Patent GB-368716-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1930-12-08
Abstract: 368,716. Automatic exchange systems. ASSOCIATED TELEPHONE & TELEGRAPH CO., 1033, West Van Buren Street, Chicago, L.S.A. Dec. 8, 1930, No. 36973. Convention date, Jan. 23. [Class 40 (iv).] Systems in which an allotting switch preselects the next idle call-finder have the following features: (1) The allotter makes a test on the preselected finder when it is actually required for a call and if the test is unsatisfactory a new finder is allotted; (2) When a finder ha.s completed its operation the allotter magnet is energized from the finder over a common multipled lead to advance the wipers one step and if the next finder is busy the magnet is again operated over its interrupter contacts and the test wiper until an idle finder is reached ; (3) The finders are divided into two groups controlled by separate allotters and if a finder in one group takes more than a predetermined time to complete its operation, an alarm is given, the finders and allotter of that group are thrown out of service, and a finder from the other group is selected. If all the finders of the second group become busy the first group is automatically restored to service. The invention is described with reference to a system employing Strowger-type finders with two sets of wipers the subscribers' lines being connected to the levels of the two groups of finders in reversed order and the arrangement being such that a finder in the group in which the calling line appears in one of the first five levels is normallv used. Normal operation. Line relay 201 marks the second level of bank VA and grounds a starting circuit 260 for relay 406 which connects relay 404 over allotter wiper 410. If the finderselector link, Fig. 1, is in normal position and non-faulty, battery potential over resistance 130 is present on lead 179 so that relay 404 operates connecting ground over wiper 409 to operate selector-line-relay 105 and ground over wiper 408 to finder-vertical-magnet 114. Vertical stepping occurs under the control of stepping relay 106 until the marked level is reached when relay 107 operates, transferring the stepping circuit to the rotary magnet 115. If the calling line is found by the lower set of wipers relay 109 operates connecting up switching relay 108 whilst if found by the upper set of wipers relay 108 operates directly over test wiper 231. Relay 108 extends the earth from wiper 408 over multipled lead 181 to allotter magnet 407 which on operating breaks the circuit of relay 403. This removes the ground from lead 181 causing magnet 407 to release and advance wipers 408, 409, 410 one step, the magnet then again operating if necessary over wiper 410 until an idle finder-selector link characterized by the absence of ground is reached. If all the finders in the group are busy, normally-energized relay 405 releases and extends the starting lead 260 over conductor 261 to the allotter of the other group. Faults. If relay 404 does not operate, slowacting relay 403 energizes in series with magnet 407 and by shunting its upper winding with its lower winding permits the magnet to operate to select another finder. If a finder reaches eleventh terminals in any level, cam springs 149 operate relay 108 in series with 106 extending ground to multipled lead 181 and magnet 407 as before. If a finder does not complete its operations within a predetermined time, a slow-operating relay 401 controlled by a vibrating relay 402 connects up alarms 441, 444, and releases relay 405 which extends the starting lead to the other group of finders. If all the finders of the second group should now become busy the release of a relay similar to 405 removes ground from conductor 439 unlocking relay 401 and restoring the first group to service.