Patent GB-518620-A (GB)
Title: Improvements relating to electrical remote-control or signalling systems
IPC: H02J13/00
Filed: 1938-08-26
Abstract: 518,620. Selective signalling over power circuits. SANGAMO WESTON, Ltd., GILLIVER, G., and TAGG, G. F. Aug. 26, 1938, Nos. 25132, 27087, 29240, and 32422. [Class 40 (i)] A direct current impulse for signalling is applied to an A.C. power circuit by connecting a battery in series with a choke or a rectifier in series with a resistance between the mains and inserting a resistance in one of the mains between the point of connection and the A.C. source. Transmitting apparatus. As shown in Fig. 1, operation of one of the switches 9, 10 by hand or under clock control energizes the corresponding switch 11, 12 to connect battery 3 in one or other direction in series with choke 13 between the neutral wire and phase 1 and to cause switch 15 to remove a shunt from resistance 14 in the neutral wire. The receiving stations, some of which are designed to respond 'to single signals of any length and some only if the duration of a single signal exceeds a predetermined length, respond only to a signal of the opposite polarity to that of the immediately preceding signal. Other receiving stations respond to a characteristic number of signals regardless of their polarity. To control these the operator sets a radial switch 76 to the appropriate position and momentarily operates switch 75 to start a motor 71 driving a series of cams which operate pairs of contacts such as 68<1>, 69<1> in succession. An off-normal cam keeps the motor running until the cam shaft has made a complete revolution. Each time one of the springs 68<1>, 68<2> &c. is operated a circuit is made for 79 which energizes 11 or 12 to send an impulse to line. The polarity of the impulse is determined by the condition of a ratchet relay 81, and is always the same as that of the signal most recently sent to the single impulse stations. When the impulse corresponding to the position of switch 76 is sent the corresponding lower spring energizes a ratchet relay 67 which renders further impulses from the machine ineffective. At the end of the cam shaft cycle, 67 receives a further impulse to restore it to the condition shown. In a modified sending circuit, Fig. 5 (not shown), the switches 5, 6 connect a one-way rectifier in series with a resistance instead of a battery and choke between the neutral wire and a phase wire. Tell-tale indicators at transmitter. Relays 46 ... 48 polarized by rectifiers 50, 51 respond to the single impulses on the line and if the duration of one kind of signal is sufficient, thermal relay 59 closes its contacts. As a consequence magnet 52, 53 or 54 is energized and indicator member 55 moves to the corresponding position. Relay 121 repeats the stream of impulses to the driving magnet 119 of a stepby-step switch which controls the resistance in circuit with a current meter 123. The circuit of the latter is completed when the transmission of impulses has been completed and is maintained by relay 126, which locks over an offnormal bank until the next operation of key 75, whereupon the step-by-step switch goes home. Receiving apparatus. A polarized relay 25, Fig. 2, or a pair of relays 35, 36 polarized by rectifiers responds appropriately to the single impulses and controls a ratchet-type relay which controls the lighting circuit. The latter relay may be controlled to switch off through a thermal relay so that only long impulses are effective. In a modification, Fig. 5 (not shown), a polarized receiving relay has a neutral position and controls the lighting circuit through ordinary electromagnetic switches. Fig. 3 shows one of the stations that responds to a characteristic number of impulses. Each impulse of either polarity is repeated by 94 to stepping magnet of 91. A selector switch which on moving off normal starts a synchronous motor which keeps itself running for a slightly longer period than the duration of the 'cycle of the sending motor. If the number of impulses corresponds to a signal appropriate to the station shown, a circuit is made for a thermal relay such as 108 which operates a ratchet-type -relay 105 to change the condition of the lighting circuit and makes a homing circuit for the selector switch. If the number of impulses does not correspond to a signal, the homing circuit is made over springs 101 when the synchronous motor stops. In a modification, Fig. 4 (not shown), thermal relays are not provided and the controlling circuits are made via cam-operated springs controlled by the motor to close a short time after the wiper arm 96 reaches the positions of effective signals. Specifications 518,619 and 518,621 are referred to.