GB224692A - Improvements in or relating to automatic and semi-automatic telephone systems - Google Patents

Abstract

224,692. Coventry Automatic Telephones, Ltd., and Collyer, J. E. Oct. 20, 1923. Automatic exchange systems.-The circuits of a line-switch of the " normal " type are such that, during release, the line tests free, but should it be seized by a final selector at this time, the cut-off relay is unable to operate until the restoring movement is completed. The line relay, upon energization, completes circuits for the cut-off relay and for the stepping magnet, the latter circuit which prevents the operation of the cut-off relay, being rendered ineffective as soon as the switch moves into a selecting position so that the continued stepping of the switch depends upon the potential upon the test contacts engaged by the test wiper. Outgoing call. When a calling subscriber removes his receiver, his line relay 1. Fig. 1, immediately grounds the incoming test lead 18 and completes a circuit over the test wiper 6 and its normal contact 10 for the stepping magnet 3. At the first step, this original energizing circuit is disconnected, but magnet 3 remains energized over the test wiper 6 until an idle trunk is found when the cut-off relay 2, which has hitherto been short-circuited, energizes in series with magnet 3, which does not operate further, and cuts off relay 1. At the end of the connection, the removal of ground from the test conductor by the switch ahead, de-energizes relay 2 which completes a restoring circuit for magnet 3 over contacts 16, 19 and off-normal contacts 9. Incoming call. If the line, Fig. 1, is idle when seized by a final selector, Fig. 2, the release of the units series relay 55 completes a circuit for the switching relay 53 in series with cut-off relay 2 and magnet 3, and the connection proceeds in the usual manner. If, however, the line-switch, Fig. 1, is being restored to normal, the busy relay 52 does not energize since there is no ground on conductor 18, and relays 2. 53 are prevented from energizing owing to a short-circuit over contacts 16, 19, 9. Upon the complete restoration to normal, relays 2, 53 energize as before and the connection is completed. Dealing with faults. If, on extending an outgoing call, the line-switch seizes a faulty trunk so that no holding ground is sent back over the third conductor, the relapse of the line relay 1 causes the release of relay 2 and establishes the stepping circuit 3, 16, 19, 9. Relay 1 again energizes, but is slow to operate so that the switch has time to advance one step to free itself from the faulty trunk before its stepping circuit is broken at contact 16.