A capacitance displacement transducer with large dynamic range, good linearity and frequency read-out

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Abstract
The design of a novel capacitance displacement transducer is described. A voltage-to-frequency converter is used as a voltage supply to a resonant series LC circuit. The in-phase component of the voltage across the capacitor is detected using a phase-sensitive detector and the output is fed back to the frequency-to-voltage converter so that resonance is maintained as the capacitance varies. The capacitance is then read out in terms of frequency by a computer. The system is simple, cheap and robust. We have achieved a dynamic range of three decades from 10 pF, frequency read-out resolution of 1 ppm and linearity of 0.2%.

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