Patent GB-422570-A (GB)
Abstract: 422,570. Automatic exchange systems. AUTOMATIC ELECTRIC CO., Ltd., Strowger Works, Liverpool. July 15, 1933, No. 20087. Convention date, July 16, 1932. [Class 40 (iv)] In a system employing by-path control circuits in which the control circuit at the penultimate stage serves also as a register-controller for controlling the final selector, there being no control circuit at that stage, the register-controller controls the final selector by revertive impulsing as regards the tens digit and by forward impulsing as regards the units digit. The register switch RS2 which takes the hundreds digit and marks the bypath switch subsequently takes the tens digit without restoring, and is then stepped by revertive impulses until it again reaches the position to which it was first set and which is now marked by the by-path switch. The units register RS3 after taking the units digit is stepped on to normal by impulses sent concurrently to the final selector. Link circuit comprising finder F and secondary switch SS. Relay 501 energizes upon operation of line relay 105 and connects up start relay 502 in each of the distributers D1, D2, which hunt for an idle link giving access to a secondary group containing an idle first selector. Magnet 508 operates in a local circuit controlled by group-test relay 503 which tests over wiper 527 for earth normally applied to wires such as 135 in each of the by-path control circuits associated with a secondary group, and in circuits over wipers 521, 526 over which relay 504 tests when 503 is up for absence of earth on wires such as 154, 157 indicating an idle link. Relay 504 upon operation connects up magnet 134 of the secondary switch SS, and polarized test relay 507 pulls up to battery on an idle trunk. The arrangement is such that if all the trunks become busy before an idle trunk has been found, 503 falls back and restarts the link testing operation. The operating circuit is now transferred to magnet 114 of the finder F, and polarized test relay 506 pulls up when the calling line is reached, whereupon earth is connected over wiper 525 to operate switching relay 115 and the distributers are restored to normal condition. First selector FS1 and by-path control circuit BPS1. The loop is extended through relay 202 to line relay 606 in the by-path, and dialling tone is sent back. Release relay 603 energizes due to the removal of a short-circuit. The first digit is repeated to the marking switch RS1, series relay 605 operating at the first impulse and connecting up relay 601, which closes a stepping circuit for magnet 610, so that the by-path switch BPS1 advances over groups of trunks as the impulses are received under the control of relay 604 and wiper 620. At the end of the digit, the switch stands on the first trunk of the wanted group, and relay 605 falls back after 604 has finally pulled up and initiates the hunting operation, polarized test relays 608, 609 being connected to wipers 614, 618. Assuming an idle trunk is engaged by wiper 614, 608 pulls up and extends the loop to the penultimate selector PU1. If on the other hand 609 pulls up, it connects 608 in parallel with itself. Line and release relays 606, 603 falls back, but earth fed back over test wiper 614 holds relays 608, 601 to maintain the by-path and associated selectors guarded. Magnet 203 now operates under control of relay 607 which energizes over wipers 205, 615 when the selector FS1 reaches the trunk selected by the by-path switch BPS1 and connects up switching relay 201. Relay 601 falls back, the switches RS1 and BPS1 restore to normal, and the by-path becomes available for use in further connections. Penultimate selection PU1 and registercontroller DR1. The loop is extended through relay 307 to line relay 711 in the registercontroller, and release relay 801 energizes in series with 802 due to the removal of a shortcircuit, earth being fed back over wire 346 to hold the established connection. The hundreds digit is repeated to the marking switch RS2, series relay 802 operating at the first impulse, and the by-path switch BPS3 advances over groups of trunks as the impulses are received under the control of relay 804 and wiper 830, the stepping circuit for magnet 810 being closed by relay 709 when 804 pulls up after the first step of the marking switch. At the end of the digit, the by-path switch stands on the first trunk of the wanted group, and series relay 802 relapses after 804 has finally pulled up and initiates the hunting operation which takes place under the control of polarized test relays 807, 808. Assuming 807 pulls up, a circuit is closed for magnet 310 to advance the selector PU1 into engagement with the selected trunk, whereupon 806 energizes over wipers 322, 822. Final selector C1 and register-controller DR1. In response to the tens digit, the switch RS2 advances a corresponding number of steps from the position in which it is standing. Series relay 802 operates as before, and after the first step, 804 falls back and connects up 805. On the relapse of 802 at the end of the digit, a circuit is closed for relay 710, which starts the control of the final selector. 