Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Patent
1996-09-26
1998-05-26
Karlsen, Ernest F.
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
324681, 307116, 340562, 361181, G01R 2726, H03K 17955
Patent
active
057571961
ABSTRACT:
A capacitive proximity or limit switch comprises a capacitive probe having a sensor electrode and a guard electrode. The sensor electrode is connected to an oscillator formed by a feedback system of two operational amplifiers, of which one operational amplifier is configured as a differential amplifier, the other operational amplifier as a voltage follower. The probe electrode is connected to the inverting input of the differential amplifier, in the feedback circuit of which a capacitor is provided, as a result of which the AC gain is determined. An adjustable portion of the output voltage of the differential amplifier is applied to the non-inverting input of the voltage follower, the output of which is connected to the non-inverting input of the differential amplifier to which the guard electrode is connected. As a result of this, the start and stop of oscillation of the oscillator is determined by variations of the capacitance of the sensor electrode, and the guard electrode is always maintained precisely at the same AC potential as the sensor electrode.
REFERENCES:
patent: 3743865 (1973-07-01), Riechmann
patent: 3764819 (1973-10-01), Muller
patent: 3870948 (1975-03-01), Holt et al.
patent: 4219740 (1980-08-01), Little
patent: 4879474 (1989-11-01), LaMarche
patent: 5367198 (1994-11-01), Buergel et al.
Do Diep
Endress & Hauser GmbH & Co.
Karlsen Ernest F.
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