GB265695A - Improvements in automatic and semi-automatic telephone systems - Google Patents

Abstract

265,695. Standard Telephones & Cables, Ltd., Moir, R. A., and Hartley, G. C. Nov. 13, 1925. Automatic and semi-automatic exchange systems.-A discriminating selector at a district office has an associated non-numerical switch which, when the selector is taken into use, seizes a trunk to the main exchange. The first train of dialled impulses are received by a repeater at the outgoing end of the trunk, and are repeated thereover and also back to the selector. If the first digit indicates a local call. shaft springs are operated which cause the selector to drop hack and the trunk to be released. The impulse relay is connected directly to the calling loop, and the connection is then set up in the usual manner. If all the trunks are busy, the non- numerical switch comes to rest on the last terminals, and circuit changes take place by which the impulse relay of the selector is connected to the calling loop, so that a local connection may be established, while a busy signal is sent back if a main exchange connection is desired. Main exchange call. Line relay L upon energization grounds the test wire and connects up the magnet DM and switching relay K of the hunting switch. Relay K energizes when an idle trunk is found and extends the calling line to the associated repeater. Impulse relay A energizes over wiper Q connecting up relays B, C, and responds to the first train of impulses, and the vertical magnet V operates. No circuit is closed for the rotary magnet K when relay C falls back, so that further trains of impulses have no effect in the selector. Local call : In this case, shaft springs NPA are closed, and when relay C falls back, two-step relay SW energizes partially and closes contacts 5, 6, connecting up the release magnet Z to restore the selector. Relay SW energizes fully when springs NPA re-open, breaks the connections to the repeater so that the trunk is released, and connects impulse relay A to the calling loop. Relay C re-energizes, and the selector operates in the usual way as a group selector. Test relay H upon energization closes a fresh circuit for relay SW. If all the outlets are busy, eleventh step contacts S are closed and a busy signal is sent back. All trunks busy. Relay K energizes over the last test terminal of the hunting switch, which is ungrounded in this case, and connects impulse relay A to the calling loop over the line wipers of the hunting switch. Relays B, C energize and dialling tone DT is sent back. Relay C falls back after the first impulse train, and if a main exchange call is required, a busy signal BT is sent back. If the call is a local one, springs NPA are closed, and the call proceeds as described in the last paragraph. Special service calls by dialling O. Springs NPB are closed on the tenth level, and relay SW energizes fully and connects up rotary stepping relay G, so that when relay C falls back, the selector hunts for an idle trunk leading to an operator's position.