GB761955A - Improvements in angular motion reproducing systems - Google Patents

Abstract

761,955. Electric control systems. GENERAL ELECTRIC CO. Nov. 25, 1954 [Nov. 25, 1953], No. 34220/54. Class 40 (1). In a positional control system using selsyns at transmitter T and receiver R, wherein the polyphase stators 6-8, 9-11 are energized from a polyphase supply and the error signal controlling the servomotor 15 to drive the receiver rotor 13, is derived from a phase comparison of the single phase outputs of the transmitter and receiver rotors 12, 13, the output of the transmitter is frequency divided for transmission at a lower frequency, and frequency multiplied at the receiver. As shown, the output of the transmitter rotor 12, the phase of which corresponds to its angular setting, is converted into pulse form at 23, e.g. by clipping, and frequency divided by four at 24, the resultant pulses modulating a carrier for transmission by line or radio at 17 to the receiver 21 where, after demodulation at 25, the pulses are frequency multiplied by four at 26 and converted into sinusoidal form for phase comparison at 22 with the output of the receiver stator 13. The system is independent of phase shifts introduced by the three-phase tie line 5 or by the signal transmission line, provided these phase shifts remain substantially constant, and for precision control the rotor 12 is driven by the control motion source 3 through a multiplying gear unit 14, the servomotor 15 driving the controlled apparatus 4 through reducing gearing 16, but driving the receiver rotor 13 directly. The invention is applicable to telemetering or control of an electrical power system, e.g. the control of a valve for a turbine. The signal transmission 17 may be effected over a telephone line.