Patent GB-322239-A (GB)
Title: Improvements in or relating to automatic or semi-automatic telephone systems
IPC: H04M7/10
Filed: 1928-09-05
Abstract: 322,239. Standard Telephones & Cables, Ltd., and Wright, E. P. G. Sept. 5, 1928. Automatic exchange systems.-In a bi-directional selector having access to groups some of which comprise more than 10 lines, the extra lines of the groups of more than 10 lines are accommodated on spare positions in one or more levels used for groups of less than 10 lines. The selector is temporarily associated with a bi-directional control switch which is common to a group of such selectors and in which the extra lines are connected to the level corresponding to that in which the main lines of the group appear in the selector, so that the two switches are enabled to hunt simultaneously over the main lines and extra lines. If the selector finds an idle line, the control switch is released. If the control switch finds an idle line and the selector does not do so, the latter restores and re-operates under control of the control switch to make connection with the seized line, a temporary connection to the next switching stage being made meanwhile over wipers of the control switch. Selected group occupies a single level. Upon seizure, relay K energizes in series with relay 2 and associates the control switch with the selector. Line relay 1 energizes and connects up relay 9, and impulses are repeated at contacts 2 (1), 1 (1) to vertical magnets VI, V2, slow-release relay 3 being energized at the first impulse and holding throughout the train. Relays 6, 7 energize and lock over interrupter springs of rotary magnets R1, R2 respectively. When relay 3 falls back, rotary magnet R1 takes a step and breaks the circuits of relay 6, and if the first line is busy, relay 4 pulls up over the test wiper and interacts. with magnet R1 to hunt over the selected level. Meanwhile rotary magnet R2 takes a step and breaks the circuit of relay 7. Where the group occupies a single level, all the positions in that level are artificially busied in the control switch, and relay 7 reoperates over the test wiper and interacts with magnet R2 until the 11th position is reached. If the selector finds an idle line, test and switching relay H energizes in the usual manner, being no longer shortcircuited, and the control switch is released, the restoring circuit being controlled by relay 2. If the group occupies less than the full level, the next position is left blank, and relay H operates if this position is reached, but relay 1 remains held over the line terminals and relay 5 energizes over the test terminal and connects up busy tone. If the group occuplies the whole of one level, cam springs S operate at the 11th step and busy relay 5 energizes thereover. Selected group occupies more than one level. The control switch hunts over the extra lines while the selector hunts over the main lines in the selector level. If the control switch finds an idle line, test relay O energizes in series with relay 7 in the usual manner, but if the selector also finds an idle line, the control switch is released as described above. If the selector finds no idle line, cam springs S are operated and relay P energizes and locks, connecting up release magnet Z1 to restore the selector, releasing relay 9 and extending the incoming line over the seized line. Relay O is locked at the next selector and holds relays 2, K. A circuit is now closed for vertical magnet V1 in parallel with magnet SM of a single-motion switch with two banks S1, S2, terminals of which are marked respectively by wipers D, U of the control switch according to the position of the latter. The selector is therefore raised until relay 8 energizes over bank S1, operating relay Y partially and closing a restoring circuit for magnet SM. Relay Y then operates fully, a short-circuit on its winding being opened at contacts SN, and disconnects relay 8, whereupon relay 4 pulls up and interacts with rotary magnet R1 and magnet SM until the seized line is reached, when relay 8 energizes over bank S2, disconnecting relay 4 and connecting up switching relay H. If the control switch finds no idle line, cam springs CS operate, and busy relay energizes over springs S, CS. Specification 320,905 is referred to.