Patent GB-657336-A (GB)
Title: Improvements in or relating to electric motor control systems
IPC: G05B11/01
Filed: 1948-12-01
Abstract: 657,336. Control of A.C. motors. WHEELCO INSTRUMENTS CO. Dec. 1, 1948, No. 31130. Convention date, June 1. [Class 38(iii)] [Also in Group XXXVIII] A control system for an electric motor having a control winding comprises circuit means connected to the control winding selectively to supply thereto alternating voltages of opposite phase, means to control the circuit means to determine the phase of the voltage supplied thereby to the control winding, a circuit connected to the control winding to supply a uni-directional voltage to the winding, switchmeans in the last-named circuit, and means responsive to the flow of current in the circuit means to control the switch means. A pointer 11 is moved by a sensitive instrument 10 in response to changes in a condition which is to be recorded or controlled and carries a metal flag 12 movable between inductance coils 13 which are supported on lever 14 pivoted concentrically with the pointer. The coils 13 are adapted to vary the tuning of an oscillator comprising discharge valve 15 the anode circuit of which includes tuned circuit 16, 17, supply-source 18, load resistor 19, and an additional supply-source 22. When the flag 12 occupies a position substantially half-way into the coils, the oscillator is so tuned that the current passing through resistor 19 biasses an amplifier valve 23 in such manner that valves 36, 37, are rendered non-conductive. No current is then supplied to the control winding 38 of a two-phase induction motor which remains stationary. If the flag is moved into the coils the anode current of the valve 15 is increased, that of the valve 23 is decreased, the valve 36 passes current, and the valve 37 is cut off. The upper section 33 of a transformer primary winding is energized, the motor control winding 38 being so excited through the transformer secondary winding 32 that the lever 14 moves away from the pointer 11 to re-establish the neutral relationship between pointer and lever. Upon movement of the flag away from the coils. the valve 37 is rendered conductive to energize the section 34 of the transformer primary winding, so producing a control voltage of opposite phase for the control winding 38 of the motor which runs in the opposite direction. If current flows through either of the winding sections 33, 34, a voltage is developed across a resistor 46 so providing a grid bias component, opposing that from a potentiometer 48, for a gas-filled valve 45. The valve is thereby cut off, the only current supplied to the control winding 38 being that from the transformer. As scon as current stops flowing through the transformer primary winding, the voltage across resistor 46 is removed and directcurrent is supplied to the motor control winding through the valve 45, so producing a rapid braking-effect.' In a modification (Fig. 2, not shown), the motor is controlled by means of a resistance bridge comprising a resistor variable in response to changes of a condition to be recorded or regulated, and a resistor connected to the reversible motor to be varied thereby. The motor may drive a pen carriage 42.