Patent GB-191406659-A (GB)
Title: Improvements in or relating to Telephone Systems.
Inventor: MARTIN TALBOT GRANT
Filed: 1914-03-16
Granted: 1915-03-16
Abstract: 6659. Martin, T. G. March 17, 1913, [Convention date]. Semi-automatic exchange systems.-Relates to means for giving a busy signal to the calling subscriber and to the operator when an attempt is made to connect to a busy line, in systems of the kind in which a connexion is completed through a cord-circuit and a connector. The supervisory relay in the cord-circuit is arranged to energize in series with the connector line relay, and means associated with the connector alternately applies a busy signal current to the calling line, and short-circuits the supervisory relay to give a busy signal to the operator. The invention is shown applied to a system in which a calling subscriber T on a district office is connected by a line-switch C to an idle trunk terminating at the main exchange at a manual jack J. The operator completes the connexion to another district office subscriber T' by means of the cord-circuit O and connector E. Connexion of calling line to jack J. When the subscriber T removes his receiver, the line relay 19 energizes the pull-down winding 51 of the line-switch C, thus extending the line to a relay 57, which closes a circuit through an impedance 67 for the relays 64, 65, thus lighting the call lamp 21. The relay 57 also earths the winding 51, so as to maintain this energized when the line relay 19 is disconnected by the cut-off relay 20, which is energized over terminals 15, 16 and ground G<4>. The line and cut-off relays are mechanically separate from the line-switch, thus facilitating the conversion of a manual to a full automatic system. Operation of cord-circuit. On the insertion of a plug P, a relay 27 is energized in series with the relays 65, 69. The relay 69 disconnects relay 64, thus extinguishing the lamp 21. At the same time, a relay 26 is energized over the impedance 67 and prevents the lighting of the lamp 24. After ascertaining the number of the wanted line, the operator inserts the plug P<1> in jack J<3>, thereby establishing circuits for a relay 29 over a resistance 73, and for the connector line relay 77 over a relay 28, which opens the circuit of the supervisory lamp 25. Connector. The operator then moves her switch K<2> to connect the impulse-sender 30 in circuit with the line relay 77, this circuit including one side of the connexion only. The relay 77 energizes a slow-release relay 79, which energizes a second slow-release relay 80. The tens and units selecting-impulses are repeated by the relay 77 over contacts 81, 82, and private-magnet relay 83 to the vertical and rotary magnets 34, 35 in the usual way. Busy test and signalling arrangements. If the wanted line is busy, the private magnet 40 remains energized over contact 93, relay 45, contact 92 and grounded test contact 140, thus locking the side-switch in its second position. The relay 45 locks up over ground G<14>, and connects a busy generator L over interrupter 46 and arm 36 to the calling line. During alternate intervals, an interrupter 47 directly earths the tip side of the trunk, thus short-circuiting the relay 28 and flashing the supervisory lamp 25. Ringing-current. If the wanted line is idle, the operator rings the subscriber in the usual way by depressing her key K<1>. Release. When the calling subscriber hangs up, the relay 57 opens the circuit of the relay 26, thus lighting the lamp 24, but the holding- circuit of the line-switch is maintained over a contact of relay 65. When the called subscriber hangs up, the relay 28 is de-energized and lights the lamp 25. The removal of the answering-plug disconnects the relay 65, which opens the holding-circuit of the line-switch C, and the removal of the calling-plug opens the circuit of a relay 89, which disconnects the relay 79, and this in turn de-energizes the relay 80, which closes the circuit of the release magnet 41.