GB877772A - Control current circuit for magnetic amplifiers - Google Patents

Abstract

877,772. Control of A.C. motors. LANDIS & GYR A.G. April 15, 1959 [April 24, 1958], No. 12811/59. Class 38 (3). [Also in Group XXXIX] In a correspondence control system comprising an adjustable transmitter potentiometer 21, and a follower potentiometer 23 driven by a reversible control motor 22 through gearing 36, the control loop includes two auto-self-excited full-wave rectifying transductors 8, 9 which are supplied from a common centre-tapped tran-s former 4 and energize respective opposed coils 10, 11 of a centre-stable relay 15, the direction of error current supplied by the potentiometers to the control windings 20 determining the direction of operation of the relay and the consequential direction of rotation of the motor. A bias winding 16 and an external feedback winding 25 is provided for each transductor, and the degree of feedback may be such as to provide stable high and low current operating states. The relay 15 selectively operates a switching relay 34 or 35 which completes a directional current path to the motor and inserts resistance 27 in the control winding circuit. Paralleled rectifiers 24 limit the control current. Due to the insertion of resistance 27 by the operated switching relay, the control winding current is sufficiently reduced as to establish a low current output from the operative transductor when correspondence between the potentiometers 21, 23 is approached, and interaction then takes place between the transductor, relay 12 and the relevant switching relay whereby the transductor is alternately brought into the high and low output current states. As a result the motor is slowed down and hunting avoided.