Method of detecting a variation in stray capacitance by use of a

Details Method of detecting a variation in stray capacitance by use of a Method of detecting a variation in stray capacitance by use of a

1992-07-13

1993-09-14

Wieder, Kenneth A.

Electricity: measuring and testing

Impedance, admittance or other quantities representative of...

Lumped type parameters

324681, 324682, 324674, 324675, 324661, 324606, 331 65, G01F 2326

Patent

active

052452956

ABSTRACT:
Disclosed is a method of detecting a variation in stray capacitance by use of a PLL circuit. This method involves the steps of: setting respectively a freerunning frequency and a capture range of a phase-locked loop circuit so that a range in which an output frequency of a pre-oscillator changes extends to an interior of the capture range of the phase-locked loop circuit, the output frequency being determined by a synthetic time constant obtained by adding up a variation value of an electric capacitance or the like that is detected by a sensor and a reserve time constant preset in a time constant determining module when detecting the stray capacitance by employing the sensor for detecting the variation in the stray capacitance in contact or non-contact with a body to be detected and a capacitance detecting means including the pre-oscillator having the time constant determining module connected to the sensor and the phase-locked loop circuit connected to the pre-oscillator; detecting a change in a freerunning frequency control voltage in a locked state of the phase-locked loop circuit, the change being caused with the variation in the electric capacitance or the like that is detected by the sensor; and detecting a state variation of the detected body.

REFERENCES:
patent: 4169260 (1979-09-01), Bayer
patent: 4173736 (1979-11-01), Adams
patent: 4228393 (1980-10-01), Pile
patent: 4347740 (1982-09-01), Townsend
patent: 4347741 (1982-09-01), Geiger
patent: 4972566 (1990-11-01), Andersen
patent: 5034722 (1991-07-01), Premack

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