controlled by timing signals derived from the oscillator furnishing the standard frequency signal to the phase detector.