A CAPACITANCE DISPLACEMENT TRANSDUCER WITH LARGE DYNAMIC-RANGE, GOOD LINEARITY AND FREQUENCY READ-OUT

The design of a novel capacitance displacement transducer is described . A voltage-to-frequency converter is used as a voltage supply to a re sonant series LC circuit. The in-phase component of the voltage across the capacitor is detected using a phase-sensitive detector and the ou tput is fed back to the frequency-to-voltage converter so that resonan ce is maintained as the capacitance varies. The capacitance is then re ad out in terms of frequency by a computer. The system is simple, chea p and robust. We have achieved a dynamic range of three decades from 1 0 pF, frequency read-out resolution of 1 ppm and linearity of 0.2%.