Patent GB-375326-A (GB)
Title: Improvements in or relating to automatic switches for use in telephone or like systems
IPC: H04Q3/00
Filed: 1931-03-23
Abstract: 375,326. Automatic exchange switches. AUTOMATIC ELECTRIC CO., Ltd., Strowger Works, and TAYLOR, R., 30, Oulton Road, Wavertree, both in Liverpool. March 23, 1931, No. 8920. [Class 40 (iv).] In a group selector switch adapted to test two outlets substantially simultaneously, the relay which holds open the hunting magnet circuit during directive movement is differentially wound and is adapted to interact with the hunting magnet to effect stepping and to act as the test relay in such a manner that in the event of both outlets in any particular position being unavailable both windings of the relay are energized to effect its release and thereby facilitate further stepping. As shown, when the switch is taken into use, line relay 1A is operated and relay 1B is energized to earth the guard wire 22, prepare the circuit of the vertical magnet 1VM and change-over relay 1C in parallel and prepare the circuit of the rotary magnet 1RM. When the relay 1A is impulsed by the incoming impulses, the vertical magnet is operated to raise the wipers to the desired level and the relay 1C is energized and maintained operated during impulsing over a short-circuited path including its lower winding and contacts 1c1. At the conclusion of impulsing, 1C releases and energizes rotary magnet 1RM to advance the wipers into engagement with the first set of bank contacts in the selected level. The rotary off-normal springs 1NR1 are operated to open the short-circuited path of the lower winding of relay 1 C and prepare the circuit of test wiper 2P and springs 1NR2 open the circuit of the vertical magnet and prepare the circuit of the upper test wiper 1P. In the event that the first two lines are busy, earth on the test wipers 1P, 2P prevents operation of switching relays 1HA, 1HR, and when the rotary magnet springs 1rm close, relay 1C is operated over its upper winding and looked over the off-normal contacts 1N1. Relay 1C de-energizes magnet 1RM and completes a circuit for its lower winding from test wiper 2P. When both windings are energized the relay is released and rotary magnet is again operated. This interaction between the relay 1C and magnet 1RM is continued so long as the wipers 1P, 2P encounter busy outlets. When wiper 1P encounters a free outlet, absence of earth on the test contacts permits operation of relay 1HA without operation of relay 1C. Relay 1HA opens the circuits of the rotary magnet 1RM and switching relay 1HB and switches through the speaking conductors to wipers 23, 24. In the event however that the wiper 2P first encounters a free outlet, relay 1C is operated over wiper 1P as already described and relay 1HB is energized to perform functions substantially identical to those associated with relay 1HA with the exception that the speaking conductors are switched through to wipers 25, 26. When all outlets are busy, cam springs are operated in the eleventh position to operate the overflow switch 10VF and effect the alternate application of busy tone and flash battery through the lower winding of relay 1A to bank contacts 27, 28.