Patent GB-177140-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/62
Filed: 1922-01-05
Abstract: 177,140. Automatic Telephone Manufacturing Co., Ltd., (Assignees of Lomax, C. E.). March 16, 1921, [Convention date]. Automatic, semi-automatic, and manual exchange systems.-Relates to the provision of special night calling arrangements and conference facilities in an automatic private branch exchange. A system is described in which an automatic P.B.X., Figs. 3 and 4, is connected over trunks such as 428, 429 with a main exchange, Figs. 1 and 2, which is in a transition stage, being equipped with both manual and automatic connecting apparatus. Incoming calls at the P.B.X. are dealt with by an operator, but local calls, and also outgoing calls initiated by privileged subscribers, whether to the main exchange or to another manual exchange, are established automatically. The operation of the P.B.X. is unaffected when the main exchange is cut over from manual to automatic working. In manual working the trunk 428,429 is normally connected to battery at the main exchange through a calling relay 425, Fig. 1, and in automatic working it is connected to battery through the line relay 602 of a line switch C', Fig. 2. In both cases a high-resistance polarized relay 27, Fig. 3, is normally energized over the trunk, but when the trunk isseized, whether by the P.B.X. operator or by a. cord O or connector H<2> at the main exchange,- the current supplied to the trunk is reversed and the relay 27 relapses and marks the trunk busy at the P.B.X. Ringing current from the main exchange, whether supplied from a cord O orfrom a connector H<2>, operates a calling relay 25, Fig. 3, which locks itself and bridges its lower winding metallically across the trunk, and thereafter acts differentially, so that if the call is abandoned before being answered by the P.B.X. operator it is de-energized by the consequent reversal of the trunk current to normal. When the call is answered by the P.B.X. operator the bridges through the relays 25, 27 are opened and the trunk is bridged by a high-resistance circuit across the cord O<1>, but when the operator presses her answering key the resistance is lowered, and is maintained low after the restoration of the key, to operate the supervisory relay in the cord O or the back-bridge relay of the connector H<2>. The P.B.X. operator completes the wanted connection by controlling a connector H over the sleeve circuit of the jack J<3>, this circuit including a jack spring which is only closed when the plug P<1> is fully inserted. When the subscriber answers the call the bridge across the cord O<1> is opened and a metallic feed circuit from the main exchange is extended through the cord and connector to the called line. The connection is supervised by the operators at both exchanges. When the called subscriber disconnects himself the bridge circuit across the cord O<1> is restored. If the main exchange is working manually the taking down of the cord O reverses the current in this bridge, or if the main exchange is working automatically the disconnection of the calling subscriber momentarily short-circuits the current in the bridge, in both cases lighting a supervisory lamp in the cord O<1>, but at the same time a low-resistance bridge is closed across the cord O<1>, in the one case to mark the trunk busy at the main exchange and in the other case to keep the connector H<2> from releasing, until the P.B.X. operator takes down the cord O<1>. For night service the trunk 428, 429 is connected by a cord O<2> to a night line N, having a series of bells at different points in the P.B.X. building, so that a call from the main exchange mav attract the attention of a watchman. The watchman goes to the nearest telephone such as A, Fig. 4, and operates a connector H<1> to connect himself to the line N and so to the main-exchange trunk. A night call to the main exchange can be made in this way from any of the P.B.X. substations, whereas calls made in the ordinary way over the tenth level of the connector H<1> can only be made by certain privileged subscribers. The local connectors H' are also provided with special means for enabling conference conversations to take place between a number of the P.B.X. subscribers simultaneously. Call from main exchange (operating manually) to P.B.X. The calling subscriber A<2> is connected by a cord O to an idle trunk 428, 429 terminating in a jack J<2> at the P.B.X. A high-resistance polarized relay 27, Fig. 3, is normally energized over the trunk 428, 429 but after the energization of the cut-off relay 426, Fig. 1, reverse current is supplied from the cord O and the relay 27 de-energizes, closing a circuit for the relay 28, which marks the trunk busy to local calls. The main-exchange operator presses a key K<6> to transmit ringing-current to energize a high-resistance alternating-current relay 25, which locks itself through its upper winding, short-circuits the condenser in the bridge