Capacitive measuring device for determining displacement by eval

Details Capacitive measuring device for determining displacement by eval Capacitive measuring device for determining displacement by eval

1994-04-22

1995-10-24

Wieder, Kenneth A.

Electricity: measuring and testing

Impedance, admittance or other quantities representative of...

Lumped type parameters

324660, 324681, 34087037, G01R 2726, G08C 1910

Patent

active

054613205

ABSTRACT:
A capacitive measuring device or apparatus; in particular, a length-measuring apparatus, which incorporates a scale portion and a scanning unit which is movable relative to the former and which supports transmitting electrodes and at least one receiving electrode. Herein, a transmission circuit applies transmitting signals at a basic frequency to the transmitting electrodes, and with the receiving electrode being connected to a reception circuit, to the output side of which there is connected an evaluating circuit for the receiving signals. The transmitting signals are applied to the transmitting electrodes through a pulse width modulator and a synchronous modulator and the receiving signal is conducted through a demodulator. The synchronous modulator and demodulator operate at the same modulation frequency, which is higher than the basic or basic frequency; and when the scanning unit is at a standstill relative to the scale portion, the base frequency of the receiving signal is equal to the base frequency of the transmitting signals, and upon movement of the scanning unit relative to the scale portion the basic frequency of the receiving signals changes in conformance with the speed of movement relative to the basic frequency of the transmitting signals, whereby a change in frequency is evaluated by the evaluating circuit so as to display the length or extent of the movement.

REFERENCES:
patent: 4743902 (1988-05-01), Andermo
patent: 5053715 (1991-10-01), Andermo
patent: 5065105 (1991-11-01), Bruere et al.
patent: 5122755 (1992-06-01), Nootbaar et al.

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