Patent GB-583834-A (GB)
Title: Improvements relating to telephone systems
IPC: H04Q3/00
Filed: 1945-05-25
Abstract: 583,834. Automatic exchange systems. SIEMENS BROS. & CO., Ltd., and LONG, D. P. May 25, 1945, No. 13183. [Class 40 (iv)] In a line finder system in which the group of lines served by a group of finders is divided into two or more subgroups, on the initiation of a call, a free allotter executes a testing operation to determine the relevant subgroup. If different groups of finders are served by common allotters, the test determines the group as well as the subgroup in which the calling line is situated and the allotting operation is restricted to finders serving that group. As shown, each 200-line group is divided into four subgroups W, X, Y, Z and the finders are 200- point uniselectors having two sets of double-ended wipers while the allotters are common to four groups of lines. On the initiation of a call, line relay L connects up the appropriate subgroup relay W, X, Y or Z which in turn connects up relay S in all the free allotters serving finders having access to the calling group and marks the calling group. Relay S initiates the operation of a relay chain SA ... SG and prepares circuits for test relays TW and TX over contacts of the chain relays. If the calling line is in subgroup W of the first group, TW pulls up immediately and energizes the allotter start relay ST in series with TS which disconnects the relay chain before SA can operate. Relay CW operates in series with TW and disconnects the S relays, thus releasing the other allotters. In the case of subgroup X, relay TX operates with similar effect. In the case of subgroups Y, X, however, TW or TX pulls up after SA has operated and the resulting operation of TS locks SA. If the calling line is not in the first group, the chain relays SB ... SG operate in succession in order to test the succeeding groups, and when a starting condition is found the last relay to operate locks, the locking circuits for SC, SE, SG including also the preceding relay and SA. Relays SB, SD, SF mark bank 8 of the allotter in order to limit the search to finders of the appropriate group, and, in order to minimise the search time the bank contacts may be connected to finders of different groups in rotation. The allotter seizes an idle finder in the usual manner and this then hunts under the control of test relay P in the allotter, which is connected to the appropriate test wiper of the finder by relay SA. Upon operation, relay P connects up the corresponding switching relay HA or HB. If in the course of its search the allotter passes through its last position, relay LC energizes and makes a circuit for stopping the allotter should it reach that position a second time on an unsuccessful search. Holding of the allotter for an excessive time results in the operation of relays PS, PZ which close alarm circuits and bring about forced release. For testing purposes an artificial call may be set up by bridging the middle and one of the outer springs of a test jack to operate relay WX in series with W or X or relay YZ in series with Y or Z, the first position in the relevant subgroup being marked in the finder banks. If a call is made during testing, WX or YZ is released by short-circuiting.