Patent GB-132546-A (GB)
IPC: H04Q3/00
Abstract: 132,546. Western Electric Co., and Polinkowsky, L. Dec. 5, 1917. Semi-automatic exchange systems.-Relates to systems of the kind in which trunk or other special service calls are extended by a manual trunk operator to a switching-operator who extends the call over automatic switches to the wanted line. If the wanted line is busy, the local connexion may be broken down by the trunk operator in favour of the trunk call, by momentarily grounding the test terminal of the wanted line, after which a special busy tone is placed on this terminal indicating that the line is engaged in a trunk call. If the wanted line is idle, the trunk operator may ring it by depressing her usual ring- ing-key. The final selectors are used for extending both local calls and trunk calls, the supply of ringing-current being automatic in the first case, and under the control of the trunk operator in the second. The switching-operator is provided with signalling-means to inform her whether the trunk operator has taken for service the correct junction assigned by the switching-operator. The through-connexion of the switching-operator to the wanted line is prevented unless the trunk operator has taken for service the correct junction and unless the wanted line is idle. The invention is described as applied to a system in which the final selector, Fig. 3, is used for both local and trunk calls, while the first, second, and third selectors shown in Figs. 1 and 2 are used only for trunk calls. The trunk-operator's position shown on the left of Fig. 1 is connected by an orderwire to the switching-operator's position shown on the right of Fig. 1. It will be convenient to describe first the operation of the final selector in extending local calls and then the operations involved in the extension of a trunk call. Operation of final selector, Fig. 3, in extending local call. When the selector is taken into use for a local call, the line relay 372 is energized, moving the sequence switch into its second position. The brush chooser 373 and brush carriage 377 are set under control of the relay 372 in known manner in the second and fifth positions of the sequence switch, which then moves into its sixth position. Private branch exchange arrangements. The meter 398 and cut-off relay 399 of ordinary lines and of the last line of a group of branch exchange lines are shunted by a resistance 397 as indicated for lines 393, 395, whereas other branch exchange lines, such as 394, are not provided with this resistance. The resistances 397, 398, 399 are chosen so that the potential of the test terminals is such that, when connexion is made with a line provided with a resistance 397, whether such line is idle or not, or with an idle line not provided with a resistance 397, a relay 396 is energized in the sixth position of the sequence switch, and energizes a relay 380 so as to move the switch into its ninth position. If, however, connexion is made with the first branch exchange line, and this is busy, the potential of its test terminal is such that relay 396 is not energized, and a fresh circuit is closed over contacts 324, 319 for the 'brush carriage clutch magnet 377, which rotates the brushes until an idle line is found or, if necessary, until the last line is reached. In either case, the relay 396 is energized and the sequence switch is moved into its ninth position. Busy test and busy signal (local call). As the sequence switch passes through its eighth position, the selected line is tested by the relays 379, 380 in the usual manner, and if the line is idle, the relay 380 moves the sequence switch direct through to its thirteenth position. If, however, the selected line is busy, the switch comes to rest in its ninth position, wherein a relay 384 intermittently connects a tone-producer 351 over an interrupter 328 to a busy transformer 329 coupled to the calling-line. The connexion is released, as described later. Ringing-current (local call). In the thirteenth and fourteenth positions of the sequence switch, ringing-current is continuously supplied over contacts 312, 313 to the selected line. The relay 372 is energized by interrupters 381, 382 to move the sequence switch into its fourteenth and fifteenth positions successively. In the fifteenth position, ringing-current is supplied over an interrupter 326 and contacts 316, 313. When the called subscriber replies, relay 383 is energized and moves the sequence switch into its sixteenth or talking position, in which the incoming trunk is connected direct to the called line. The connexion is released after conversation, as described later. Setting up trunk call by operator. The final selectors, such as that shown in Fig. 3, are used for extending both ordinary and trunk calls, but the group-selectors shown in Figs. 1 and 2 are used only for trunk calls. As previously stated, the switching-operator at the automatic exchange tells the trunk operator which