circuit through its lower winding, and lights the call lamp L'. (If the main-exchange operator should withdraw the plug P" before the P.B.X. operator answers, the reversal of current in the trunk puts the two windings of the relay 25 in opposition, so that this relay is unlocked, and the re-energization of relay 27 restores the circuits). When the P.B.X. operator answers the call with her cord O<1>, relays 26, 50 are energized in the sleeve circuit. The relay 26 unlocks the relay 25 to extinguish the lamp L<1> and opens the initial circuit of the relay 28, but this relay is kept energized by the jack springs 71. A relay 52 is now energized in a bridge circuit across the cord O<1>, but its resistance is too high to permit the energization of relays 53, 54 in series in the same bridge, or of the supervisory relay 421 in the cord O. When the P.B.X. operator throws her listening key K<1> the relay 52 is short-circuited and the relay; 53, 54, 421 become energized. The relay 421 extinguishes the lamp L<12>, to show that the P.B.X. operator has answered, and the relay 53 closes a contact 67 to keep the relay 52 short-circuited after the key K<1> is restored. Previously, however, to restoring the key K' the operator inserts the plug P<1> in the jack J<3> of an idle connector H, Fig. 4, and operates her dial S to call the wanted subscriber, the dial being now connected in the sleeve circuit in series with the relay 150. This circuit includes a jack spring 80, so that the relay 150 cannot be falsely actuated through the tip of the plug but only when the plug is fully inserted. The connector operates in known manner to select, test, and ring the wanted line. When the subscriber A<1> answers, the supervisory cord relay 55 becomes energized, extinguishing the lamp L<6> and opening the bridge circuit across the cord O<1>. Conversation now takes place, the P.B.X. subscriber being fed with current from the main exchange. Supervisory signals; release. When the called subscriber disconnects himself, the relay 55, Fig. 3, lights the lamp L<6> and restores the high-resistance bridge 53, 52, 54 across the cord O<1>, thus de-energizing the relay 421, Fig. 1, which lights the lamp L<12>. When the main-exchange operator with draws the plug P", the current in the trunk 428, 429 is reversed to normal, so as to de-energize the relay 52, Fig. 3, and the relays 54, 52, 53 being now for the first time all deenergized a c rcuit is closed for the relay 51, which locks itself up and lights the lamp L<5>. The relay 51 also connects its lower winding in a low-resistance bridge across the cord O<1> so as to energize the trunk line relav 425, Fig. 1, which prevents the sluggish relay 427 from deenergizing and keeps a busy mark on the sleeve of the jack J<1> until the P.B.X. operator withdraws the plug P, whereupon the relays 26, 28 also become de-energized and the trunk circuits are restored to normal. P.B.X. night service. When the P.B.X. operator goes off duty she plugs up a special night cord O<2> to connect the trunk 428, 429 to a watchman's circuit N, having bells 98, 99, 100 at various points of the building. Ringing current from the main-exchange does not energize the relay 25, which is now disconnected at the jack spring 15, but rings the bells 98, 99, 100. A watchman hearing the call goes to the nearest telephone, such as A, Fig. 4, and calls the number representing the night line N, to which he is connected by a connector H<1>. A shaft contact 338 is closed when the connector is set to this line and energizes the ringing cut-off relay 305 in series with a relay 304, which bridges an inductance 303 across the line. At the termination of the final digit the switching relay 308 is energized in the usual way in series with a relay 91, Fig. 3, which disconnects the call bells and grounds the sleeve circuit to mark the trunk busy and to energize the relay 26, which opens the bridge through the relay 27. Conversation then takes place over the night line N. Calls from P.B.X. operator to main exchange. These are made by plugging into a jack J<2> and throwing the key K to energize the relay 80<1> and to bridge the operator's head-set across the tip and ring of the plug P. Relay 26 is energized in the sleeve circuit and open-circuits the polarized line relay 27, which energizes the guard relay 28 in a circuit including the jack-spring 71. The line relay 425, Fig. 1, is now energized over the trunk 428, 429 and lights the calling lamp L". Calls from P.B.X. subscribers to main exchange; restricted service. A subscriber A desiring to call the main exchange raises a connector H<1> to its tenth level, at which the shaftsprings 330 - - 333 are operated. The springs 330, 331 energize the ringing cut-off relay 305 in series with the relay 304, which bridges the inductance 303 across the outgoing side of the connector. The springs 332, 333 connect the armature 323 direct to ground 269 over a fourth wiper of the line switch C, preparing circuits for the t