Patent GB-254046-A (GB)
Title: Improvements in automatic and semi-automatic telephony
IPC: H04Q3/42
Filed: 1925-04-17
Abstract: 254,046. Standard Telephones & Cables, Ltd., (formerly Western Electric Co., Ltd.), Moir, R. A., and Hartley, G. C. April 17, 1925. Semi-automatic exchange systems.-In a system in which a coder associated with the outgoing end of an inter-exchange trunk receives impulses from a register-controller of the code-translating type and re-transmits them as code impulses to control a number indicator at a distant manual exchange, the relay group with which is associated the hunting switch which selects an idle coder is provided with means for testing a seized coder as regards its operative condition and the transmission of impulses from the register-controlled is delayed until a coder which is both idle and also operative has been selected. The invention is described with reference to two different relaygroups the first of which acts also as a repeater and is provided with feed, supervisory and busyflash-repeated arrangements, whilst in the second the line circuits extend straight through and the connection is held from a preceding switch. First arrangement. When the repeater shown is seized, relays A, BA, B operate, the circuit of relay A including a winding of a shunt-field relay in the register-controller which operates and prevents the transmission of impulses. Relay S operates over its lower winding and connects magnet DM over contacts S10, K16, S5 to the test wiper of the coder selector, so that hunting takes place until an idle coder is found, when relay K operates in series with magnet DM. Relay K breaks the original circuit of relay S, but the upper winding of the latter is connected over contacts CF8, A6. K5, to the impulsing lead of the coder on which battery will normally be found. If this battery is not present, relays S, K release, magnet DM operates over contacts S8, CZ9, BAS, and when relay S operates again over its lower winding, the wipers are stepped on to the next coder. Hunting thus continues until an idle and operative coder is found. When battery is found on the impulsing lead, relay S remains operated and slow-acting relay CF then energizes and reverses the incoming connection so that the shunt-field relay in the register-controller releases and impulses are sent out. These are repeated by relay A over the circuit BA8, A6, K5 to the coder. When coding is completed, relay CZ operates over contacts CF8, A6, K5, releases relays S ,K and the coder and switches through. Relay I operates from battery and earth at the manual end and, when the called subscriber replies, relay D also energizes and releases relay CF producing a further current reversal for supervisory purposes. If the called subscriber is busy. the interrupted battery connection to the lower talking conductor at the manual exchange effects successively the partial and complete operation of relay BF and succeeding energizations and de-energizations of relay I are repeated over the incoming trunk as intermittent earthings of the lower line conductor over contacts BF8, 16, CZ6, K13, BA8. In the case of premature release by the calling subscriber relav B remains' held over its lower winding and the lower outgoing talking conductor to mark the relay group busy until the connection is released at the manual exchange. The interval between the relapse of relays BA, Q serves to effect the release of the preceding switches. Second arrangement. This is very similar to that described above, but the relays Q, D, I and BF are eliminted, and the only relay operated in the relay group during conversation is the relay CZ which remains locked to the incoming test conductor and completes a metallic connection between the incoming and outgoing talking conductors. In the case of a premature release, relay CZ releases, but relay B operates to ground the incoming test wire. Specifications 253,583 and 256,295 are referred to.