Patent GB-241522-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1925-06-18
Abstract: 241,522. Automatic Telephone Manufacturing Co., Ltd., (Assignees of Stehlik, R. F.). Oct. 17, 1924, [Convention date]. Automatic exchange systems.-Relates to improved circuit arrangements for selectors and connectors, and includes the following features- (1) the release relay is shunted at each impulse by the series relay, and is de-energized, when the calling subscriber hangs up, by prolonged shunting by the same relay; (2) the switches are guarded against seizure during release by the series relay (indirectly in the case of a selector); (3) at the connector the same series relay is energized in turn with each of the operating magnets and the release magnet; and (4) a, busy relay when energized short-circuits the series relay and so prevents the series relay from unlocking it in case the subscriber should send a further digit to move the connector on to an idle line. Establishment of connection. The line relay 21 of the selector S connects up the high-resistance release relay 22 over rotary magnet 29. Dialled impulses are repeated to vertical magnet 26, relay 22 being shunted at each impulse by the lowresistance series relay 23 and remaining operated. Stepping relay 24 energizes when off-normal contacts 31 are closed, so that at the end of the impulse train when series relay 23 falls back, rotary magnet 29 is connected up and interacts with stepping relay 24 in the usual way. Switching relay 25 energizes when an idle connector is found and extends the connection. The line relay 102 of the connector C connects up high-resistance release relay 103 over vertical magnet 111, to which impulses are then repeated, relay 103 being shunted at each impulse by low-resistance series relay 107 as in the case of the selector S. At the end of the train, relay 107 falls back and change-over relay 104 energizes, transferring the impulsing circuit to rotary magnet 112, series relay 107 being energized during the impulse train as before. If the wanted line is busy. busy relay 106 energizes over the test wiper before relay 107 falls back and subsequently locks, connecting up the usual busy tone, disconnecting switching relay 108 and short-circuiting relay 107 to prevent it from unlocking relay 106 should a further digit be sent. If the wanted line is idle, switching relav 108 energizes when series relay 107 falls back, and the circuit of release relay 103 over vertical magnet 111 is re-established. Ringing takes place, and ring cut-off relay 105 energizes upon reply of the called subscriber and completes the talking connection, back-bridge relay 101 being energized in the usual manner. Release. When the calling subscriber hangs up, line relay 102 falls back, connecting up relay 107, which shunts release relay 103 and disconnects the test wiper at contact 138. Release relay 103 relapses and removes ground from the test wire 46 to release the selector S. Relay 107 falls back and re-connects the test wire 46 to the test wiper to guard against seizure of the connector, which is held by back-bridge relay 101 until the called subscriber hangs up. When relay 101 is released, release magnet 109 operates in series with relay 107 to restore the wipers, and switching relay 108 is disconnected, so that the test wire 46 is grounded over contacts 139, 142. At the selector S, switching relay 25 upon relapse connects up release magnet 27 in series with relay 23, and the latter causes stepping relay 24 to energize and ground the test wire 17 at contact 36. Two modified selectors are described. In one modification, the series relay 23 is short-circuited upon energization of the line relay 21 so it need not be made slow-acting by construction, and the test wiper is connected up independently of the series relay, being grounded on energization thereof. In the other modification, the release relay 22 is energized initially over the vertical magnet 26 instead of the rotary magnet 29.