Patent GB-688615-A (GB)
Title: Improvements in or relating to electrical signalling systems
IPC: E21F17/18
Filed: 1949-02-07
Abstract: 688,615. Electric selective signalling. ERICSSON TELEPHONES, Ltd., and STEVENS, J. R. H. Feb. 6, 1950 [Feb: 7, 1949], No. 3267/49. Class 40 (i). In a mine haulage system " stop," " start " and other signals may be initiated at any of a plurality of substations over local conductors and transferred therefrom over common conductors to a central station, and the circuit arrangements are such that when a " stop " signal is received from a substation the central station will respond to a subsequent "start" signal only if it is sent from the same substation. Common insulated conductors, W1, W2, W3, W4 lead from the central station, Fig. 1, to the various substations as shown at Fig. 2, Fig. 3, which are provided with local bare conductors AS1, AS2, BS1, BS2. These bare conductors are bridged by a suitable tool to send signal impulses, a " stop signal comprising a "long" impulse e.g. of two seconds minimum duration and a "start" signal two " long impulses separated by a short interval. Other information signals may also be sent by short impulses suitably coded. At the central station relays B, H, are normally energized and the start lamp TLP lighted. Initiation of a signal impulse at any substation, e.g. by bridging lines AS1, AS2, causes energization of relay S at the central station in series with the left-hand low resistance winding of relay AR at the operative substation. Both relays operate and relay S operates a relay A and de-energizes relay B which is however held operated by a normally charged condenser C1 for a time slightly less than the minimum duration of a long signal. Relay A reverses the polarity of the line connections from battery BX but the direction of current through the operated relays S and AR remains unchanged by virtue of the various rectifier connections shown and the closure of contacts AR1, AR2. Relay A also operates a bell relay RB to ring parallel connected signal bells PBL, ABL, BBL, at the central and all substations. These conditions obtain while the signal is being sent. If the signal is of short duration the removal of the bridging across the bare wires AS1, AS2 releases relays AR, S, A, RB, before B has released, whereupon B is re-energized from the battery, the condenser Cl is rapidly charged over R3, and the circuit is again at normal. Signalling by coding arrangements of short signal pulses may thus be effected. If a "stop" signal (one long ring) is sent, relay B releases before the end of the signal, whereupon a relay CA is energized to light the " stop lamp PLP and release relay H to exting- uish the start lamp TLP. At the end of the signal relay A is held at CA2 to maintain the reversed polarity connections to the line and relay AR holds over its right-hand high resistance winding. Relays S and RB, however, relapse to silence the signal bells. As S releases, relay B is reoperated and a relay D energizes in series with operated relay CA over contacts G1 and a normally closed reset key KT. Relays A, B, CA, D at the central station and relay AR at the operative substation, Fig. 2, remain operated until a " start" signal is sent from this station, and during this interval audible messages may be sent from any of the substations by coded short impulses, the bell relay RB being operated over the rectifier AMF, BMF, &c. at the signalling substation. If a spurious " start " signal is initiated from a substation other than the one which originated the effective " stop " signal, the bell relay RB operates to give the audible portion of such a signal but has no other effect so that the " stop lamp PLP remains lighted. When a "start" signal (two " long " rings) is initiated from the pertinent substation, Fig. 2, relay S operates for the duration of each ring. Relay B as previously described releases before the end of each ring. On the first release it energizes a relay E, and a relay F operates in series with E at the end of the ring. Relay F operates the start buzzer TBZ. On the second release of relay B a slow-to-release relay G operates, and at the end of the second ring, relay S releases and causes all relays to revert to normal. The relay H is made slow-to-operate, by the capacitor C2 and neon lamp N, to delay lighting of the start lamp TLP, however, so that a further " stop " signal may be effectively received before the central operator restarts the haulage system. A ring key KG enables audible signals to be sent from the central station, and the reset key KT may be operated to reset to normal should an incomplete " start " signal be received.