Patent GB-191219254-A (GB)
Title: Improvements in or relating to Telephone Systems.
Filed: 1912-08-22
Granted: 1913-08-22
Abstract: 19,254. Automatic Telephone Manufacturing Co., [Automatic Electric Co.]. Aug. 22. Automatic exchange systems.-Relates to inter-exchange trunking systems in which line switches are arranged between group selectors and the trunks to distant exchanges, in order to make these trunks more widely available. According to the present invention, the group selector is prevented from obtaining access to an idle line switch, if all the trunks leading therefrom are in use. The bank contacts in each level of the group selectors C, Fig. 3, lead to line switches D having access to different groups of trunks H. When all the outgoing trunks of the master-switch are in use, its hunting-operation is arrested by opening the circuit of its motor magnet. The invention is described as applied to a three-wire system in which each line terminates in a first selector C having access to non - numerical trunking- switches D, similar to the line-switches described in Specification 26,301/06, leading to repeaters F controlling the second selectors H and connectors I at the distant exchange. The subscriber's impulse transmitter is similar to that described in Specification 1420/10. The operations when a subscriber A calls a subscriber A<1> at a distant exchange are as follows:- Group selector. The first set of selecting- impulses is repeated by the vertical relay 45 to the vertical magnet 36, and the succeeding rotary impulse is repeated by the rotary relay 46 to the private magnet 38, which moves the side-switch into second position, thereby energizing the rotary magnet 37. As soon as an idle line-switch D is found, the side-switch moves to its third position in the usual way, extending the calling line to the line-switch, and earthing its test lead over the low-wound back-release relay 220. Trunking line-switch. The plunger magnet 48 is thus energized by current passing from the grounded test lead through the magnet 48, contacts 58, 57, 107, 109, and coil 71 to battery, thus extending the calling line to the repeater F of an idle trunk. In its attracted position, the plunger arm 47 connects the magnet 48 through a resistance 111 direct to the battery lead. The closing of contact 53, 54 energizes the relay 70, which causes the master-switch E to rotate in the manner described in Specification 1418/10 until it finds an idle trunk. The closure of contact 53, 54 also energizes a relay 67 individual to the selected trunk. Corresponding relays 68, 69 are provided for each trunk available from the line-switch, so that when all the trunks are busy, a circuit is closed over the contacts 119, 117 of these relays for a relay 72, which (1) opens at contact 116 the circuit of the relay 70 so as to prevent continuous movement of the master-switch while all the trunks are in use, (2) closes the circuit of a lamp 73, (3) disconnects at contact 107 the magnets 48 of all the line-switches controlled by this master-switch, and (4) directly grounds these magnets so as to make these line-switches test busy to first selectors C. Repeater and second selector. The second set of selecting-impulses is repeated by the relay 74, Fig. 1, to the relay 138, Fig. 2, and thence to the vertical magnet of the second selector H. The second rotary impulse is similarly repeated by the relay 75, Fig. 1, to the relay 148, Fig. 2, and private magnet 151. The second selector operates in the same way as the first selector. The relay 76, which is operated by both the vertical and rotary impulses, serves to disconnect the relay 77 from across the trunk 132, 146, during the transmission of impulses. Connector. The third set of impulses is similarly repeated by the relay 74, Fig. 1, to the relay 89, Fig. 2, and thence to the vertical magnet 81. The succeeding rotary impulse is repeated by the relay 75, Fig. 1, to the relay 90, Fig. 2, and thereby to the private magnet 83, which moves the side-switch to its second position so that the final set of impulses is repeated to the rotary magnet 82. Busy test and busy release. The final rotary impulse is repeated to the private magnet 83 as before, and if the called line is busy, and therefore has its test lead earthed, the private magnet energizes the release magnet 88 over a circuit which passes from the battery lead 139 through the contacts 167, 168 of the relay 93 (energized by the rotary impulse), magnet 88, contact 212, side-switch arm 86, to the earthed test lead. The connector is thus released, and when the calling subscriber depresses his ring- ing-button, the connector is raised one or more steps and connects the busy generator M to the calling line over the side-switch arm 84 in its first position. The rest of the apparatus is released when the calling subscriber replaces his receiver. Supply of ringing-current. If the required line is idle, the side-switch passes into its third position, in which the cut-off relay 162 of the called subscriber's selector is energized over the test lead and arm 86. The depression of the calling button 30, Fig. 1, earths the vertical lead, thus energizing the relays 74, Fig. 1, and 93, Fig. 2, and the latter completes the circuit of the ringing-relay 91, which connects the generator R across the called line. Reply and supply of microphone current. When the called subscriber replies, he is supplied with microphone current through the backbridge relay 92, which energizes and completes a circuit for the relay 77, Fig. 1, of the repeater, through the opposing-coils of the relay 93. The relay 77 reverses the connexions of the lower winding of the differential relay 76, through which the calling subscriber is then supplied with microphone current. Release. When the calling subscriber replaces his receiver, his vertical and rotary leads are grounded simultaneously, thus energizing the relays 74, 75, 76, which in turn energize the relays 89, 90, 93 of the connector. The release magnet 88 is thus energized in series with the release relay 198 of the second selector, thus energizing its release magnet 203. The simultaneous excitation of relays 74, 75, 76 also energizes the release relay 220 of the first selector, which excites its release magnet 43. As soon as the earth circuit is broken at the sub-station, the release relays and magnets are all de-energized, thus breaking down the connexion.