709 restores, connecting up 704 and transferring the impulse circuit to the switch RS3 on which the final digit is registered. The final operation of 802 connects up 703, this relay and 710 remaining locked to wires 346, 720. Relay 708 is now connected to wiper 821, while earth is connected to wiper 824, and a fresh stepping circuit is closed under the control of 708 for the switch RS2, which takes a single preliminary step. In the final selector, start relay 403 energizes over wire 332, connects wire 329 through its upper winding to wipers 410, 414 and closes a self-interrupting circuit for magnet 404. At this time, earth is connected to the last six contacts in each group of ten in the banks of wipers 410, 414, so that a revertive impulse is transmitted as each group is passed over to operate 708, so that the switch RS2 advances one step. Assuming the tens digit to be 6, after the preliminary step mentioned above, RS2 stands 7 steps ahead of the position marked by wiper 830 of BPS3. After 3 revertive impulses therefore, that is, when the final selector C1 reaches the beginning of the 4th group, RS2 again reaches the marked position and a circuit is closed through 805 for 803, which opens the locking circuit of 805, so that at the next impulse, 805 falls back while 803 remains locked. Tens cut-off relay 709 is connected up and energizes when a shunt is removed by the next operation of 708 in response to the 5th impulse when the final selector reaches the 6th contact of the 5th group, and removes earth from wiper 824. In the final selector, 402 operates due to the removal of a short-circuit over wire 332, placing magnet 404 under the control of wipers 410, 414 and opening the holding circuit of 403. The selector therefore stops at the beginning of the 6th group, where the circuit of relays 403, 708 is opened, and magnet 404 is then connected to wire 332 in readiness for receiving the final digit. If the tens digit is 0, RS2 is set to the position marked by wiper 830, so that when 710 operates to start the control of the final selector, 803 responds immediately and remains locked after RS2 takes its preliminary step. A single revertive impulse from the selector operates 708 and tens cut-off relay 709 energizes. On the relapse of 708, series relay 802 being back, 702 energizes in series with the locking circuit of 703 and connects up 701, whereupon 708 energizes locally and disconnects 701, so that these relays interact. Each time 701 operates, an impulse is sent over wiper 824 to the final selector, while each time 708 operates, an impulse is transmitted to the switch RS3. This action continues until RS3 regains its normal position, the number of impulses thus being the complement of the units digit, when units cut-off relay 707 energizes and 701, 708 both fall back. If the units digit is 0, RS3 already stands in its normal position, and an immediate circuit is closed upon operaof 702 for units cut-off relay 707, so that no impulses are sent. Busy test, ringing and completion of the connection. Relay 704 remains energized during impulsing, and busy relay 705 is now connected over wiper 821, wire 329, switching relay 401 to test wipers 409,413, while on the relapse of 704, this circuit is transferred to idle relay 706. If the wanted line is busy, 705 energizes but not 401 and connects earth to wire 343, whereupon line relay 302 of the penultimate selector PU1 energizes in series with 304 and connects up release relay 303 to release the register-controller, while 304 gives a busy signal. If the wanted line is idle, 706 energizes, shunts its upper winding to allow switching relay 401 to operate and connects earth to wire 344 to energize line and release relays 302, 303. Relay 303 transfers the calling loop to line relay 302 and connects up switching relay 308 and metering relay 305. Ringing current is sent through ring cut-off relay 306, which responds on the reply of the called party and disconnects 305, a booster metering impulse being sent back during the relapse of the latter. Back-bridge relay 301 pulls up and reverses the connections of line relay 302. Meanwhile in the register-controller, line and release relays 711, 801 fall back, the switches which are off-normal restore and the operated relays release. When the calling party hangs up, the link F, SS and first selector FS1 release, while the penultimate and final selectors PU1, C1 remain held under the control of the called party. All trunks busy at the first selector stage. One or more pairs of overflow trunks are connected to the earlier positions of the by-path switches preceding the first group and are multipled over as many groups of selectors as may be desired. If the by-path switch BPS1 finds no idle trunk in the group marked by RS1, on stepping out of the group, 604