Capacitance measuring apparatus with means for nulling the resis

Details Capacitance measuring apparatus with means for nulling the resis Capacitance measuring apparatus with means for nulling the resis

1988-05-31

1991-05-07

Eisenzopf, Reinhard J.

Electricity: measuring and testing

Impedance, admittance or other quantities representative of...

Lumped type parameters

324658, G01R 2726

Patent

active

050140116

ABSTRACT:
A circuit and method for measuring the capacitance of a medium independent of the resistivity of the medium. A triangular voltage is applied to plates immersed in the medium to generate both a resistive current component in phase with the triangular voltage and a capacitive current component in phase with a differential of the triangular voltage. The resistive and capacitive current components are summed with a selectable current which is provided having a phase .pi. radians out of phase with the triangular voltage and having an amplitude related to a control signal. The summed current is sampled over a time period phase shifted from the capacitive current component and then integrated so that the capacitive current component integrates to zero and the integral of the resistive current component minus the selectable current provides the control signal. In response to the control signal, the selectable current is varied until the sum of the selectable current and resistive current component are nulled. This summed current is then sampled in phase with the capacitive current component thereby obtaining a measurment of capacitance independent of resistance.

REFERENCES:
patent: 3486108 (1969-12-01), Rosica et al.
patent: 3947760 (1976-03-01), Noguchi et al.
patent: 4288741 (1981-09-01), Dechene et al.
IEEE Transactions on Vehicular Technology, vol. VT-27, No. 3, Aug. 1978, p. 142, "An On-Board Sensor For Percent Alcohol", Hille et al.

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