Patent GB-394775-A (GB)
Title: Improvements relating to automatic telephone and like selective systems
IPC: H04M3/523
Filed: 1932-03-24
Abstract: 394,775. Automatic exchange systems. SIEMENS BROS. & CO., Ltd., Caxton House, Tothill Street, PATTERSON, W. G., 68, Eltham Road, Lee, both in London, and LONG, D. P., 3, Ingleby Way, Chislehurst, Kent. March 24, 1932, No. 8807. [Class 40 (iv).]. Chain-starting-circuit arrangements for finder switches for associating common control circuits with selectors are such that when one control circuit is taken into use the starting circuit is extended to the next in the chain after a definite time interval corresponding to the release period of a normally-energized sluggish relay, this period being sufficient for the finder under normal conditions to move over all its contacts. A second control circuit will thus always become available even if the first is faulty. The invention is described with reference to two systems, one of which is substantially identical with the satellite discriminator system described in Specification 394,772. In the other system, as shown in the Figure, the chain-controlling relay GP is normally energized in series with relay FX which is not energized. When the selector is seized, relay L operating over the calling loop completes circuits for starting relays ST in two common control circuits, one in each of two sub-groups. Relay ST closes the circuit for the finder latch-magnet FLM which in turn controls the motor magnets FM. As soon as the finder moves off normal, relay GP is short-circuited and remains so as long as either the finder or digit switch is off normal, and relay FX energizes to disconnect ST, the finder movement being continued owing to the closure of contacts on 1. When the selector is found, relay TA operates in series with relay K over wiper F1 and connects up TB. Relays K, TB, connect the incoming loop to the impulse relay A, a reversal of current being sent back over the loop to signal a register-controller if such is used. Relays B (i), C (i), operate, and impulses are repeated to magnet DSM. At the end of the digit, the latch-magnet LM of the selector is operated over wipers F6, DS4, and the selector hunts over the marked group under the control of relay T to the common control circuit. When an idle outlet is found, relay T operates over wiper DS2, one of the wipers F7 .. F11, and selector banks M, P, and connects up TT which completes a circuit for switching relay H and controls the transmission of a discriminating signal forward over the a-wire according to the setting on bank DS3. If all outlets are busy, the selector moves to the end of its bank where relay LC operates to connect up busy tone BS. Bank DS5 controls the operation of congestion meters OM on " live " groups and of a relay SL which energizes on " dead " groups to connect up NU tone. With the arrangement shown, if a finder searches the end of its bank without finding a calling line and the calling signal still persists, relay GP will be re-energized before it has fully released and the finder will hunt a second time. Arrangements may however be made whereby the circuit of GP cannot be again closed until a fresh starting signal is received so that after an unsuccessful hunt by one finder, a second one will be taken into use.