Patent GB-230214-A (GB)
Title: Improved circuit arrangements for automatic telephone exchange systems
IPC: H04Q3/00
Filed: 1924-01-09
Abstract: 230,214. Siemens Bros. & Co., Ltd., and Christian, D. A. Jan. 9, 1924. Automatic and semi-automatic exchange systems.-In a system in which impulses are transmitted over circuits including earth returns, in order to avoid faulty operation due to any difference of earth potential, for example, at the two ends of an interexchange trunk, the impulses are transmitted over both speaking conductors but with the currents in opposite directions, so that any increase in current in one winding of the impulse relay is balanced by a corresponding decrease in the other winding. The impulse contacts in that one of the speaking conductors, which serves for the transmission of supervisory signals, may be short-circuited when no impulses are passing so that, when a connection is extended to a manual position, the release of the connection may be entirely under the control of the manual operator and the hanging up of the calling-subscriber's receiver will not break the supervisory circuit. The invention is described with reference to a system empoying an outgoing group selector, Fig. 1, having access over a two-wire interexchange trunk to an incoming group selector, Fig. 2, from which the connection may be extended to a manual position, Fig. 3, or over succeeding switches to an automatic subscriber. Delayed metering arrangements of the kind described in Specification 200,928 are employed at the outgoing selector, Fig. 1, but a modified arrangement is referred to in which metering takes place as soon as the called subscriber replies, the circuit arrangements being such that, although the answering supervisory relay is intermittently energized during impulsing, the metering circuit is held open at this time at a front contact of the change-over relay, which is energized during each digit. In a further modification, for use in systems in which the battery and earth connections to the speaking conductors are reversed on the reply of the called subscriber, the outgoing end of the inter-exchange trunk is provided with a repeater comprising an impulse relay including in its circuit contacts of a reversing relay, the circuit of the latter relay including front contacts of the answering supervisory relay but also back contacts of a relay which is energized during impulsing, so that the intermittent operation of the supervisory relay during impulsing does not operate the reversing relay. At the incoming end of the trunk, one winding of the impulse-receiving relay is directly connected to one speaking conductor whilst the other winding is connected to the other conductor, either over front contacts of a bridge polarized answering relay or over front contacts of a relay energized during impulsing. Outgoing selector, Fig. 1. The operation of relay A energizes release relay V and completes a circuit over contacts v3, l3, k3, v1 for changeover relay D, which connects up dialling tone DS. The first impulse is repeated to the vertical magnet VM over contact a1, the off-normal contacts operate, and relay D is left dependent upon an intermittently-closed locking circuit a2, d1, k3, v1. The, closure of front contact a2 at the end of the first impulse completes a circuit v3, y2, a2, d1, v1 for relay L which locks up independent of relay D. At the end of the digit, relay D relapses and completes an interrupter circuit for the rotary magnet RM which rotates the wipers until an idle trunk is found, when relay T energizes over winding 1, locks up over winding 2, and grounds the test wiper. The trunk may be a twoway one, in which case a cut-off relay connected to the test terminal disconnects the incoming selector from the trunk. At the beginning of each succeeding train of impulses, relay D energizes over hack contact a2 and front contact l1 and remains energized throughout the train, so that the opening of the normal short-circuit around the contacts a<4> permits the impulses to be repeated at both contacts a3 and a4 and thence over both speaking conductors. Incoming selector, Fig. 2. When the trunk is seized, relay AA energizes over winding 1 and the b-wire, and relay VV operates and completes a circuit for relay DD. Relays DD, LL are similar to relays D, L, respectively, Fig. 1. The operation of the vertical magnet in response to the first impulse repeated over the b-wire closes contact kk1, thereby connecting up winding 2 of relay AA to battery so that subsequent impulses pass over both a- and b-wires, the currents, however, being in opposite directions. Succeeding trains of impulses may be repeated to further selectors at a third exchange over both speaking wires in the manner already described, or to local selectors over one wire only. Supervision and metering.. When the called subscriber replies, relays YY, HH energize, releasing relay LL and connecting direct battery over winding 2 of relay AA in series with which relays Y, H operate, and their continued operation, as distinct from the intermittent operation during impulsing, releases relay L and connects up winding 1 of relay S. Relays S, Z then operate in the manner described in Specification 200,928 to transmit, after an interval, a metering impulse over contacts z1, s1. Release; signalling delay of calling subscriber in hanging up his receiver. When the calling subscriber hangs up, the release of relays A, V and the unlocking of relay T complete a circuit for release magnet M. The release of relay AA and the de-energization of relays YY, HH due to the hanging up by the called subscriber, release relay VV which restores the incoming selector and succeeding switches. If the called subscriber hangs .up first, lamps PLL, Fig. 2, and PL, Fig. 1, are lit until the calling subscriber also hangs up. Call to manual position. Fig. 3. When relay TT, Fig. 2, switches through, relay N operates to light the call lamp 12 and to connect. up a camoperated spring 14 which alternately applies ring- ing current and direct battery to the a-wire. The time of application of battery is sufficient for relay YY, Y to release relay LL, L, but not for metering to take place. When the operator plugs in, relay CO cuts off relay N and the circuit of the a-wire now includes a resistance R so that relays HH, H only energize and close holding circuits for relays VV, V independent of the calling subscriber, no metering taking place.