Admittance measuring system for monitoring the condition of materials
US3993947A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Sep 19, 1974 |
| Grant date | Nov 23, 1976 |
| Priority date | — |
| Expiry date | Sep 19, 1994 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG01N27/028
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
An intrinsically safe system for monitoring the condition of materials includes a low power, stable frequency RF oscillator of the class C type comprising a resonant circuit which is coupled to a bridge network including the admittance of materials between a probe electrode and a grounded support member juxtaposed to the materials. The output of the network generates an AC error signal which is applied to a phase sensitive detector including a chopper and a low power chopper drive for generating a DC signal representing the magnitude of the AC signal at a predetermined phase angle. The bridge network which may be linearly calibrated is isolated from the oscillator and the output error signal circuitry so as to allow the oscillator and the output error signal circuitry to float with respect to the grounded support member and the power supply associated therewith. The rms voltage across the admittance representing the condition of materials is limited so as to permit the system to comprise a two-wire transmitter wherein the sole source of power for the transmitter is derived from a 4-20 milliamp current drawn by the transmitter.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.