Conco Inc.

Arnold W Feld

An induction motor is coupled to a three-phase AC source through thyristors controlled by a digital control circuit. An adjustable device gates a selected number of clock pulses to a control counter. As one of the AC phases goes positive, the control counter is incremented or decremented by clock pulses until reaching a predetermined count, which causes a trigger means to generate a trigger pulse and fire a thyristor. The trigger pulse also gates clock pulses to a second control counter which counts to 120.degree. and 240.degree. representing numbers in order to fire the other thyristors. In a speed feedback embodiment, rotation of the motor generates a motor feedback signal which is compared with a desired speed signal to adjust the count of an up/down counter, the contents of which are loaded into the control counter.

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Mendota, IL, United States of America

Arnold W Feld