Patent GB-191229360-A (GB)
Title: Improvements in or relating to Telephone Systems.
Filed: 1912-12-20
Granted: 1913-12-22
Abstract: 29,360. Automatic Telephone Manufacturing Co., [Automatic Electric Co.]. Dec. 20. Semi-automatic exchange systems.-In systems in which a calling subscriber is automatically connected at the exchange to an idle trunk terminating in an answering-jack, and in which blocking-arrangements are provided for preventing the seizure of a trunk leading to an operator at whose board there is already an unanswered call, selectors are employed of the type which pre-select an available trunk. Some groups of subscribers may have access to trunks which are distributed at different operators' positions, while other groups have access to trunks which all lead to the same operator. The blocking- arrangements are provided only in connexion with the former class. Another feature of the invention relates to systems in which connexions are made by A and B operators, who converse over order-wires, and consists in the use of pre-selecting switches for connecting an A-operator to the order-wire of an available B-operator. The switches employed are of the line-and-masterswitch type described in Specification 26,301/06. Figs. 2, 3 and 4 show an established connexion between subscribers T and T<1> on different sections of an exchange. The called subscriber T<1> belongs to a semi-automatic section, in which the operators are provided with impulsesenders to control automatic connectors at district offices at which the subscribers are grouped, while the calling subscriber T is on a purely manual section. Theoperations in effecting the connexion are as follows: - Line switch C and master switch F, Fig. 2. These operate as described in Specifications 1419/10 and 15,072/12. The subscriber is connected, as soon as he calls, to a pre-selected idle trunk terminating in a jack j. The relays 72, 73 are then energized over the calling line and the relay 72 energizes the relays 75, 81. The relay 75 closes a holding-circuit for the lineswitch C and the relay 81 lights up the calling- lamp 27. A pilot relay 28, common to all the incoming trunks at the operators' board, is energized in series with the lamp 27 and lights the pilot lamp 29. The relay 28 also serves to connect ground to the master-switch bank contacts a of all the " distributed " trunks which terminate in jacks at the same board (a distributed trunk being one which is allotted to a group of subscribers who also have access through other trunks to other operators, as explained above). These trunks are thereby marked busy to the line-switches C, and this condition endures until the call at the jack j is answered by the insertion of the plug p. Operators' cord - circuits and order - wire arrangements. When the answering plug p is inserted, a sleeve-circuit is closed through the relay 93, which de-energizes the pilot-relay 28 and the lamps 27, 29, and two circuits are closed for the supervisory relay 32 through the tip and ring of the plug, these circuits being controlled by the line relays 72, 73. Having ascertained the wanted number, the operator restores the listening key k<3> and presses the order-wire key k<1>. Her order-wire is connected to a pre-selecting switch D, Fig. 3, controlled by a master-switch F<1>, these switches being similar to the switches C, F, and the key k' closes at 101 a circuit for the winding 103 of the switch D, which connects her to the order-wire of an idle B-operator. (If all the B-operators accessible through the switch D were busy, the masterswitch F' would be in continual motion, and the contacts 115 being closed the A-operator would be notified by hearing the busy signal Q.) The A-operator inserts the plug p' in the jack j<4> of the trunk R allotted to her by the B-operator, and the B- operator inserts the plug p<2> at the other end of the trunk R into a jack j<5> connected by a two-wire trunk to a connector E, Fig. 4, at the district office to which the wanted subscriber belongs. The key k is then thrown to connect the impulse-sender 40 across the out-going trunk to control the connector. The same operation energizes the relay 132, which locks itself up through a contact of a relay 121 which is energized as long as the plug p<1> is in the jack j<4>. Connector E, Fig. 4. This operates as described in Specification 1298/10, except that the ringing-relay is cut out, when the called subscriber replies, by a separate relay 175 instead of by the reversing-relay 52. Supervisory signals and release. When the selecting-impulses have been sent, the key k is restored, and when the called subscriber replies, the relay 52 reverses the line connexions so as to energize a polarized relay 38, Fig. 3, which bridges the cord-circuit R and energizes the supervisory relay 33 in the cord-circuit 0, Fig. 2, thereby extinguishing the lamp 35. When the calling and called subscribers hang up their instruments, the relays 72, 73, 32, and the relays 52, 38, and 33 respectively, are deenergized, and the A-operator is notified by the lighting of the lamps 34, 35. She removes the plugs p, p<1>, and the B-operator, observing the extinction of the lamp 36, removes the plug p<2>, and the connexion is then entirely released. The line-switch C is not released until the plug p is withdrawn, its holding-circuit being maintained, after the subscriber T has hung up his instrument, by a relay 148, from which a shortcircuit is removed when the line-relay 73 is de-energized. The circuit of the relay 148 is through the upper winding of the supervisory relay 32, but its resistance is too great for the relay 32 to be energized in series with it.