Patent GB-752912-A (GB)
Title: Telephone system employing impulse responsive cross bar switches
IPC: H01H67/26
Filed: 1954-03-05
Abstract: 752,912. Automatic exchange systems. AUTOMATIC ELECTRIC LABORATORIES, Inc. March 5, 1954 [April 29, 1953], No. 6528/54. Class 40 (4). An automatic exchange system uses a switch with a primary shaft 355 and a number of group shafts 360, a motor 365 responding to a first train of impulses to step the primary shaft, and means responsive to the stopping of the primary shaft to couple a selected group shaft to the primary shaft so that a second train of impulses applied to the motor drives the selected group shaft, the stopping of the group shaft operating a selected set of contacts. Use is made of the switch described in U.S.A. Specification 2,680,783. Operation. When subscriber 10 closes his loop, relay 110 operates to energize start relay 200 of the allotter. Those relays such as 280, 290 corresponding to idle finders are in operated condition. Operation of 200 therefore energizes finder start relay 140 of the first idle finder, transfer relay 230, and timing relay 235, which energizes another timing relay 240. Relay 240 locks up and operates 260 to restore 235, which vibrates its armature 236 to start a timing operation for a kick-off circuit. When this vibration stops 240 and 260 release. Meanwhile operation of 140 has looped conductors 400, 401 to operate line relay 420 in the connector, locked the appropriate finder relay, say 280, and extended the finder control circuit from the allotter to the first linefinder mechanism, Fig. 3. Operation of line relay 420 in the connector energizes release relay 425, pulsing relay 410 and hold relay 430. A motor 365, of the type described in Specification 649,427, [Group XXXV], co-operates with interrupter relay 210 and cam contacts 396, 398 to rotate primary shaft 355 <1>/11 of a revolution at each cycle. When wiper 328, driven in synchronism with the shaft 355, finds the group containing the calling line, group test relay 220 pulls up in series with interrupter relay 210 to stop motor 365, restore 210, restore transfer relay 230 slowly, and operate transfer magnet 356. Magnet 356 disconnects wiper 328 and pulls trigger bar 359 to the left to bring the selected group shaft 360 into driving engagement with the primary shaft 355. Release of transfer relay 230 de-energizes magnet 356, which however remains locked mechanically, and recloses the motor circuit. The motor again co-operates with relay 210 and contacts 396, 398 to drive the selected group shaft 360, cams 364(1)-364(0) closing the associated cross-points in turn. When the calling line is found line test relay 250 operates to stop the motor and release of 210 energizes finder switching relay 150. 150 operates line cut-off and lock-out relays 130, 120, the former restoring line relay 110. Finder switching relay 150 also operates guard relay 215 in the allotter and restores 280, 215 restoring start relay 200 to restore 140, 150, 220, 240, 250, 260 and finally 215. Statistical metering. If the finder should fail to find the calling line within a given time the timing relays release the allotter which then reoperates and passes the call to the next idle finder. When the last idle finder is taken into use all the distributer relays 280-290 are in released condition and reset relay 265 operates to re-energize all allotter relays whose associated finders are again idle, so restoring 265. If all finders are still busy, however, 265 holds up and all-trunks-busy relay 270 falls back to operate a meter. If another call is initiated during this condition an overflow meter OF is actuated. Dialling wanted number. When finder switching relay 150 operates the control circuit for connector line relay 420 is extended back to the calling line as previously described and dial tone from lead 502 is returned to the calling line. Relays 425 and 504 hold up during each digit. Line relay 420 responds to the first digit and is followed by pulsing relay 410 which causes stepping magnet 465 to advance wipers 472, 473 of an auxiliary switch and close off-normal contacts 468, 469. Local call. In the case of a local call, restoration of 504 at the end of the first digit energizes local-call relay 515 over wiper 472 to disconnect dial tone, switch the pulsing circuit to motor 665, and energize release switch to restore the auxiliary switch, 467 then relapsing. Relays 420, 410 repeat the second digit to motor 665, relays 504, 510 holding up during the digit. At the end of the digit transfer magnet 656 operates to provide driving engagement between the primary shaft 655 and the selected group shaft 660. Relays 420, 410 repeat the third digit to motor 665 to select and close a crosspoint, transfer relays 504, 510 operating to energize digit-transfer relay 535. When 504, 510 restore digit-transfer 540 pulls up in series with 535 to switch the pulsing circuit back to the auxiliary switch so that the fourth digit steps the auxiliary switch wipers 472, 473, the latter selecting a ringing code, transfer relays 504, 510 holding up again during the pulsing. If the called line is busy, ground on its CN conductor operates busy relay 460 over test lead 580 so that at the release of 504, 510 busy tone from lead 503 is returned to the calling subscriber. If the called line is idle, release of 504 operates switching relay 570 which starts or maintains a ringing generator 553. The interrupter pulses leads PU, PUH to operate ring pick-up relay 440 to apply ground impulses from the appropriate contact R1-R0 selected by wiper 473 to relay 550 to produce an intermittent ringing code. A portion of the ringing current leaks back through condenser 565 to provide ringing tone. When the called party answers ring cut-off relay 560 pulls up, completes the talking connection, and restores ringing relay 550. Back-bridge relay 445 also energizes to operate battery reversing relay 415. At the end of conversation the switches are driven forward to home position. When the group shaft, say 660, reaches home position a stud 672 slips into a hole in the frame and the shaft is withdrawn from driving engagement with the primary shaft by spring action. When the primary shaft 655 reaches home position after a total of 44 half-steps off-normal contacts 688 open the motor circuit while a cam releases latch 666 to return trigger bar 659 under spring action. P.B.X. calls. The test and extra control terminals of each line of a P.B.X. group, except the last, are jumpered as at 619. If then the first line is busy the operation of digit transfer relay 540 causes operation of interrupter relay 530 to ground on the test wire over the jumper. Relay 530 reoperates 504, 510 and advances motor 665 a further half-step, whereupon contacts 699 open to release 530 to stop the motor after another half-step when it has reclosed contacts 699. The next line is then tested and so on. Calls to other exchanges. A first digit of 8, 9 or 0 causes the first six impulses to drive the auxiliary switch. When wiper 472 reaches the sixth contact it operates trunk-call relay 520, which locks up, cuts off dial tone, and transfers the pulsing lead 483 from the auxiliary switch to motor 665, which responds to the remaining impulses of the digit. Relay 520 prepares a trunk-hunting circuit, operates switch-through start relay 450, restores 535, and energizes release magnet 467 to restore the auxiliary switch. Jumpers 619 are used on the trunks of the group selected so as to cause the motor 665 and relay 530 to interact until an idle trunk is found. When transfer relays 504, 510 restore, relay 405 operates in series with 450 to release line relay 420 and extend the talking conductors 400, 401 to the outgoing repeater by way of leads 500, 501. Absorbing single impulses. A first digit of 1 is absorbed. When the auxiliary switch responds, 504 operates and then releases to close a release circuit.