Patent GB-355927-A (GB)
Title: Improvements relating to automatic telephone systems
IPC: H04Q3/00
Filed: 1930-08-11
Abstract: 355,927. Automatic exchange systems. SIEMENS BROS. & CO., Ltd., Caxton House, Tothill Street, Westminster, DIXON, R. G., 162, Westmount Road, Eltham Park, and PATTERSON, W. G., 68, Eltham Road, Lee, all in London. Aug. 11, 1930, Nos. 23964/30 and 3358/31. [Class 40 (iv).] In a small exchange system the connector comprises a single motion switch which moves equal steps for each impulse in the two trains to which it responds and which for some first digits moves to a position corresponding to the sum of the two digits whilst for other first digits it moves to a position determined by adding the impulses in the second digit to a number determined by the first digit. The switch may have two sets of wipers, the set selected depending on whether the first digit is odd or even. Certain subscribers are given breaking-in facilities and a conference circuit and code-calling facilities are provided. Tones and ringing current are generated by a relay combination as and when required. As described, connections are established over link circuits comprising line fingers and connectors, the link to be used being selected by a relay allotter, the connectors being designed to serve 25 or 50 lines, the latter embodiment being detailed below. Seizure of link and connection to calling party. When a call originates L and ST operate in series, L operating lI only and ST pulling up. The start circuit is thus completed over S11, energizing S. FDM drives the finder in search of the calling line and, when this is found, CD energizes in series with L which pulls up completely. CD enables A to energize, BA operates and BB switches the link through to the calling line. CD releases. If no other line were calling when L pulled up ST would fall away. In this case AB in the allotter would energize in series with AA and lock-up. The next call would seize the link over S13 and when ST again released AC would energize to connect the start lead over S15 after which SI1 would again be used. Three of the six link circuits provided are thus allotted for use in turn, the other 3 are used if two lines call simultaneously or if the selected link is in use. If, for example, when L energized, a second caller had been waiting, ST would have remained up and when BB energized the start lead is extended over SI1, SO1 to the next link and if this is engaged the start circuit passes over contacts in the second link equivalent to bb5 or on5 to SO2 and SI3. The windings of AA, AB and AC are in opposition so that when AA (1) and (II), AB (II) and (III) and AC (1) and (II) respectively are energized together, the relay releases. Setting of connector. On the operation of A relays C, BA, BB, CS pull up, and relay CS completes a buzzer circuit for R which generates dialling tone. The caller, hearing this tone, dials the number of the wanted party. The lines are numbered 12, 21 .. 26, 31 . . 34, 70 .. 99 and 1 .. 09, those lines having odd first digits being reached over CON 3, 4, 5, the remaining lines being connected to banks CON 6, 7, 8. For first digits 1, 2, 3, 7 or 8 the contact to which the wipers are set is that representing the sum of the two digits dialled. Relay A repeats the first digit to CDM, to step the connector, and to relays P, Q. As soon as the switch moves off normal, relay ON operates and locks up. The windings of relays P, Q are in opposition so that these relays operate on each odd digit and release on each even digit. Consequently when the train ceases either wipers CON 6, 7, 8 or CON 3, 4, 5 are connected up, depending on whether the digit is even or odd. If the first digit is 1, 2, 3, 7 or 8 relay A remains operated at the end of the train and C releases. TR pulls up and locks and C re-operates. The second impulse train is repeated by A to CDM, S energizing on the first pulse and locking. The relays P and Q are not operated. At the end of the train the wipers will be resting on contacts the number of which is that of the sum of the two digits dialled, the line connected depending on whether P and Q are up or down. C releases and, if the line is free, H operates and TR and S release. CS re-operates starting up buzzer relay R and cyclically operating relays SA, SB, SC. Ringing current, broken up by SB, is fed over R135 and TR to the calling line, this current being fed over R246 to links 2, 4, 6 when required. Tone is fed back to the calling subscriber. When the called party replies TR energizes and switches through, speaking current being fed from A to both parties. If the line had been busy it would not have energized and busy tone, generated by BT and broken up by SC, would have been fed to the caller. If the first digit had been 9 or 0, CON2 would have found earth and the connector would have been stepped rapidly to the 17th or 18th contacts respectively and further movement of the switch would have been as described above. Last party release is provided ; A falling away when both parties have cleared causing the release of all operated relays. The connector steps to normal over CON1. Breaking-in on engaged line. If a caller has the privilege of entering an engaged circuit he is provided with a key PK one side of which is wired to his contact in finder bank FDR2. When the subscriber hears busy tone he may press key PK which energizes H over winding (II). S releases and TR pulls up over the already closed loop allowing the caller to enter the circuit. Conference facilities. The line circuits of subscribers with conference facilities are connected through contacts of a relay CF, winding (1) of which is connected to the subscribers' number in FDR1. To enter the conference circuit the subscriber dials the appropriate number and H pulls up in series with CF (1). Relay CF removes the subscriber's instrument from the line circuit to release the link and locks over the subscriber's loop. Individual feed circuits are provided and each caller may enter or leave the circuit at any time. The connection of lines to a conference relay feed is made over jacking contacts which close when the set is removed from the rack. Calling subscribers absent from their telephones. Contact 19 of CON2 is connected to earth and consequently if this line is tested and H operates, TR remains held and ringing is not connected. A further impulse train can thus be transmitted directly to the equipment to transmit a bell or other sound signal to all subscribers' stations.