GB427441A - Improvements in or relating to telephone systems - Google Patents

Abstract

427,441. Automatic exchange systems. GENERAL ELECTRIC CO., Ltd., Magnet House, Kingsway, London, and CARPENTER, 0.1., c /o General Electric Co., Stoke, Coventry. Jan. 15, 1934, No. 1395. [Class 40 (iv)] In a small private branch exchange of the kind described in Specification 426,224, in which the dialling of the digit 0 returns a signal from the connector to call the operator and effect release of the finder-connector link, the subscribers' line circuits comprise line and cut-off relays L, K of ordinary type, both relays being operative during conversation, and the signal from the connector brings about operation of K and release of L. When a call is initiated, L energizes over its upper winding in series with a start relay, while when the calling line is found, earth on lead 18 operates K and holds L over its lower winding. When the line is seized by a local connector or by a switch associated with a junction, earth on lead 7 or 12 operates first L and then K. This condition also obtains when the operator seizes the line by throwing key SK. If the digit 0 is dialled, earth is applied to lead 17 as well to lead 18, so that L is shunted out while K locks over the calling line, ringing tone is connected to the line, the lamp LA lights and earth is applied to lead 18 to short-circuit the holding relay in the finder-connector link. If the subscriber initiates an outgoing call by dialling 9, a switch associated with an idle junction hunts for the line, which is marked by battery on lead 17, and when found earth is extended from lead 12 to lead 18 to release the local switches.