Patent GB-191210376-A (GB)
Title: Improvements in or relating to Telephone Systems.
Inventor: MARTIN TALBOT GRANT
Filed: 1912-05-01
Granted: 1913-05-01
Abstract: 10,376. Martin, T. G. May 2, 1911, [Convention date]. Automatic exchange systems.-Relates to the circuit arrangements of a two - wire group selector of the kind in which there is no sideswitch, the switching of the talking-conductors to the selector wipers being effected by a lineswitching relay. Release is prevented, during the setting of the selector, by the customary slow-acting relay, but during the conversation it is under the control of the line-switching relay, which is of a quick-acting type. This obviates the usual slight delay between the removal of the busy potential from the test terminals of a selector and its release. The connector is of the side-switch type. Line switch and master switch. These are of the type described in Specification 26,301/06 and operate as in Specification 1419/10 to connect a calling subscriber immediately to an idle first selector E. First selector. The line relay 77, energized over the calling line, closes the circuit of the slow-release relay 82, which connects ground G<4> to the holding-winding 44 of the line-switch C and to the calling subscriber's test-terminals 174. The current-interruptions representing the first digit are repeated by the relay 77, over contacts 112, 122, 130, to a slow-release relay 83 in series with the vertical magnet 70, which steps up the wipers 67, 68, 69 to the required level. The relay 83 energizes a test-relay 133, which locks itself up in a circuit including a contact 72 controlled by the rotary magnet 71. At the conclusion of the series of impulses, the relay 83 relapses and completes a circuit for the rotary magnet 71 over the contacts 73, 136, 135, 72, 113. The magnet 71 moves the wipers on to the first set of terminals and at the end of its stroke breaks its own circuit and that of the test-relay 133 by opening the contacts 72, 73. If the first trunk in the selected level is already busy, its test-terminals will be grounded, and the relay 133 will be kept energized over the test wiper 69 and will maintain the self-interrupting circuit of the rotary magnet. When an idle trunk is reached, the relay 133 becomes de-energized and cuts out the rotary magnet 71, at the same time closing a circuit for the lineswitching relay 76 through contacts 113, 72, 137 and the off-normal contact 79. The relay 76 disconnects the line-relay 77 and extends the connexion over the wipers 67, 68 to the second selector F, Fig. 2. Before the relay 82 has time to de-energize, a holding-circuit for the relay 76 and line-switch C is established over the test-wiper 69, which is immediately connected to ground G<9>, Fig. 2, by the energization of the relays 140, 143. Second selector. The second selector F, Fig. 2, operates in the same manner as the first selector to extend the connexions to an idle connector H. A holding-circuit for the relays 149, 76 and the line-switch C is closed from ground G<10> over contacts of the connector relays 147, 148, which are energized immediately the connector is seized. Connector. The current-interruptions representing the third and fourth digits operate the connector H, Fig. 2, in the usual manner to select the wanted line, and if the line is idle the side-switch moves to its third position to complete the connexion. Busy test and signal. If, however, the wanted subscriber is busy, the side-switch remains locked in its second position, the magnet 91 being kept energized, at the conclusion of the final series of impulses, by a circuit which includes the test-wiper 88, contact 178, the lower winding of the back-bridge relay 93, contact 185, the side-switch arm 169, and contact 195. The relay 93 energizes the relay 199, which locks the magnet 91 to ground at G<15> and connects the busy signal L to the calling-line over the condenser 204. Supply and control of ringing-current. This is the same as in Specification 1421/10. Release. When the calling subscriber hangs up his instrument the relays 147, 148 are deenergized and a circuit is closed for the connector release magnet 191. The disconnexion of ground G<10> from the test-wire 153 at the same time opens the holding-circuits of the selector relays 149, 76 and of the line-switch C. The de-energization of the relay 76 conipletes the circuit of the release-magnet 78, over the offnormal contact 80 and contacts 193, 122, 112, and the second selector is released in a corresponding manner.