Patent GB-373225-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04M5/10
Filed: 1931-02-20
Abstract: 373,225. Semi-automatic and manual exchange systems. STANDARD TELE. PHONES & CABLES, Ltd., Columbia House, Aldwych, London.-(Clemens, P. J. ; 4, Rue Boudewyns, Antwerp, Belgium.) Feb. 20, 1931, No. 5383. [Class 40 (iv).] In a PBX system, the same cord circuits are used by the PBX operator both for completing local connections and for setting up connections over junctions to a main manual or automatic exchange. The additional apparatus for main exchange calls is associated with junction circuits which are split, when released from one call and before the operator has taken down the cord circuit, but are arranged so that the PBX subscriber may be called from the main exchange, or may obtain another connection over the junction without the intervention of the local operator. PBX subscribers may have dials for setting up connections to an automatic exchange after the operator has connected them to a junction. Talking battery is fed from the cord circuits for local connections and from the main exchange for junction calls. Tom may be connected to an established connection if an operator listens in. For night service, any subscriber may be connected to a night jack of a junction circuit. Local calls. When calling lamp EL glows, the operator plugs RP with listening key LK thrown, and battery is fed to the calling line over RS, LK. The operator plugs FP into the wanted line and throws ringing key FRK. E operates over the sleeve of FP and when keys FRK, LK are restored, battery is fed over contacts of E from RS, FS to the calling and called parties respectively. FS extinguishes lamp SL2 which was lit by E. When the receivers are replaced, lamps SL1, SL2 light up. The operator may recall the calling party by throwing ringing key RRK. Call to automatic exchange. The call is taken as described for a local call but with LK thrown, plug FP is inserted into junction jack JJ, Fig. 2. Lamp SL2 in the cord does not glow since the sleeve of JJ is not grounded and E does not operate, but junction lamp JSL glows dimly over a non-inductive winding of JS2 to ground at jack JJ. Coil JHC is bridged across the outgoing junction leads over contacts of jack JJ and when the operator receives dial tone, she throws key DK to operate relay D which connects up her dial. On receipt of ringing tone the operator restores LK thereby connecting subscriber's line over contacts of LK and E (unoperated) direct to the junction. JS1 operates over the junction and energizes JS2 which locks up, extinguishes JSL, and disconnects the bridge over JHC. When the PBX subscriber replaces his receiver, the automatic apparatus is released and JS1 falls back to operate SP which splits the junction circuit. Lamp JSL burns brightly. If the subscriber is to dial, the operator proceeds as before, but restores LK after plugging into JJ without throwing key DK. JS1 and lamp JSL follow the impulses but SP is slow to energize and does pull up. The dialled impulses pass direct to the automatic exchange. After releasing a connection to the automatic exchange, the PBX subscriber may set up another connection if the operator has not taken down the cord. In this case, the junction lamp JSL which glowed on release of the connection is extinguished due to the reoperation of JS1. Incoming calls from automatic. Ringing current operates JL which locks to a contact of the unplugged jack JJ. If the jack had remained plugged from a previous call, JL would not lock and JCL would be flashed. Assuming JJ unplugged, the operator inserts plug FP, which releases JL, lights JSL and bridges JHC across the junction to trip the ringing. After taking the order from the automatic subscriber, the operator plugs RP into the wanted line, restores LK, and rings with key RRK. When the wanted party replies, JS1, JS2 pull up, lamp JSL is extinguished, and bridge JHC removed. The operator may first offer the call before connecting through, and for this purpose presses DK to operate D which opens the junction. Secrecy. If the operator attempts to listen to a local connection, ground on a first-operated contact a of key LK completes a tone circuit from BZ over a special winding W1 of the induction coil and contact of FS. This is heard by the operator and both parties to the conversation. In the case of a junction call, the ground from a passes over a non-inductive winding of E to relay T which connects ground from the operated contact of JS to lead TC to complete the tone circuit. Relay D, being marginal, is not operated with T. Relay T also connects up bridge JHC to hold the automatic switches. Night service. A regular cord is plugged into NJ, Fig. 2, and into a subscriber's line, and a subscriber thus connected may call and be called from the main exchange. Junctions to manual. The junction circuit for a central battery manual exchange may be the same as in Fig. 2 with dial relay D omitted. If, however, it is desired that a PBX operator may offer an incoming call, a relay D is operated by a key to disconnect the junction from the junction circuit and connect it to a holding bridge. If the exchange is a local battery one, the junction circuit shown in Fig. 3 is used, This operates similarly to Fig. 2 except that relay D connects up a ringing source for calling purposes and relay JS1 feeds battery to the local party.