Patent GB-313596-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1929-05-15
Abstract: 313,596. Associated Telephone & Telegraph Co., (Assignees of Bellamy, J. I.). June 15, J.928, [Convention date]. Automatic and semi-automatic exchange systems.-In non-numerical switching arrangements comprising a group of secondary line-switches of the plunger type controlled by a master switch, when any one of the trunks incoming to a group is seized, the remaining trunks are marked busy until another outgoing trunk has been preselected. This arrangement prevents seizure of one or more additional switches after a line switch has been seized and before the remaining trunks are rendered busy. In the case of switches of the kind in which the plunger returns, immediately on release of a connection, to the control of the master switch without waiting to be picked up by the master switch, the incoming trunk is maintained busy by the line-switch for a time sufficient to enable the plunger to return. The invention is described as applied to a system in which a connection is extended over one of the levels of a group of selectors and groups of secondary line-switches to trunks outgoing to a distant office. On seizure of the trunk 2, 4 leading to the line-switch SLS, ground from the preceding selector is connected over conductor 3 to common conductor 39 and busies the whole of the line-switches of the group. Relay 34 of the common group C pulls up and connects holding ground from the contact of normally energized slow release relay 33 the function of which will appear later. Relay 5 pulls up over its upper inding and the calling loop, locks over its lower winding, disconnects conductor 39 from 3, energizes relay 6, and completes a circuit for the pulldown winding oi magnet 7, the plunger of which completes a circuit over both windings of 7 in series. The connection now extends to repeater R at which line relay 25 energizes to loop the outgoing conductors 27, 28. Ground from 10 over wiper 37 of the master switch M operates start relay 35, and M hunts for the next idle trunk. Relay 35 also grounds conductor 38 to energize common relay 31 which closes a fresh locking circuit for 34 and energizes 32 to open the initial locking circuit. When the master switch finds an idle trunk, relay 35 falls back followed by 31, 32 and 34 so that busy ground is removed from common conductor 39 and the incoming trunks, other than that shown, are available for service. Relay 34 is adjusted to fall back before 32. Release. When the calling party replaces his receiver, relays 25, 26 fall back, the preceding selectors are released, and relay 5, which has been locked to the release wire 3, de-energizes and connects temporary ground from a contact of 6 to the release wire to guard the trunk 2, 3 during the restoration of the plunger of SLS. If the plunger is not self-restoring, relay 6 is omitted. All outlets busy. Stop relay 36 of the master switch operates in a chain circuit over contacts of relays 26 - - 26<1> at the repeaters, and as wiper 37 does not encounter an unguarded contact, relay 35 remains operated and maintains relays 31, 34 energized to the common guard conductor 39. Defective circuits, arrangements for dealing with. The slow-release relay 33 controlling the initial looking circuit of relay 34 prevents this relay from being permanently locked and busying the groups of line-switches in the case of an accidental ground, temporary or permanent, on release wire 3.