Patent GB-191229358-A (GB)
Title: Improvements in or relating to Telephone Systems.
Filed: 1912-12-20
Granted: 1913-12-22
Abstract: 29,358. Automatic Telephone Manufacturing Co., [Automatic Electric Co.]. Dec. 20. Automatic exchange systems. - Each subscriber's line terminates at the exchange in a line switch having wipers which rest normally on the terminals of a trunk leading to a disengaged first selector. When a subscriber calls, his line is connected to the pre-selected trunk by the movement of a side-switch associated with his line switch, and at the same time circuits are closed through the propelling-magnets of all the idle line switches of the same group to advance them to the terminals of the next disengaged trunk. The arrangement involves a master switch which marks all but one of the trunks non-selectable at a given moment. The invention is described in connexion with a system in which selective switches of Strowger type are controlled by impulses which pass from ground at the sub-station over one or other of the subscriber's line wires. Subscriber's impulse transmitter. This is the same as in Specification 1420/10. Line switch C and group switch D. A construction of line switch C with its associated two-position side switch K is shown in Fig. 3. It comprises a propelling magnet 45, magnets 39 and 55 which respectively operate and restore the side-switch, a cut-off relay 67, and release relays 68, 69. The switch D, Fig. 1, which is common to a group of line switches, comprises a propelling-magnet 74 and wipers 80, 81. The wiper 81, which has a slight angular advance on the wiper 80, serves to disconnect its bank terminals from a set of grounded springs, all the terminals being grounded except that on which the wiper rests. The function of the switch D is to maintain a non-selectable potential on the test-terminals of all the trunks except the one on which it is resting, thus rendering it impossible for a disengaged line switch to rest on any other disengaged trunk. The operations when a subscriber A, Fig. 1, calls a subscriber A', Fig. 2, are as follows. The preliminary rotary impulse, sent when the subscriber first operates his dial, passes over the line 32 to the magnet 39, which trips the sideswitch to its second position, connecting the line 31, 32 through the wipers 49, 50 to the preselected trunk 160, 161. At the same time the subscriber's line is marked busy by the grounding of his test-wire over the side-switch wiper 43, and a circuit is closed through the sideswitch wiper 44 and test-relay 51 to the propelling-magnets of the group switch D and of all the disengaged line switches, such as L, belonging to the same group as the switch C. The switches D, L, &c. therefore move to the terminals of the next trunk, and if that is engaged they continue moving until an idle trunk is reached. First selector E. The vertical impulses representing the first digit are repeated by the relay 108 to the vertical magnet 96, and the succeeding rotary impulse is repeated by the relay 109 to the private magnet 99, which trips the sideswitch to its second position, in which a circuit is closed through the self-interrupting rotary magnet 97. The process of hunting for an idle trunk then proceeds in the usual manner under the control of the magnets 97, 99, the sideswitch tripping to its third position when the wiper 121 finds an ungrounded terminal. Connector F. In response to the impulses representing the last two digits, the vertical and rotary magnets 130, 131 and the private magnet 133 operate in the usual manner to select the terminals of the wanted line and to bring the side-switch to its third position. The cut-off relay 178 of the called subscriber's lineswitch C' is energized over the test-wiper 127. Supply of ringing-current. When the subscriber A presses his ringing-key 37, so as to ground the line-wire 31, the relay 128 energizes the ringing-relay 132. Release. When the calling subscriber hangs up his instrument, both sides of his line are momentarily grounded at the springs 7, 8, 9, and the consequent simultaneous energization of the connector line-relays 128, 129 closes a circuit through the connector release magnet 134 and the selector release relay 115. At the same time the simultaneous energization of the lineswitch relays 68, 69 energizes the magnet 55, which restores the side-switch to its first position and locks itself up over the wire 32, disconnecting the magnet 39 until the groundconnexion at the sub-station is broken. The propelling - magnet 45 is energized over the wipers 44, 51 and operates to bring the lineswitch C to the terminals of the same trunk as the group switch D. If the called subscriber should be the first to disconnect himself, the connector is released at once by the energization of the relays 142, 143.