GB271142A - Improved circuit arrangements for selectors in automatic and semi-automatic telephone systems - Google Patents

Abstract

271,142. Siemens Bros. & Co., Ltd., and Christian, D. A. Feb. 16, 1926. Automatic and semi-automatic exchange systems.-In a system in which the feeding bridges are at the connector, the back-bridge relay controls both the answering supervisory signal and the busy lamp-flash signal. Selection of wanted line. On seizure, the relays A, B energize in turn. A dialling relay C now energizes over its winding 1 and prepares the impulsing circuit [battery, C(2), VM, e<2>, c<3>, b<5>, a<1>]. When tens impulsing begins, the vertical off-normal contacts k (1, 2, 3) operate and the circuit of C (1) is broken. After impulsing, relay C de-energizes and relay E pulls up over k<3>, c<2>, w<1>, b<3>, completing a circuit at e<5> for C(1) which prepares the ' units ' impulsing circuit. Relay E locks up over k<3>, c<2>, e<1>, b<4>. The rotary off-normal contacts w (1, 2) operate and break the circuit of C (1). At the end of train, relays C and E release in turn. Ringing, connection and release. If the wanted line is free, relay H operates [earth, b<4>, e<1>, c', H (1), private wiper to battery] and locks up over its winding 2. Ringing current is fed over a circuit F (2), e<3>, b wire, back by a wire, and f<2>, and a ringing signal is sent back over the wire R S. When the subscriber answers, relay F operates, opening a short-circuit round its winding 1, which energizes and the called line is extended to relay D which operates its contacts d', d<2> to give the answering supervisory signal. When the calling subscriber hangs up, relays A, B. H, E, D relapse in turn and the release magnet M M is energized. Contact m m opens to prevent seizure of the switch before it returns to normal. If the called subscriber hangs up first, relay D relapses and a warning lamp C S H is lighted. Busy signal and release. If the line is busy, relay F operates [battery, F (1), e<4>, w<1>, b<3>, earth] disconnects the ringing circuits, and connects busy tone over wire B B to the a wire. When the battery is on the wire B B, relay D (2) operates and both the a and b wires are battery connected. Relay A relapses, but relay B is held over a circuit d<3>, f<6>, b', h<1>. When earth is connected to the wire B B, D relapses, and A re-energizes. The distant bridged relay is therefore flashed together with the lamp C S H, and, if an operator is calling, a supervisory lamp. Instead of using the test relay for disabling the reversing contacts of the backbridge relay, a discriminating relay may be used with contacts in the impulse relay circuit. According to the Provisional Specification, such a relay only operates when the wanted line is free; when busy condition is met, the earthconnected impulse relay coil is disconnected and batterv is connected to the a wire over a non- inductive resistance; modifications of the circuit shewn in Specification 233,288 are described in which a second winding on the relay C therein may be used as a discriminating relay.