Patent ID: 8253426
Filing Date: 2012-08-28
Classification: G01D,G01P,G11B

Abstract:
1. A capacitance detector for outputting an electric signal dependent on a capacitance present on an object to be measured, the capacitance detector comprising: a measurement terminal to be disposed in contact with or in proximity to the object being measured; an impedance conversion circuit connected to the measurement terminal to form a resonant circuit; a reference phase oscillator for supplying a reference phase signal at a constant frequency to the resonant circuit; phase comparison means for outputting, as a capacitance detected signal, a phase difference signal indicative of a phase difference between a resonant signal, which is extracted from the resonant circuit in response to the reference phase signal being applied to the resonant circuit, and the reference phase signal; and resonance frequency regulation means for regulating the resonance frequency of the resonant circuit based on the phase difference signal, wherein: the resonance frequency regulation means includes a signal operational unit for outputting, as an error signal, a difference between a signal level of the phase difference signal and a target value of the signal level of the phase difference signal, and a controller for integrating the error signal for output as a control signal; and a circuit constant of the resonant circuit is determined based on the control signal.