Patent GB-258306-A (GB)
Title: Improvements relating to telephone systems
IPC: H04Q3/58
Filed: 1925-04-21
Abstract: 258,306. Siemens Bros. & Co., Ltd., and Patterson, W. G. April 21, 1925. Automatic exchange systems ; metering.- In a system in which a junction is selected by a subscriber's line switch which is held from the originating end of the junction, means are provided whereby the junction may be freed by a circuit change at the incoming end although the subscriber's line is still in the calling condition. The invention is particularly suitable for unattended satellite exchanges in which it is desirable to release a main exchange junction when a satellite subscriber's line develops a permanent loop fault or when a subscriber unduly delays dialling. The subscriber's line switch should be of the kind described in Specification 241.655 in which after such release if the line is still in the calling condition it moves to a last position without picking up a further free junction. First arrangements, Fig. 2. A junction a, b to the main exchange is selected by a satellite exchange subscriber's line switch identical with that described with reference to Fig. 4 of Specification 241,655. The switch is of the kind in which the test relay is released to restore the line switch when battery is removed from the test wire but in advancing to normal does not pick up a further free junction as its test-in circuit is held open by a latched contact on the test relay which is only closed in the last position of the switch. When the junction is taken into use, the impulse relay A of a repeater at the outgoing end closes the impulsing circuit over relay RA, the b wire, and the impulse relay AA of the incoming selector. Relay RA energizes the usual slow-release relay V which in turn energizes relay E which marks the junction busy. Relay RA closes a circuit for relay VV, and when next a depression on a continuously rotating cam 10 comes under spring 12, relay SA is energized over springs 11, 12, offnormal contact k1 and winding 1, and locks over winding 2. If no dialling impulses are received before cam 10 makes a full revolution and closes contacts 12, 13, relay ZA energizes in series with winding 3 of relay SA and opens the impulse circuit, causing the relapse of relays RA, V. Relay V opens the circuit of the test relay of the line switch, which moves to its last position in which it remains sending back busy tone as long as the subscriber's line is looped, as described in Specification 241,655. Relay 1 relapses after an interval and marks the repeater selectable. The usual delayed metering arrangement and circuits for transferring release control to a manual operator, are provided at the outgoing repeater. Second arrangement, Fig. 4. In this loop impulsing is employed over the junction, the incoming selector is of the kind in which the line relay is disconnected when it has selected an idle trunk, and the satellite exchange line switch is identical with that described with reference to Fig. 1 of Specification 241,655. When the junction a, b is seized, the line relay A of the outgoing repeater closes a loop to the line relav AA of the incoming selector over relav E and winding 2 of relay D. Relay E energizes slowrelease relay B which earths the test wire c and energizes winding 1 of a differential relay D which remains inert. During impulsing, relay C short-circuits relay E but relay B is held over contacts c1. When the called subscriber answers relay D responds due to a current reversal through its winding 2, and earths wire m to effect metering. The selector line relay AA lights an alarm lamp PL which normally is extinguished when the incoming selector seizes an idle trunk but which in the case of a permanent loop continues to glow. The main exchange attendant thereupon presses a key K causing the release of relays A, E, B. Relay B disconnects the test wire c to the line switch which moves to its last position and remains there giving a busy signal until the fault is cleared, as described in Specification 241,655. Automatic release means similar to those, described with reference to Fig. 2 may be provided at the incoming selector in place of the key K. Third arrangement, Fig. 5. The delayed metering relays S, Z, at the outgoing repeater are also used for releasing the junction in the event of delayed dialling or a permanent loop. When a line switch, as in the first arrangement, seizes the junction, relays A, V, E energize, and on the first impulse relay L responds and locks up : impulses are repeated at contact a2. On the reply of the called party, relay Y closes a circuit for winding 1 of relay S over springs 15, 16 and relay S locks over winding 2. After a suitable interval cam 14 closes springs 16, 17, relay Z is operated, locks up and meters the call. If no impulses are received, relay L does not respond, relay S energizes over winding 1 and springs 19, 20 of a cam 18. locks up over winding 2, and if when after an interval springs 20, 21 close no impulses have still been received, relay Z energizes, locks up, and disconnects the test wire to cause the line switch to release the junction as in the first arrangement. Since the relay S may be energized over contact l2 if the springs 19, 20 are closed before impulsing, a contact y3 is included in the circuit of the lefthand winding of relay Z to prevent this relay from energizing and metering, if the subscriber dials when the springs 16, 17 are in contact. During metering the circuit of relay Z includes the right-hand winding of relay Y to prevent the called subscriber from interferring with metering by dialling or moving his receiver hook. Fourth arrangement, Fig. 6. This describes the application of the invention to a satellite exchange system of the kind described in Specification 222,246 in which upon an idle outgoing repeater being picked up by a line switch an associated switch DF searches for an idle discriminator, the finding of which starts another associated switch JF in search of a main office trunk. The discriminator responds to dialled impulses and if the call is a local one disconnects the main office trunk. The normal operation is the same as that described with reference to Fig. 1 of the last-mentioned Specification with the exception that the impulse circuit to the incoming selector at the main exchange includes a slow-release relay RA, which opens the circuit of an additional slow-to-operate relay J before it can pull up on the response of relay TJ. On the first relapse of the line relay A, relay B energizes, locks up, and opens a further point in the circuit of relay J. If, due to a fault or other cause, no impulses are received at the repeater, when the b wire is opened manually or by a time alarm at the main exchange, the relay RA de-energizes, and since the relay B has not responded, the relay J energizes over a circuit ra1 tj5, b5, locks up, and disconnects battery from the test wire c to cause the line switch to advance to its last position as described in the first arrangement. Relays E, V, TJ, TD, J then relapse in turn and the repeater is a gain rendered selectable.