Patent GB-233859-A (GB)
Title: Improvements relating to automatic telephone systems
IPC: H04Q3/58
Filed: 1924-04-17
Abstract: 233,859. Siemens Bros. & Co., Ltd., and Patterson, W. G. April 17, 1924. Automatic and semi-automatic exchange systems; metering.-A repeater at the outgoing end of a two-wire trunk provides an initial holding circuit which is opened after an interval and replaced by a permanent holding circuit controlled by a relay operated by a transient current fed back over the trunk. If the trunk or selector at the incoming end thereof is faulty, this relay fails to operate and the trunk is released, and the switch which has seized it performs a further hunting movement. Several arrangements are described, in some of which weak current is fed back over the trunk to place release under the control of a called operator, and strong current is fed back to effect metering. First arrangement, Figs. 2 and 4, in which the trunk terminates in a selector and is seized by a line switch, loop impulsing being employed. At the selector, Fig. 4, the trunk a-wire is connected to battery over the wire 10, the connection over contacts k3, y2, v4 being removed. When line relay AR of the repeater, Fig. 2, energizes, relay YR energizes over the trunk in series with line relay A and connects up relay JT, which connects further battery to the incoming test circuit at contact jt2. Release relay VR energizes, disconnecting the original test circuit at contact vr2, and locking relay JT. In the case of a fault, relay YR does not operate, and upon energization of relay VR the trunk is released and the line switch performs a further hunting movement. Second arrangement, Figs. 3, 4, employing leg impulsing and including delayed metering arrangements. The connection 10 in the selector, Fig. 4, is now removed. Line relay AR and relay C energize at the repeater, Fig. 2, so that relay B energizes over the trunk b-wire in series with line relay A. Release relay V at the selector energizes and connects battery to the a-wire to energize relay YR, so that relay JT also operates. Meanwhile, release relay VR energizes, locks relay JT and connects up sluggish relay E, which energizes over the incoming test circuit and renders it dependent on relays AR, VR at contacts ar3, vr1, and releases relay C, but relay VR is now held by contact jt2 of relay JT. In the case of a fault, relays YR, JT do not operate and the trunk is released. If the trunk is short-circuited when not in use, relays B, A energize through the short-circuit, the former opening the test circuit at contact b1 and the latter connecting up relays V, PL to close an alarm circuit. Earth is connected intermittently to wires 20, 30 to control metering. Relay YR re-operates when answering relay Y at the selector energizes and connects battery to relay S, which energizes over wire 20, locks and connects wire 30 to relay Z, so that the latter energizes after an interval and locks. Increased metering current is connected to the test circuit at contacts s1, z1. Relay YR is not energized long enough during, trunk testing to effect metering. Third arrangement, Figs. 5, 6, in which the trunk is held by a weak current fed back thereover, and this operation may be repeated to place release under the control of a called operator. Line relay AR of the repeater, Fig. 5, energizes initially over the test circuit, connecting up release relay VR which connects sluggish relay DR to the test circuit. Relay DR disconnects relay AR from the test circuit. Meanwhile relay AR closes a circuit for line relav A at the selector, Fig. 6, over the b-wire, so that release relay V energizes and connects weak current through relay HA over the a-wire to relays HR, YR. Only relay HR energizes, connecting up relay JT which locks and completes the. loop circuit for line relay AR to prevent release of the trunk. If the trunk is short-circuited, relay YR energizes as well as relay HR and prevents the energization of relay JT. Answering relay Y connects direct battery over contact y3 to the a-wire, so that relays HR, YR both operate to effect metering. In the case of a call to an operator's position, weak current fed back over the a-wire from the cord circuit operates relay H but not relay Y, so that weak current is repeated back at contact h1 to energize relay HR, while relay HA closes a holding circuit for release relay V at the selector. Fourth arrangement, Figs. 7, 8, 10, in which the trunk leads directly to an operator's position and is seized by a selector. Line relay A of the selector, Fig. 7, energizes first over the test circuit and then over the subscriber's loop, and release and dialling relays V, D operate. Impulses are repeated at back contact a1 and relay D is held at back contact a2, and releases to connect up the rotary magnet. Relay L energizes at the first impulse, locks and connects up test relay TS which energizes in the usual way when an idle trunk is found. Relay AA at the repeater, Fig. 8, energizes over the test circuit, and sluggish relays VA, DA operate in turn, the latter opening the circuit of relay AA so that the test circuit is controlled by release relay VA at contact va1. Relay DA also connects relays JTA, JTB to the trunk, so that the former is energized by weak current thereover, locks and closes a holding circuit for relay AA to prevent release of the trunk. If the b-wire is earthed, relav JTB also operates, locks, releases relay DA and opens the holding circuit of relay AA, while in the case of other faults, relay JTA does not operate. Relay LR energizes at the operator's position and lights a calling lamp. Fifth arrangement, Fig. 7, 9, 10, in which weak current is fed back from an operator's cord circuit to place release under her control. Relay LR at the operator's position, Fig. 10, energizes over the trunk b-wire and feeds back weak current over contact lr2 and the a-wire to energize relay JTA to close a holding circuit for relay AA at the repeater, Fig. 9, as in the last arrangement. When the operator plugs in, relay N energizes and connects weak current to the a-wire to operate relay H at the selector, Fig. 7, but not relay Y to lock release relay V.