Patent GB-685832-A (GB)
Title: Telephone systems
IPC: H04M3/58
Filed: 1948-08-04
Abstract: 685,832. Automatic exchange systems. AUTOMATIC ELECTRIC LABORATORIES, Inc. Aug. 4,1948 [Sept. 12, 1947], No.20594/48. Class 40 (iv). An incoming call over one of a plurality of exchange lines common to a plurality of substations operates at a first sub-station a visual signal corresponding to the calling line, and the subscriber at the first substation causes a visual signal corresponding to the calling line to be operated at the second substation. In the arrangement described exchange lines 1, 2 are common to substations A, B which are provided with an intercommunication circuit, and line 3 is a line to substation A only. Incoming call over line 1. Relay 280 responds to the ringing current, and intermittently connects up A's buzzer 40 and flashes lamp 41. A lifts his receiver and moves switch K1 to the position indicated by lamp 41, whereupon A is connected to line 1 by relays 220, 300. Relay 210 pulls up and lights lamp 51 corresponding to line 1 at B. If the call is for B, A rotates switch K1 to open contact 45, whereon relays 220, 300 release and connect a holding bridge across line 1, and a pulsing circuit comprising relays 120, 130 flashes lamp 41 to show that line 1 is waiting and to close contact 46, thus connecting up relay 160 which completes circuits for B's buzzer 50 to be intermittently actuated and lamp 52 to be flashed under the control of the pulsing circuit. Relay 170 pulls up over A's loop. B rotates switch K2 to close contact 56 and lifts his receiver. Relay 150 completes the intercommunication circuit between A and B and relay 140 disconnects the buzzer 50 and lamp 52. If B decides to take the incoming call he moves switch K2 to the position indicated by lamp 51 and relay 150 releases to disconnect him from A. Relay 260 pulls up to extinguish lamp 51 and relay 310 follows to connect B to line 1. The pulsing circuit is released, relay 250 operates and 210 falls back, and lamp 41 glows steadily to indicate that B has been switched through to the calling line 1 and that A can hang up. Interim call by B over line 2. B moves switch K2 to close contact 55, and does not replace his receiver. Relays 260, 310 release, the former connecting up the pulsing circuit to flash lamp 51 to indicate that line 1 is waiting and the latter applying a holding bridge across line 1. B is switched through to line 2 by the operation of relays 270, 340 and sets up the call in the usual manner. Relay 240 connects up lamp 43 to indicate to A that line 2 is engaged. To resume conversation over the calling line 1, B, without removing his handset, rotates K2 to close contact 55, whereupon relays 270, 340 release to connect a holding bridge across line 2 and to flash lamp 53 to indicate that line 2 is waiting, and relays 260, 310 pull up to connect B to line 1. Call from B to A. B moves switch K2 to close contacts 56, and completes a circuit for relay 150. Relay 170 operates over B's loop, and the pulsing circuit consisting of relays 120, 130 flashes lamp 42 and operates A's buzzer 40, buzzer tone being inductively reverted to B over a winding of relay 170. When A moves switch K1 to close contact 46, relay 160 switches through and relay 140 disconnects the pulsing circuit. A absent from substation. A moves switch K1 to close contact 49, and relays 100, 110 operate to transfer all incoming calls to B. If B attempts to call A, buzzer tone will not be reverted, thus informing B that A is absent.