Patent GB-397552-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04M5/10
Filed: 1932-02-26
Abstract: 397,552. Semi-automatic exchange systems. AUTOMATIC ELECTRIC CO., Ltd., Strowger Works, Liverpool. Feb. 26, 1932, No. 5844. Convention date, Feb. 26, 1931. [Class 40 (iv).] In a system including two-way junctions between a private branch exchange and a manual main exchange in which outgoing calls from the P.B.X, are set up automatically by the subscriber while incoming calls are set up manually by the attendant over a cord-circuit, the called subscriber in an incoming call may cause flashing of the supervisory lamp to recall the attendant by a single momentary interruption of the line. The junctions are of the general type disclosed in Specification 277,298, [Class 40 (iv), Telephones &c.], and are provided with a relay which is held locally in an outgoing call from the P.B.X. to prevent accidental release of the switches when the call is answered at the main exchange. Call from P.B.X. to main exchange. The calling subscriber obtains connection to a junction 130, 131 over the line switch LS and selector S. Line relays 101, 102 in the junction circuit energize in series with relay 133 at the main exchange, which lights lamp L3, while relay 102 connects up guard relay 103 and closes a holding circuit for itself and relay 101 through a resistance 111. When the operator plugs into the jack J3, relay 133 is disconnected by sleeve relay 132 and relay 104 energizes over wire 130 and completes the talking circuit.. Relay 102 is disconnected, while relay 101 remains operated in series with the feed relay of the cord circuit. Upon release by the calling subscriber, relays 101, 103 fall back and relay 106, which is of high resistance, energizes over the junction and causes relapse of the feed relay, thus giving the disconnect signal. A fresh circuit is closed for relay 104 which guards the junction until the operator clears. Call from main exchange to P.B.X. When the operator plugs into the jack J3, relay 106 energizes and connects up relay 104 which extends the talking circuit and guards the junction. Relay 105 operates in response to ringing current, locks and lights lamp L2. The P.B.X. attendant inserts the plug P1 of the cord C in the jack J2, closing a locking circuit for relay 104. Sleeve relay 30 energizes and relay 29 energizes over the loop in series with relay 101, which connects up relay 103 so that relay 106 falls back. The attendant connects her set to the junction by moving the key K to the right, and tests the wanted line by touching the sleeve of the jack J with the tip of the plug P. If the line is busy, she hears a click due to the operation of relay 75. Assuming the line is idle, on plugging in, sleeve relay 22 energizes in series with cut-off relay 4. Should the attendant plug into a busy line, relay 22 is short-circuited by busy ground. The key K is moved to the left and relay 23 energizes and applies ringing current through ring-trip relay 24, which operates on reply and completes the talking circuit. Feed relay 27 energizes, connects up relay 26, and gives a tone signal to the attendant if the key K has not been restored. To recall the attendant, the called subscriber depresses his switchhook momentarily or dials the digit one, whereupon the relapse of relay 27 energizes relay 25 which locks and connects up an interrupter to flash lamp L. The attendant enters the connection by moving the key K to the right, when relay 25 is disconnected. The main exchange operator may recall the attendant by applying ringing current, whereupon relay 28 energizes, locks, and flashes lamp L1. When the called subscriber hangs up, relay 27 falls back followed by relay 26, and the operation of relay 25 now causes lamp L to light steadily and lamp L1 to flash. Sleeve relay 22 relapses followed by relays 23, 24, and a resistance 81 is connected to wire 130 of the junction to release the feed relay at the main exchange, thus giving the disconnect signal. No ground is now connected to the sleeve circuit, so that the P.B.X. subscriber's line is available even if the attendant has not taken down the previous connection.