Capacitance measuring by comparison to reference capacitance
US4187460A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Sep 25, 1978 |
| Grant date | Feb 5, 1980 |
| Priority date | — |
| Expiry date | Sep 25, 1998 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG01R19/252
- WIPO fieldMeasurement
- WIPO sectorInstruments
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.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.