Patent GB-771793-A (GB)
Title: A single motion numerical switch
IPC: H04Q3/00
Filed: 1954-04-21
Abstract: 771,793. Automatic exchange systems. AUTOMATIC ELECTRIC LABORATORIES, Inc. April 21, 1954 [May 1, 1953], No. 11529/54. Class 40 (4). In a single-motion group selector or final selector employing wiper-switching, the groups of outlets are arranged in staggered formation in two or more sets of contact banks, so that the switch wipers travel less than the length of one group in order to reach the beginning of the next group; a self-interrupter circuit for the switch magnet is completed, during reception of a series of impulses, over a common control wiper and bank, the circuit including alternately each of two control conductors multipled respectively to two mutually interspersed sets of contacts of the control bank. As shown, an allotter, Fig. 3, is associated with a group of line-finders including LF, Fig. 2, which serve a group of a hundred line circuits and associated subscribers' lines of the kind shown in Fig. 1. Each line-finder of the group is associated with a different group selector, such as that shown in Figs. 4 and 5, although a plurality of finders of different groups may be associated with the same group selector. In the group selector, and also in the final selector, Figs. 6 and 7, the evennumbered groups are arranged in one set of contact banks and the odd-numbered groups in another set, the two sets of groups being mutually staggered as described above, Subscriber A, Fig. 1, calls subscriber B, Fig. 7, whose directory number is 237. Line relay 120 operates, substitutes battery for earth on the line-finder test lead 15, and earths the start lead 18 to the allotter, Fig. 3, where start relay 310 is energized to disconnect an alternative start relay 320 and bring up relay 350. This connects relay 360 in a battery-checking circuit which extends over allotter wiper DS and offnormal contact 66, Fig. 4, in the group selector associated with the line-finder LF. The all otter has pre-selected LF by hunting until wiper DC1 failed to encounter earth. If for any reason, such as LF being in fact busy or faulty or the group selector being off-normal, the batterychecking circuit is incomplete, relay 360 is not operated. The allotter driving magnet 300 is energized, relay 350 falls back, and magnet 300 by self-interruption drives the allotter until an outlet is reached at which wiper DC1 again fails to find earth. Relay 350 re-operates and the battery-checking process is repeated. When battery is found, relay 360 operates, followed by relay 340 which connects common test relay 335 in series with the finder driving magnet 230 and also connects the junction of 335 and 230 to the finder test wiper 23. In the group selector, relays 420, 440 and 430 are energized so that earth is returned over lead 47. Two possibilities now arise: (i) Line-finder LF is already standing on the calling line. There is then no earth on lead 15 to shunt test relay 335 which therefore operates, followed by relay 330 which disconnects magnet 230, leaving 335 in a battery-checking circuit over finder test wiper 23, and also completes a circuit for slowoperating switching relay 210. If battery is properly connected to lead 15, test relay 335 holds in series with the calling line's cut-off relay 110, which is energized and releases line relay 120, while relay 210 completes its operation and extends the calling line to the group selector, the allotter now being released to hunt for the next idle line-finder. If, however, battery is not found on lead 15, test relay 335 falls back, preventing the operation of switching relay 210 and energizing the finder magnet 230. Relay 330 releases, de-energizing magnet 230, which advances the finder one step, and reestablishing the circuit by which relay 335 and magnet 230 test for absence of earth on wiper 23 in its new position. If the line is not calling, earth is found to shunt and release relay 335, and magnet 230 by self-interruption advances the finder until wiper 23 fails to encounter earth, whereupon relay 335 tests for battery as before. (ii) If the line-finder LF is not standing on the calling line, it hunts for it as just described above. If LF is faulty and fails to find a calling line, the allotter is advanced in search of another idle finder by the relapse of relay 360 following the operation of relays 390 and 395 by earth pulses from a timer apparatus (not shown). All finders busy. If all the 1st-choice linefinders are busy, the removal of earth from lead 41 by the operation of all the switching relays 210 or 220 brings about the release of relay 380 (which is normally operated) when relay 340 falls back on the release of the allotter. The test circuit is thereby switched from wiper DC1 to wiper DC2, giving access to 2nd-choice finders. If all these also are busy, the consequent removal of earth from lead 42 causes another normally-operated relay 370 to fall back, opening the circuits for relay 350 and magnet 300 and so disabling the allotter. The relapse of relay 370 may also operate a meter (not shown). Group selector, Figs. 4 and 5. The calling line has now been extended from the line-finder LF and relays 420, 430 and 440 are energized. The calling subscriber A receives dialling tone from lead 71 and dials the first digit " 2 " of the wanted number. Relay 420 responds to the impulses and interacts with relay 450 to cause magnet 480 (by self-interruption to earth over control wiper 97) to step the switch to the start position of the wanted group. Relay 440 releases at the end of the digit, and if the digit is even, as in the present case, wiper-switching relay 460 operates as well as relay 470 to join control conductors 77, 78 and 79 in order to control the hunting of the switch for an idle outlet in the selected group, which is indicated by absence of earth on test wiper 93. Relay 410 switches through to the final selector, Figs. 6 and 7, where relays 620 and 630 are energized, and relays 420, 470, 430 and 450 fall back. If all outlets in the group are busy, the switch stops at the last position, where wipers 93 and 97 are no longer connected together, and the relapse of relay 450 brings up relay 440 to return busy tone from lead 73; when the calling subscriber hangs up, the apparatus.is released, an overflow meter is operated over wiper 98, and the switch goes home. Restricted service. Restricted groups have no earth connected to their start positions in contact barik SC, and non-privileged subscribers have no earth connected to lead 16 in their line circuits. If both these conditions occur in an attented call, no circuit exists to operate relays 460 and 470, and the calling subscriber hears busy tone following the relapse of relay 440. Final selector, Figs. 6 and 7. Relays 620 and 630 have operated, followed by 625 and 660. The calling subscriber dials the tens digit, causing relays 620 and 680 and magnet 655 to advance the switch in a similar manner to that described above in connection with the group selector. At the end of the digit, relays 625 and 660 fall back, wiper-switching relay 600 operates if the digit is odd, and relay 690 operates to complete an impulsing circuit for magnet 655 and to re-energize relays 625 and 660. The units digit is repeated by line relay 620 to magnet 655 which accordingly sets the switch to the wanted line, relay 680 operating at the first release of 620 and relay 625 releasing at the end of the digit so that busy relay 650 tests the line over wiper 191 (or 188) for idle battery or busy earth. Relay 660 releases, and, if the line is free, relay 670 is energized to release relay 680 and initiate ringing. When the called subscriber B answers, ring cut-off relay 640 operates to bring up back-bridge relay 610 and switch through the speech circuit. If, however, the test wiper 191 (or 188) encounters busy earth, relay 650 operates and busy tone is returned from lead 157. Spark-quenching arrangements. Each switch is provided with two spark-quenching devices, one of lower effectiveness, such as a non-linear resistance element 51, 55 or 76 or a condenserresistance combination 173, 173a, connected to a point between the magnet and the interrupter contact, and one of higher effectiveness, such as a germanium diode rectifier 53, 54, 74 or 174, connected to a point between the test wiper on the one hand and the magnet and interrupter contact on the other hand. That part of the system which is concerned with non-numerical switching, Figs. 1-3, and part of Fig. 4, forms the subject-matter of Specification 771,794. Specifications 642,586 and 754,855 also are referred to.