Patent GB-375384-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1931-03-23
Abstract: 375,384. Automatic exchange systems. AUTOMATIC ELECTRIC CO., Ltd., (formerly AUTOMATIC TELEPHONE MANUFACTURING CO., Ltd.), Strowger Works, TAYLOR, R., 30, Oulton Road, Wavertree, BELAS, F. T., 26, Arlescourt Road, and McCLEW, J. W., 27, Arlescourt Road, West Derby, all in Liverpool. March 23,1931, No. 8925. [Class 40 (iv).] In a bi-directional final selector, the dialling relay energizes prior to each movement of the selector and remains energized throughout the corresponding impulse train, and energizes a third time should the wanted line test busy. The invention is described as applied to ordinary final selectors and to final selectors provided with facilities for P.B.X. hunting and for breaking down a local call in favour of a toll call. The application described below incorporates both these features. The route of access to the selector determines whether it shall act as an ordinarv or as a toll final selector and also which of its two sets of wipers shall be employed. Local call. If the hundreds digit is even, the switch is seized over the second set of incoming wires, and relay WS energizes to switch in the lower set of wipers. Line and release relays 3A, 3B pull up, and an initial circuit is closed over contacts 3N:L. 3NR1 for dialling relay 3C, which holds in series with the vertical magnet 3VM during the vertical setting and then falls back. Change-over relay 3E energizes and closes a fresh circuit over contact 3NR1 for relay 3C, which now holds in series with the rotary magnet 3RM until the rotary setting is completed. Relays 3C, 3E then fall back in turn, and in the interim, provided the wanted line is idle, switching relay 3H energizes and locks over the test wiper. A metal rectifier 3RCT in the circuit guards against false operation of this relay by booster battery. Relay 3J pulls up, and ringing takes place in the usual manner, and ring-trip relay 3F and back-bridge relay 3D energize on the called party's reply. The current over the calling loop is reversed and booster battery is applied momentarily to the test wire pending the relapse of relay 3J. If the wanted line is busy, relay 3H does not energize and relay 3E on relapse connects up busy tone. Relay 3C re-operates without effect as shown, but it may control the busy tone circuit. Release. When the calling party hangs up, relay 3A falls back and relay 3E re-operates momentarily to remove ground from the test wire to release the preceding switches after relay 3B restores. When the called party hangs up, relay 3D falls back and disconnects relay 3H which closes the circuit of the release magnet 3ZM. P.B.X. hunting. An additional bank 1PBX is wiped over by two wipers of the trailing type which engage adjacent terminals simultaneously. If the first line of the P.B.X. group is busy, switching relay 3H is inoperative, and relay 1HS energizes and locks, closing a fresh circuit for the rotary magnet 3RM and relay 3C under the control of relay 3E which serves as a stepping relay. Relay 3C falls back at each step and completes the testing circuit through relay 3H, which operates when an idle line is reached and unlocks relay 1HS to stop the hunting. The last terminal of the bank 1PBX is unwired, so that relay 1HS is unlocked in this position and a busy signal is given if the last line of the group proves busy. For night service, one line of the group is connected through and is reached by dialling the corresponding number; since both wipers engage the bank 1PBX before relay 3C falls back, relay 1HS is short-circuited and a busy signal is given if the right service line is busy. Toll call. The switch is seized by a toll operator over the third or fourth set of incoming wires and relay 1CN energizes over the test wire and locks locally until the switch moves off-normal. Relay 3F energizes, short-circuiting the energizing winding of relay 1CN and disconnecting the ringing circuit. Assuming the wanted line is idle, switching relay 3H operates in the ordinary manner and connects back-bridge relay 3D to the line. To ring the subscriber, the operator actuates a control key which grounds one speaking wire to energize a differential relay 1DF in series with line relay 3A. Relay 3F releases by reason of a short-circuit and establishes the ringing circuit, and the call is completed in the usual manner. If however the wanted line is busy, busy tone is connected up on the relapse of relay 3E, and relay 3C re-operates. To break in, the operator actuates her control key to energize differential relay 1DF, whereupon relay 1CN pulls up over its middle winding, locks, and completes a speaking circuit to the wanted party. Relay 3C falls back. To break down a local connection, the control key is actuated again, whereupon relay 1BD energizes and locks, operating switching relay 3H in a local circuit and connecting direct ground to the test wiper to short-circuit the switching relay of the final selector or of the finder engaged in the local connection. In the former case, that is, when the wanted party is the called party in the local call, the relay corresponding to 3C re-operates and may extend busy tone to the calling party, as indicated in a previous paragraph. A toll connection cannot be broken down in this manner, since the switching relay of the final selector is locked locally without connection to the test wiper. If the wanted party has hung up, he may be rung again by a further actuation of the control key to release relay 3F.