Patent GB-827729-A (GB)
Title: Improvements in signalling systems for controlling remote apparatus
IPC: G08C19/22
Filed: 1956-02-24
Abstract: 827,729. Electric correspondence control. ELECTRICITE DE FRANCE. Feb. 24, 1956 [Feb. 26, 1955], No. 5903/56. Class 40 (1). [Also in Group XXXV] A signalling system for controlling remote apparatus in dependence upon the magnitude of a control voltage, comprises means for generating a comparison voltage having a substantially constant rate of change of amplitude and commencing at a predetermined datum level, an electric discharge valve, means for applying the comparison voltage and the control voltage to the electric discharge valve in such a manner as to cause a change in the state of conduction of the valve when the comparison voltage reaches a value fixedly related to the magnitude of the control voltage, means responsive to said change of state to cause the comparison voltage to return to said datum level and a control relay responsive to said change of state to control the operation of remote apparatus. As shown, the control voltage is produced by a device 1 and is D.C. either positive or negative, its amplitude varying in accordance with changes in frequency of an electric power system. The relay (RE1 or RE2) is used to control a constant speed electric motor M which operates the control valve of a turbo-electric generator supplying the system, to regulate its frequency. The device 1 is connected to the control grids and cathodes of two thyratron discharge valves LI, L2; the connections are arranged so that the control grid of one thyratron is driven positive and the control grid of the other negative with respect to their cathodes. The anode circuits of the thyratrons are supplied from separate D.C. high-tension sources through the contacts d1<SP>1</SP>, d2<SP>1</SP> of a relay RE3. The relay RE3 is controlled by contacts 3, 4 which are closed by a cam 2 driven by a synchronous motor MS. When the relay RE3 is unoperated high tension is applied to both thyratrons and the one which has its grid driven positive by the voltage from the device 1 (L2, for example) immediately fires and closes the relay (RE2 in the case of thyratron L2) in its anode circuit. The relay through its contacts c2 closes a supply circuit to the motor M which then commences to operate. The other thyratron (L1) is held inoperative by the negative voltage on its control grid but a condenser C1 which is connected so as to offset this voltage commences to charge from the hightension line through a resistance R1 and after a time, the duration of which depends upon the amplitude of the voltage supplied by the device 1, the condenser charges sufficiently so that the thyratron L1 can fire. The relay RE1 in its anode circuit is then operated and through its contacts b1 stops the motor M. If the voltage supplied by the device 1 had been of the opposite plurality the thyratron L1 would have fired first and the motor M would then have been rotated in the opposite direction through the contacts c1 of the relay RE1 and this rotation would have been terminated by the contacts C2 of the relay RE2. The thyratrons are biased so that in the event of the device 1 producing no output voltage both of them fire simultaneously immediately the relay RE3 operates and since both relays RE1 and RE2 operate, the motor M receives no supply and does not operate. The cycle is terminated by the synchronous motor making the contacts 3, 4 and cutting off the supplies to the anodes of the thyratrons. The operation of relay RE3 also discharges the timing condensers C1 for thyratron L1 and C2 for thyratron L2 through resistances R9, R10 and contacts e1, e2. The sequence commences again when the contacts 3, 4 are broken by the operation of the synchronous motor. The circuit shown is provided with two optional features, the first of these prevents the thyratrons producing impulses which are too short to operate the motor M. This is accomplished by providing the relay RE3 with contacts #1, #2, and the arrangement is such that when the relay is operated these contacts are connected to the high-tension supplies and when the relay is released they remain connected for a short time after the contacts d1<SP>1</SP>, d2<SP>1</SP> are connected to the high-tension supplies; the contacts #1, #2 are connected to potential dividers and when they are connected to the high-tension supplies the control grids of the thyratrons are at a positive potential; thus for a short time immediately after the relay RE3 releases, the anodes and control grids of both thyratrons are connected to positive potentials and the potentials on the control grids are arranged to be sufficient to offset any negative potential from the device 1 unless this negative potential is sufficient to produce an impulse of sufficient duration to operate the motor M; if the negative potential is insufficient then both thyratrons fire and the motor remains inoperative. The second feature prevents the motor M being continuously operated which could otherwise happen with a sufficient amplitude of signal from the device 1. This is accomplished by providing contacts 30, 40 which are operated by a second cam 20 controlled by the synchronous motor MS. At a desired point towards the end of the cycle these contacts are made and if neither of the relays RE1, RE2 has operated a relay RE4 is operated to stop the motor M. If one or other of the relays RE1, RE2 has operated then contacts on the relays prevent operation of the relay RE4 by short-circuiting its operating coil. This shortcircuiting can be prevented if desired by means of a manually operable push-button 23. When the relay RE4 is operated an alarm 24 is energized.