Patent GB-191219250-A (GB)
Title: Improvements in or relating to Telephone Systems.
Filed: 1912-08-22
Granted: 1913-09-22
Abstract: 19,250. Automatic Telephone Manufacturing Co., [Automatic Electric Co.]. Aug. 22. Semi-automatic exchange systems. - In a system in which numerical switches at an automatic branch exchange are controlled by operators at a main exchange, one set of switches at the branch exchange serves to interconnect subscribers belonging to the branch exchange, while a second set is used for establishing connexions from cord-circuits at the main exchange to subscribers at the branch exchange. In the case of local connexions between subscribers at the branch exchange there is no connexion to the main exchange during the conversation of the subscribers, since the inter-exchange trunk over which the operator controls the selective switches is released as soon as the connexion has been completed. A calling subscriber A. Fig. 1, at the branch exchange is connected by his line-switch C to an idle connector E, and an operator is signalled over the wires 118, 124. Fig. 2. If the wanted subscriber also belongs to the branch exchange, the connexion is made by the connector E, which is controlled by the operator's impulse-sender 87 over a two-wire inter-exchange trunk 124, 125. This trunk, which is used only for controlling the connectors of the series E, is automatically connected by a switch H over lateral wires 133, 134 to any connector E which has been taken into use by a line switch C. The switch H is constructionallv similar to the line-switches C and is operated by the same master-switch D, but its action is functionally that of a call-finder. When the operator has completed the connexion by means of the connector E the switch H and trunk 124, 125 are at once released, so as to be available for further controlling-operations. The connector H is organized so that reverting calls can be made on party lines. If the wanted subscriber belongs to the main exchange, as A', Fig. 2, the operator effects the connexion backwards from a cord circuit O to the calling subscriber by a special connector F at the end of a trunk 170, 171. The connector F is controlled by the operator's impulse-sender 87 over one wire of this trunk, the return circuit being through ground. In the case of connexions made through the connector F, both subscribers are supplied with current from the operator's cord-circuit. The main exchange may have connexions with a purely automatic exchange. Connexion of the subscriber A, Fig. 1, by his line switch C, to an idle connector E, and by the switch H, Fig. 2, to an operator O. The line switch C and master switch D are of the general type described in Specification 26,301/06 and their circuits are the same as in Specification 1419/10. When the subscriber A lifts down his receiver, the switch C connects his line to the next idle connector trunk E at the contacts 15, 19, 21, 17, and the relays 102, 103 are energized. The relay 103 provides a holding-circuit for the line-switch winding 25 and closes a circuit through springs of the relay 222 and over the wire 118 to a relay 108, Fig. 2, which in turn closes a circuit through springs of the switch H and over the trunk wire 124 to a relay 130, which lights a calllamp 131<a>. The operator replies by throwing a key K<1> to connect her instruments Q across the trunk 124, 125, which is thereupon connected hy the switch H to the lateral wires 133, 134 from the connector E, this being effected as follows. The bridging of the trunk 124, 125 energizes the line-winding 135 of the switch H, which closes a circuit from ground G<50>, through springs of the relay 108, switch H, and relay 144, over the wire 142, Figs. 2 and 1, to the master-switch relay 38, which energizes the motor magnet 32 so as to rotate the plunger of the switch H (as well as all the idle lineswitches C) from the position to which it was moved when the trunk E was first occupied. When the wiper 143 of the auxiliary bank M<1> comes on to the grounded terminal 109 of the connector E, a circuit is closed through the relay 144, which energizes the pull-in winding 145, which operates the plunger of the switch H so as to connect the trunks 124, 125 to the wires 133, 134. The relay 144 also open-circuits the wire 142, so that as soon as the next idle connector trunk is reached the relay 38 is deenergized and the master-switch brought to rest. Upon the actuation of the switch H, the connector line relays 51, 52, Fig. 1, and a slow-release relay 156, Fig. 2, are energized in series with the operator's instruments. The relay 156 energizes the cut-off winding 157 to hold the switch H after the pull-in winding 145 has been open-circuited. The operator now enquires the wanted number. Operations when the subscriber A wants a subscriber A<1> on the main exchange. In this case, the operator asks the calling subscriber to give his number and then to hang up his receiver so as to release the connexions. She then rings up the wanted subscriber