Waveform crossing detector

Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Phase comparison

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Details

323325, 324 83R, 361 76, G01R 2500

Patent

active

044954611

ABSTRACT:
A waveform crossing detector circuit for a pair of waveforms of a three-phase AC supply applied to respective input terminals (7,8,9). The circuit includes a pair of opto-couplers (1,3; 2,4) for isolating an output terminal (21) from the supply. In order to obtain an accurate indication of the instants of crossing the light-emitting diodes (1,2) of the couplers are driven by respective transistors (5,6) which act as the actual crossing detectors. The collector circuits of these transistors are driven from the third phase, the potential of which is at a maximum when the relevant instants occur. Two further such arrangements may be connected to the taps (22,23,24) of an input potential divider in a cyclical manner and the output signals of the three resulting arrangements combined by means of logic gates to produce pulses which occur once every 60.degree. of the input waveform. The output signal may be used as a reference signal to enable control signals for thyristors included in a control circuit for apparatus energized from the AC supply.

REFERENCES:
patent: 3332008 (1967-07-01), Mueller et al.
patent: 3436645 (1969-04-01), Johnson et al.
patent: 3659196 (1972-04-01), Bercovitz, Jr.
patent: 3746969 (1973-07-01), Gessaroli et al.
patent: 3780318 (1973-12-01), Werts et al.
patent: 3854089 (1974-12-01), Emler
patent: 4024439 (1977-05-01), McClain et al.
patent: 4119905 (1978-10-01), Head
patent: 4176288 (1979-11-01), Komatsu et al.
G. Oliver et al., "Optoisolators Slash Cost of Three-Phase Detector", in Electronics, Nov. 23, 1978, p. 146.

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