Patent GB-169443-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/62
Filed: 1921-09-19
Abstract: 169,443. Automatic Telephone Manufacturing Co., Ltd., (Assignees of Willis, B. D.). Sept. 22, 1920, [Convention date]. Automatic and semi-automatic exchange systems.-A trunk line is rendered accessible as long as a relay bridge across the trunk is in its operated condition, but when the circuit through the relay is broken due to the trunk being faulty, the relay closes a circuit to mark the trunk busy. The invention is described as applied to a semi-automatic system in which a manual subscriber A, Fig. 1, is connected over an operator's cord circuit O at the manual exchange, and an idle trunk 36, 37 to a private branch exchange operator's position M, Fig. 2, where an impulse sender S is operated to extend the line to a wanted automatic subscriber A', Fig. 3, over the connector H. An automatic subscriber A<1>, by dialling the digit O, may connect himself directly to the main exchange over his line switch C and an idle selector connector (not shown), the tenth level of which is allotted to trunks (as 77, 79) leading to the main exchange. A polarized relay 52, Fig. 2, is connected across a condenser in the left-hand winding of a repeating coil in the trunk line at the P.B.X, and normally is in the position shown. When the circuit of the polarized relay is broken by a fault, or reversed by the manual exchange operator plugging into jack J<3>, Fig. 1, to use the trunk, the left-hand side of the armature 61 is pulled up and completes a circuit for the relay 54 which marks the trunk busy. Another feature of the invention is the provision of means at the P.B.X. whereby the operator, by throwing a key K<1> and operating her impulse sender S, can connect each trunk line to a particular automatic subscriber before leaving her position for the night. In this condition the particular automatic subscriber and the main exchange are continuously in direct connection, but the trunk line is still accessible for extending calls from other automatic subscribers. Connection of a manual subscriber A, Fig. 1, to an automatic subscriber A<1>, Fig. 3. When the operator plugs into the jack J<3> a circuit is completed for the relays 17, 30. Before the insertion of the jack J<3> the polarized relay 52, Fig. 2, was energized over the line relay 31, Fig. 1, and was held in the position shown, but owing to the inclusion of a high resistance 40 in this circuit the relay 31 was inert. When the jack J<3> is plugged, the relay 16 is substituted for the relay 31 in the circuit of the polarized relay 52, and the direction of the current being reversed, the armature 61 completes a circuit for the slow release relay 54, which earths the release conductor 78 and completes a control circuit 70, 66, 75 from the line relay 100 of the connector H, Fig. 3. The main exchange operator now signals the P.B.X. operator by throwing the key K and sending current over the trunk line, thus causing the armature 61 to vibrate. A short circuit is thereby removed from the relay 53, which responds and completes a circuit for the lamp L<5>. The P.B.X. operator depresses her listening key K<2>, energizing the relay 51, which locks up and short circuits the resistance 40, causing the relay 16 at the main exchange to respond and extinguish the lamp 12. Having been informed of the number of the wanted subscriber, the P.B.X. operator connects her impulse sender S in the control circuit by depressing the key K<3>, and extends connection to the wanted subscriber A<1>, Fig. 3, in known manner over the connector H. After dialling, the key K<3> is restored and the supervisory lamp L<4> is illuminated over the circuit 58, 76, 130, 131. When the called subscriber answers, a line relay 50 is energized over the called line and de-energizes the relay 51, which cuts out the lamp L<4>. When the calling subscriber A hangs up the relay 15 relapses and the supervisory lamp L<1> is lighted. On the called subscriber A' replacing his receiver the relay 50, Fig. 2, is de-energized and the short-circuit is removed from the resistance 40. The relay 16, in the manual operator's cord circuit 0, Fig. 1, thereupon relapses and completes the circuit of the supervisory lamp L<2>. The cord circuit O may now be disconnected. The removal of the plug from the jack J<3> reverses the current through the polarized relay 52, which is restored to its normal condition and de-energizes the relays 54, 53, the latter extinguishing the lamp L<5> and breaking the control circuit of the connector H, which releases in the usual manner. Connection of an automatic subscriber A<1>, Fig. 3, with a manual subscriber A, Fig. 1. On removing the receiver at substation A<1> the line switch C operates to select a trunk line leading to an idle selector connector (not shown) of known construction, and the subscriber dials the digit O to raise its wipers to the tenth level in which they hunt to find the contact set, for instance 80, 81, 82, Fig. 2, in which the first idle trunk to the main exchange is terminated. The switching relay 55 is then energized over the release trunk conductor 78, and locking up over its armature '68 disconnects the section of the trunk leading to the connector H. The relay 50 is now energized over the calling line, and in addition to completing a circuit 63, 65, 69 for the relay 54, short-circuits the resistance 40, causing the response of the line relay 31 which lights the line lamp L<3> to signal the main exchange operator, who enquires the wanted number and extends connection in the usual manner. The relay 54 grounds the conductor 78 to mark the trunk busy. Supervision at the main exchange is controlled as described in the previous paragraph. Night connections. Before leaving for the night, the P.B.X. operator permanently extends each trunk line to a particular automatic subscriber. This is accomplished by throwing the key K<1>, thereby closing the control circuit of the connector H by earthing the conductor 75 through a resistance, which prevents overheating of the line relay 100. The key K<3> is then depressed, and by operating the sender S the trunk is extended to a particular subscriber, say A<1>, who is advised that he is connected up for night service. The key K<3> is now restored and the control circuit maintained energized over the key K<1>. By plugging into the jack J<3> the manual operator may signal the subscribed A<1> direct. When the subscriber A<1> answers, the relay 50 is energized and completes a circuit for the relay 54, which grounds the release conductor 78. The subscriber A<1> is able to call the main exchange by simply lifting his receiver, thereby energizing the relay 50 which short-circuits the resistance 40, causing the response of the relay 31 and the illumination of the lamp L<3>. An automatic subscriber not having special night service facilities may use the trunk line to call the main exchange in the ordinary manner over a selector connector, unless the release conductor 78 is made busy by the trunk being in actual use.