and connects him back to the calling subscriber through the connector F, Fig. 1, as described later. Operation of the connector E by the operator when the subscriber A wants another subscriber on the same branch exchange. In this case, the operator calls the wanted number on her impulse-sender 87. The resulting current-interruptions de-energize the connector line-relays 51, 52. A slow-release relay 59, which was energized previously by the relay 51, remains energized throughout, so that each time the relay 51 de-energizes, it closes a circuit through the vertical magnet 53, which lifts the wipers 43, 44, 45, 45<a> to the required level, and through the slow-release private-magnet relay 55, which, together with the private-magnet 50 which it controls, de-energizes at the end of the series and causes the side-switch arms 49 &c. to move to second position. The second set of interruptions in the same way operates the rotary magnet 54, which rotates the wipers 43, 44, 45, 45<a> to the terminals of the wanted subscriber, and the side-switch then moves to the third position. The operator finally sends an extra numeral (no matter what) to energize, over the side-switch arm 49 in its third position, a relay 222, which locks itself up, closes a second circuit for the release relay 59, connects a guarding ground potential through the lineswitch spring 19 to the test wire 193<a> to mark the calling subscriber busy, and opens the circuit 118 leading to the auxiliary masterswitch bank M'. Supply of ringing current. The ringing up of the wanted subscriber may be effected by the operator, or the operator may disconnect herself and leave the ringing-operations in charge of the calling subscriber. In the first case, the operator grounds both sides of the trunk 124, 125, whereby the relay 52, but not the relay 51, is de-energized. In the second case, the subscriber presses a button 2 to cut a resistance into his line-circuit, whereby the relays 51, 52 and 102 are de-energized but not the more highly-wound relay 103. The result in either case is to close a circuit through the ringer relay 60, which connects the generator L to the wanted line. Release of the switch H. When the operator restores the key K<1>, the relay 156 is de-energized and releases the switch H, which, being of the self-alining type, immediately takes up a position opposite to the terminals of the next idle connector of the series E. Release of the line switch C and connector E. The relay 222 and line-switch winding 25 are held locked over the alternative grounds G<3>, G<18> until both subscribers have hung up their receivers, de-energizing the relays 103, 102, 51, 52. The line switch is then released and the relay 222 de-energizes, open-circuiting the connector release relay 59, which energizes the release magnet 56. Busy signal. If the wanted subscriber had been busy, the private magnet 50 would have remained energized, when the relay 55 became de-energized, by a ground connexion over the test wiper 46 and side-switch arm 48, In this case, the side-switch would remain locked in its second position and the subscriber A, on putting his receiver to his ear, would hear a busy signal from the device I, which remains connected over the springs of the magnet 50. Reverting party-line calls. Each subscriber at the branch exchange has two separate testterminals in the connector banks, the connectors being provided with two test-wipers. This arrangement enables a reverting call to be made to a subscriber on the same party-line as the calling subscriber, for a busy ground potential is not applied to the upper of the two test-terminals of the calling subscriber until the connector relay 222 is energized after the side-switch has passed to its third position. The connector E, when making a reverting connexion, tests this upper terminal only, the private magnet 50 being connected to the upper test wiper 45, and accordingly finds the calling line disengaged and completes the connexion. On the other hand, a busy ground potential is applied to the lower terminal by the relay 103 as soon as the connector E is seized by the calling subscriber, thus rendering the calling line at once busy to the connector F, which tests both the upper and lower terminals. Connexion of a main-exchange subscriber A<1> to a branch-exchange subscriber A through the cord O and connector F. The operator inserts the plug P<1> into the jack J<1> belonging to the trunk 170, 171, which terminates in the connector F at the branch exchange. She then throws the key K<2> to connect her instruments to the tip of the plug and operates her impulse- Sender 87 to send the necessary sets of currentinterruptions over the trunk wire 170 and through a relay 71. At its first energization the relay 71 closes the circuit of a slow-release relay 72, and at each succeeding de-energization a circuit is closed through the slow-release private-magnet relay 73 and the vertical magnet 67. The wipers 64, 65, 66 are thus raised to the desired level, and the relay 73, to