Patent GB-307537-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1927-12-09
Abstract: 307,537. Automatic Telephone Manufacturing Co., Ltd., Vick, W. S., and Turton, G. D. Dec. 9, 1927. Automatic exchange systems.-In a system employing call finders and having subscribers' lines provided with permanently connected line relays, calling is effected by intermittently short - circuiting the wanted subscriber's line which causes his bell to be rung by discharge of the condenser bridged across the line in series with the bell. Subscribers' lines are provided only with individual line relays, and the circuit, completed by the energization of a line relay, for starting up a finder, is rendered ineffective in the case of an incoming call. The invention is described with reference to a small system in which calls are set up over finder-connector links. Line relay L at 10 grounds guard conductor 70 extending to the fourth bank of connector CS, at 12 removes ground from fifth bank of FS to mark the line calling, and at 11 completes a circuit from battery over 73, 78, 60 for start relay DX of allotter D. Relay DY now energizes in series with magnet DM3, which remains inoperative, and at 79 extends ground over 83, 62 to relay A (lower) which at 27 prepares a circuit for B and at 29, 30 completes circuit for finder magnet DM1 over wipers 64, 65 to ground on non-calling and busy lines respectively. When the calling line is reached, relay B operates in series with the magnet, locks itself over 16, 19, extends busy ground from 18 over wiper 65, this ground being extended over conductor 69 to the first bank of CS, and at 15 prepares the impulsing circuit. Ground over wiper 65 and 11 short-circuits DX the relapse of which is, after an interval, followed by DY, and during the interval the allotter is stepped on by DM3 over 100, 75, DX being free to operate if another call is pending. Relay A is now held over its lower winding, wiper 48, lower winding of C, wiper 49 to ground at 17, C remaining inoperative. Common conductor 61 is grounded at 20 to complete a circuit for self-interrupting tone relay BU and to energize timing relays M, N, P in a manner and for a purpose to be described later. Tone, induced in lower winding of BU is sent back over 57, 46, 102, 24 to calling subscriber who commences to dial, the impulses being transmitted over 10, 66, 15, 26 to magnet DM2 which steps CS on to the wanted line. Relay A is held over its upper winding during the passage of impulses. If the wanted line is free, ringing relay C (lower) energizes over homing plate and wiper 49, 44, 22, 45 to battery on conductor 50 which corresponds to calling sub. scribers conductor 69. Relay C prepares at 32 and 33 respectively circuits for D and for its own upper winding which become effective when A restores at the end of the impulse train. Subscribers' lines are numbered 1 to 9, 01 to 09 and 001 to 004. Dialling of digit O moves CS ten steps and A will remain held over wipers 48, 49 in a cirouit previously traced so that C and D do not energize at this time. Ringing current, supply and control of. Relay P energized over common conductor 61, operates N followed bv M which locks itself and causes P and N to be shunted and released in turn followed by release of M. This operation repeats and times the ringing periods. Ringing relay C extends ground from 38 over contact 94 of N and 87 of RX to RY which at 85 operates RX to break the circuit of RY. During the make periods at 94, RX at 86 intermittently short circuits the wanted line over wipers 46, 47 and contacts of C and D. Line relay of wanted line energizes and relapses rapidly, the bell being rung by condenser discharge. The intermittent operation of wanted subscriber's line relay shunts C but makes it slow to release so that it does not fall back during ringing periods, but when he replies, the shunt is maintained and the relapse of C removes ground from 56 to stop ringing and completes the speaking circuit Ground is connected to wiper 45 during ringing, from wiper 49 over O (upper) and subsequently from 17. This ground which extends over a conductor similar to 69 short-circuits relay DX of allotter D to prevent a finder from being started. Release. When calling subscriber hangs up, ground at 12 short-circuits relay B the relapse of which removes ground at 17 to release D and at 20 to release BU, M, N, P, the homing circuit of DM2 being completed at 14. Busy signalling arrangements. Ground encountered by wipers 45, 48 on conductors 50, 54 short-circuits C. On the relapse of A, intetmittent busy tone is sent back from BU over 101, 97. 55 to calling subscriber, the periods being timed by P.