junction to use, and then depresses the assignment key 125 of this junction so as to associate therewith her controlling-equipment. The depression of the key 125 energizes a relay 126 which moves the sequence switch 100 into its second position, in which a lamp 127 is intermittently lighted by an interrupter 128, and a lamp 133 glows until the relays 131, 132 are energized by the trunk operator inserting the plug 129 in the jack of the assigned junction. (If the trunk operator inserts the plug in the jack of some other junction, the lamps 133 of both junctions glow.) A progress tone signalling-device 134 is connected over contacts 107, 108 to the trunk operator. The equipment-searching sequence switch 190 is also operated under control of the test relays 136, 137, to seize an idle registering and controlling equipment in known manner. When an idle equipment is found, the sequence switch 100 moves into its fourth position, and thence to its fifth position when the switching-operator has depressed the necessary keys. Operation of first selector, Fig. 1 (trunk call). In the fifth position of switch 100, the brush chooser 138 is operated in the usual way under control of relay 126, which, when the selection is complete, moves the switch 100 into its sixth position, wherein the brush carriage 141 rotates under control of relays 136, 137 to find an idle trunk in the selected group. The relay 136 then moves the sequence switch 100 into its eighth position, in which the fundamental circuit is extended overbrushes 143, 144 to the second selector. Second and third selectors, Fig. 2 (trunk call). When the second selector is seized, the relay 221 moves the sequence switch 200 into its second position, in which the brush chooser 222 is operated. In the third position, the brush carriage is rotated under control of the test relays 223, 224 to find an idle third selector. In the sixth position, the incoming circuit is extended to the third. .selector, and the test relay 223 disconnected. The third selector is operated in the same way as the second selector, and in the sixth position of the sequence switch 250, the fundamental circuit is extended to the final selector. Final selector, Fig. 3 (trunk call). The brushes of the final selector are brought to the terminals of the wanted line in the same manner as for a local call, the sequence switch 300 then passing from its fifth position into the ninth. As the switch 300 moves out of its fifth position, the high-resistance relay 371 is thrown into the test circuit, causing the relay 273, Fig. 2, to de-energize and move the sequence switch 250 into its seventh position. In the sixth position of switch 300, an idle private branch exchange line is selected, if necessary, as previously described, and then the switch 300 moves into its ninth position. As the switch 300 passes into its seventh position, a circuit is closed over contact 307 bottom, brush 276, Fig. 2, contact 257, for relay 271, which moves the switch 250 from its seventh to its tenth position. As the switch 250 is passing through its eighth position, the switch 300 is passing its seventh or eighth position, and a circuit is therefore closed through the left-hand winding of relay 372 over contacts 306, 253 top, and 256 bottom. The energization of relay 372 at this moment closes a circuit over contact 308 bottom and the right-hand winding of relay 385, which locks up over its left-hand armature and the armature of a relay 371 energized over the test lead. The relay 385 remains energized until the connexion is released. (When an ordinary call is set up over an ordinary third selector, the relay 372 is not energized when the switch 300 is passing through its seventh or eighth position, and, the relay 385 remains de-energized.) Operation when called line is idle. As the sequence switch 300 passes through its eighth position, the selected line is tested by the relays 379, 380 in the usual manner, and it the line is idle, the relay 380 moves the sequence switch into its tenth position by closing a circuit for its clutch magnet over contacts 311, 324. The sequence switch is arrested in its tenth position (instead of running through to its thirteenth position as in a local call) because of the energization of relay 385. In the tenth position of switch 300, the opening of contact 307 de-energizes relay 271, Fig. 2, which moves the sequence switch 250 into its thirteenth or talking position. At the end of the selecting operation, the controlling-equipment is disconnected and the relay 126 de-energized, thereby moving the sequence switch 100 out of its eighth and into its ninth position. If the toll operator has inserted the plug 129 in the assigned junction, the consequent energization of relay 131 moves the switch 100 on to its eleventh position, from which, since the selected line has been assumed to be idle and therefore the relay 140 deenergized, it moves at once into the thirteenth or talking position. With swi