GB249316A - Improvements relating to telephone systems - Google Patents

Abstract

249,316. Siemens Bros. & Co., Ltd., and Berry, J. March 17, 1925. Automatic and semi-automatic exchange systems.-A clearing indicator at a manual operator's position is operated when an automatic subscriber hangs up by the application of alternating current for an interval determined by a mechanical timing device, comprising a rotating cam 10 controlling springs 11, 12, 13. Fig. 1 shows a trunk from a manual exchange terminating in a group selector at an automatic exchange, and having a special dialling jack JJ. Upon release by the called subscriber, relay Y falls back and prepares a circuit for a relay Z, which is completed over spring 12. The relay S locks over winding 2, connects up alternating current RG to operate the indicator RO, and prepares a circuit for a relay Z, which is completed over spring 13 and winding 3 of relay S. Relay Z locks and opens the holding circuit of relay S, so that it is subsequently released at spring 13. Line relay A is held at front contact s' to prevent release during this operation. Fig. 2 shows a trunk accessible from automatic switches and leading to a manual exchange. Relay N operates when the trunk is seized and connects its high resistance left winding to the test wire c. Ringing current RG is transmitted to operate the calling signal CL, a ringing signal being sent back from transformer RS, and when the distant operator plugs in, ring cut-off relay TR energizes, locks and connects up relay E. When the calling subscriber hangs up, relays N, TR fall back, and relay E is now held over the trunk loop. Relays S, Z energize in turn under control of the cam 10, as in Fig. 1, to operate the clearing indicator RO by alternating current RG<1>. Relay E marks the trunk busy during this time at open contact e<1>. Specification 233,859 is referred to.