Patent GB-297747-A (GB)
IPC: H04M5/10
Filed: 1928-09-25
Abstract: 297,747. Associated Telephone & Telegraph Co., (Assignees of Crocker, T. F.). Sept. 26, 1927, [Convention date]. Semi-automatic exchange systems. - A cord-circuit, particularly for a semi-automatic toll-operator's position, comprises the following features:- (1) The operation of the talking key K10, Fig. 1, individual to the cord associates the common equipment, Fig. 2, including the headset and dial, with both ends of the cord, the operation of one of the dialling keys K4, R5 serving in conjunction with offnormal springs of the dial to break the connection to one end of the cord and to render the dial springs operative to transmit impulses over the other end. (2) A relay 207, operated as soon as the tip of the plug P2 engages the tip of the jack J2 and before the ring circuit over the plug and jack is completed, short-circuits the receiver of the headset to prevent a click being heard during the insertion of the plug. A similar shortcircuiting of the receiver takes place during impulsing. (3) The operation of a common key PB, Fig. 1, prepares the circuit of a timing device 109, the circuit being completed by the restoration of the talking key K10 when conversation commences so that after the conversation has lasted for a predetermined time a signal is given to the operator by the flashing of the supervisory lamp 112. Operation of cord-circuit to complete a toll call. The arrival of ringing-current over the toll junction on the left of Fig. 1 energizes relay 101 and lights lamp 103. The toll operator inserts plug PI and throws key K10 which operates relay 108 so that both ends of the cords are connected to the operator's common equipment, Fig. 2, and the operator is informed of the wanted number. One or other of the dialling keys K4, K5 may be left thrown and assuming that K4 is thus thrown, the engagement of the tip of the plug P2 with the tip of the jack J2 of a toll-service trunk 120, 121, completes a circuit from earth over sleeve relay 115, sleeve of jack and plug, lead 136, key K4, for the upper winding of relay 207 which short-circuits the headset receiver, this operation taking place before the ring conductors of the plug and jack come into engagement. Relay 207 also operates relays 206, 205, the latter locking to lead 136 and opening the circuit of relay 207. Relays 207, 206 release after an interval, the former having been made slow to release by a short circuit around its lower winding closed by relay 205. Sleeve relay 115 also operates closing a bridge across conductors 120, 121 including relay 119 which on operating closes a parallel bridge through resistance 118. When the dial CD moves off normal, springs 231, 232 re-energize relays 207, 206 to short-circuit the headset receiver and the condenser in series with the impulse springs, whilst at the same time springs 232, 233 energize relays 209, 201, the latter disconnecting the dial from the lefthand side of the. cord. Relay 209 opens the sleeve circuit releasing relays 115, 119, whereby the condensers in the conductors 120, 121 (provided to prevent the starting of the ringing arrangements in the toll-service final selector by stray ringing-currents) are short-circuited and a through metallic circuit is established. When the dial returns to normal, relays 115, 119 reoperate whilst relays 207, 206 fall back slowly, maintaining the short-circuit around the receiver until the group-selector hunting operation is completed. If the called line is idle, a reversal of current across conductors 120, 121 energizes polarized relay 116 which short-circuits the upper winding of relay 115. The operator, not hearing the busy signal, restores key K10 whereupon lamp 112 lights in series with the lower winding of relay 115. The throwing of ringing key K9 inserts resistance 114 into the sleeve circuit to extinguish lamp 112 and release relays 115, 119. Ringing current now passes over conductor 120 to start the ringing operations at the final selector and at the same time earth is connected to the lower conductor 121. When the ringing key is restored relays 115, 119 re-operate and lamp 112 is lit. When the called subscriber replies, battery is disconnected from inductors 120, 121 (there being no feed to these conductors during conversation) so that relay 119 releases and removes the short-circuit around the upper winding of relay 115 thus extinguishing lamp 112. If the calling subscriber releases first, the transmission of ringing current over the incoming junction energizes relay 107 which causes the operation of relay 106 over the answering sleeve circuit and the lighting of lamp 105. Coin-freed systems. - Common keys K1, K2, K7, K8 associate coin-collecting or coin-refunding battery with the tip conductor of one or other end of the cord, in conjunction with the cordsplitting relays 201, 204 which complete the connection to the tip conductor and open the ring conductor. The keys also open the sleeve circuit so that. relays 115, 119 release and short-circuit the trunk condensers to provide a metallic circuit for the coin-controlling battery. Time indicators.-In order to time a connection the operator, with the key K10 thrown, presses common key PB energizing relay 111 which locks to the sleeve circuit. When key K10 is restored a circuit is completed for the dashpot relay 109 which after three minutes, say, connects up interrupter F to flash the supervisory lamp 112. The throwing of key K10 to inform the subscribers releases relay 109 so that if the subscribers wish a further period the mere restoration of key K10 starts the timing operation again. Specification 283,853 is referred to.