Capacitance measuring by comparison to reference capacitance

Details Capacitance measuring by comparison to reference capacitance Capacitance measuring by comparison to reference capacitance

1978-09-25

1980-02-05

Mullins, James B.

Electricity: measuring and testing

Conductor identification or location

Inaccessible

324 60C, G01R 2726

Patent

active

041874609

ABSTRACT:
Capacitance measuring device for measuring a physical quantity proportional or inversely proportional to the capacitance X of a first capacitor. A oscillating circuit includes a second capacitor having a reference capacitance X.sub.E or the first capacitor during successive reference and measuring phases under control switching network respectively. A counter counts a predetermined oscillation pulse number N.sub.E during the reference phase and a oscillation pulse number N.sub.X during the measuring phase. The duration of two phases are equal or in a predetermined ratio R by means of a counter-down-counter which counts and down-counts the same number of clock pulses at least a predetermined frequency. The change of the counting to down-counting condition is controlled by the counter when its count is equal to N.sub.E. The stopping of the counter is controlled by the counter-down-counter when its count is equal to zero at the end of the measuring phase. A displaying and computing unit computes the physical quantity in dependence on the capacitance value X=(N.sub.E X.sub.E)/(R N.sub.X) which is not affected by the drifts of device components and interference capacitances.

REFERENCES:
patent: 3824459 (1974-07-01), Uchida
patent: 4039940 (1977-08-01), Butler et al.

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