Patent GB-191229387-A (GB)
Title: Improvements in or relating to Telephone Systems.
Filed: 1912-12-20
Granted: 1913-12-18
Abstract: 29,387. Automatic Telephone Manufacturing Co., [Automatic Electric Co.]. Dec. 20. Automatic exchange systems. - In systems such as that described in Specification 26,301/06, in which a group of line switches C, Fig. 1, is controlled bv a master switch D, which keeps them opposite to the terminals of an idle firstselector trunk E, the same trunk is liable to be seized by two line switches in the event of two subscribers lifting down their receivers while the master switch is in motion. To prevent this occurring, an arrangement is provided such that any subscriber who calls while the master-switch is in motion gets a busy signal, and his line switch is locked against operation until he has hung up his receiver. A similar arrangement is applicable to secondary switches F, Fig. 2, interposed between the first and second selectors E, I, and controlled by a master-switch H. Selector circuits. The circuits of the selector E and of the connector (not shown) are the same as in Specification 1421/10. The second selector I is the same as the first selector E with the omission of the relay 82. Line switch C. When the subscriber A bridges his line by lifting down his receiver, the linewinding 8 of the switch C is energized and the armature 18 closes, at the springs 9, 19, the circuit of the pull-in winding 20. If the master-switch is not in motion, the relay 168, in parallel with the motor magnet 40, is not in an energized condition, and the pull-in winding 20 receives current in series with the winding 21 over the springs 22, 23, 24, 25 and the battery lead 17. The line-switch C then operates in the known manner to connect the line 11, 14 to the trunk E, and the masterswitch moves the out-of-nse line-switches opposite the next idle trunk. If however the masterswitch is in motion when the subscriber calls. the relay 168 is energized and a high-resistance relay 169 is in the circuit of the pull-in winding 20, preventing the line-switch C from being operated. The relay 169 closes a circuit for a relay 172, which is individual to the calling line, and which (1) locks itself up, (2) opens the former circuit of the pull-in winding 20, and (3) closes a high-resistance busy-signal circuit through the coils 21, 20, whereby, owing to the inductive connexion of the coil 21 with the linecoil 8, a busy signal is sent back to the calling subscriber. When the subscriber A hangs up his receiver, the relay 172 is unlocked by the opening of the springs 9, 19, and he is then free to attempt another call. A modification is described in which the master-switch momentarily connects ground to all the first-selector wires 63 whenever a line-switch is operated, so as to hold the line-switch in the interval before the selector relays 54, 62 respond. Secondary switch F. When the first selector E seizes the trunk 200, 88, 199, the test-lead 88 is momentarily connected to ground by the slow-release relay 82, which remains energized a moment after its circuit is opened by the side-switch moving to the third position. If the master-switch H is not in motion, the relay 178, in parallel with the motor magnet 177, is not in an energized condition, and the winding 92 of the switch F receives current over the springs 182, 183, 94, 93, 179, 180 and the battery lead 17. The switch F then operates in the known manner to connect the trunk 200, 88, 199, to the second-selector trunk I, and the master-switch H moves the remaining switches of the series F opposite the next idle trunk. The switch F locks itself up in series with the resistance 115, and a holding-ground for the switches F and E is supplied as usual over the test-lead 105 of the second selector I. If, however, the master-switch H is in motion when the trunk 200, 88, 199 is seized, the relay 178 is energized and a relay 181 is in the circuit of the winding 92, preventing the switch F from being operated. The relay 181 energizes a relay 184 which (1) locks itself across the lines 200, 199, (2) open-circuits the winding 92, and (3) connects ground to the wire 88 to hold the first-selector E. The subscriber now receives a busy signal, due to a third winding of the relay 184, and this continues until he hangs up his receiver.