Patent GB-191229352-A (GB)
Title: Improvements in or relating to Telephone Systems.
Filed: 1912-12-20
Granted: 1913-12-22
Abstract: 29,352. Automatic Telephone Manufacturing Co., [Automatic Electric Co.]. Dec. 20. Exchange systems.-In order to set free for further use the junction or trunk lines between different exchanges, or between different parts of the same exchange, at the earliest possible moment, they are restored to their normal condition when either subscriber replaces his receiver, and without any action of the operator. In the system described, line-switches of the kind described in Specification 26,301/06 are used to select idle trunks ahead of the calls, and also to connect incoming trunks to idle plug cords. The line-switches D, Fig. 2, which select the outgoing trunks 108, 109 are multipled to jacks J, Fig. 1, on the different operator's positions, and in order that an operator may not plug into a trunk leading to a line-switch already in use by another operator, switching- mechanism L, M, Fig. 1, is arranged to select idle trunks 89, 90 ahead of the calls and to control lamp signals b<1>, b<2> on the operator's positions in such a way that when an operator depresses a key 24, a lamp b<1> lights up to indicate the idle trunk which is to be used. The trunks 108, 109 selectable by the line-switch D, Fig. 2, terminate at the distant board or exchange in line switches F, Fig. 3, which connect them to idle plug cords C', Fig. 4, used to complete the connexion with the wanted line. If the subscriber P, Fig. 1, wishes to call subscriber P<1>, Fig. 4, the A-operator receives the call in the usual way, the supervisory relays 75, 76 being energized by the insertion of the answering-plug, and depresses the key 24 to find out which trunk is to be used. Means for indicating idle trunks to operator. The switching-mechanism R, which selects idle trunks ahead of the calls and indicates them to the operators, consists of a ratchet driving-disk 16 and two contact banks L, M in which pairs of wipers 12, 13 serve to connect continuous circular segments 18, 23 to one of the individual contacts a, a<1>. Each trunk 89, 90 is earthed through a relay 22, which serves to ground a contact a<1> corresponding to the particular trunk. When a trunk is taken into use, the grounding of its contact a<1> causes a relay 17 to energize the motor magnet 14, thus rotating the wipers 12, 13 until an idle trunk is found. The wipers 12 connect the battery B to the signal lamps b<1>, b<2>, the circuit of the selected lamp being completed by the depression of the key 24. While the switch R is in motion, warning lamps d<1>, d<2> are energized over the front contact of the relay 17. Operation of trunk-selecting switches D, Fig. 2, and F. Fig. 3. Having found the trunk to be used, the A-operator communicates with the distant operator over the order wires 87, 88, and, when the latter is free, inserts the calling plug in the selected jack. The relay 92, Fig. 1, is thus energized in series with the relays 98, 99, but the relay 99 is not energized at this stage owing to the resistance of the relay 98, which closes the circuit of the plunger magnet 25 of the line-switch D, thus extending the call to the pre-selected idle trunk 108, 109. The master switch E is then operated in the usual way. By the shifting of the spring 36, the plunger magnet is connected through a resistance 40 direct to the battery. The extension of the call to the trunk 108, 109 completes a circuit from the battery B, Fig. 1, through the relays 92, Fig. 1, 99, Fig. 2, 118, Fig. 3, 150, Fig. 2, and 151, Fig. 1. The resistance of the relay 118 prevents the energizing of the relays 150, 99, and 151, but the relay 118 excites the plunger magnet 121, Fig. 3, of the lineswitch F, thus extending the call to an idle plug cord C<1>, Fig. 4. The closure of contact 169 operates the masterswitch H in the usual way, and grounds the wire 134 thus energizing a relay 61, Fig. 4, and lighting the lamp 65. Connexion with called line, and supervisory signals. In response to the lamp 65, the B- operator inserts the calling plug p<2> in the jack of the wanted line, thus opening at contact 135 the circuit of the lamp 65 and closing at contact 171 a circuit for the lamp 63. The relay 62 is also energized in series with the cut-off relay 140, and completes the cord circuit. When the called subscriber replies, the relay 60 is energized, thus extinguishing the lamp 63, and completing the trunk circuit 130, 131 at contact 149. The current in the relays 99, 150, Fig. 2, and 151, Fig. 1, is thus increased sufficiently to energize them. The relay 151 disconnects the lamp 161 so that the A-operator knows that the called line has replied. The relay 150, Fig. 2, transfers the holding-ground of the plunger magnet 25 from G<10> to G<14>. Release of the connexion. If the calling subscriber hangs up first, the relay 75 is deenergized while the relay 76 remains energized, thereby short-circuiting the relay 92 over the armatures of relays 151, 75, 76. The relay 92 is consequently de-energized and opens the circuit of the relay 151, which destroys the short-circuit so that the relay 92 is again energized. When the relay 151 relapses, the circuit of the relay 150, Fig. 2, is opened, thus de-energizing the magnet 25 and releasing the line-switch D. The lamp 161 again lights up, informing the operator that the line-switch has released, and that the cord circuit may be withdrawn. The release of the line-switch D opens the circuit of the relay 118, Fig. 3, which releases the line-switch F, thus removing ground from the relay 61 so that the lamp 64 gives the clearing signal to the B-operator. If the called subscriber hangs up first, the relay 60, Fig. 4, de-energizes and opens at contact 149 the low-resistance circuit for the relay 150, Fig. 2, which brings about the release of both line-switches in the manner previously described.