Patent GB-429767-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1933-12-06
Abstract: 429,767. Automatic exchange systems. AUTOMATIC ELECTRIC CO., Ltd., Strowger Works, TAYLOR, R., 30, Oulton Road, Wavertree, both in Liverpool, and BAKER, G. T., Blackbrook, Caerphilly, Glamorgan. Dec. 6, 1933, No. 34341. [Class 40 (iv)] Bi-directional call-finders hunt in both directions of motion by the operation of self-interrupting stepping magnets, release being effected by re-operation of the rotary magnet which steps the switch forward out of the bank, the switch then dropping and rotating back to normal similarly to the switch described in Specification 391,123. The driving and testing circuits are controlled from common apparatus but release is independent thereof. The system described is similar to that described in Specification 376,265 in which regular finders are directly connected to first group selectors whereas overflow finders are connected thereto over secondary finders, but the three control circuits normally dealing respectively with calls in three groups of levels have provision for dispensing with the use of one of them by a simple change of connections. Three secondary start groups SS1, Fig. 9, are provided, for starting the secondary finders SFS, two of which are started by two control circuits SC1 associated with each start group. Normal operation. A regular finder is preselected by a testing circuit over wiper R1 of distributer RPD, windings of LK in series, and relay G, Fig. 6 which interacts with magnet RPM the circuit of which includes contacts of normally operated relay RFZ, Fig. 5. Relay L of the calling line makes an individual marking in bank P1 or P2 of the finder and a level marking in bank VB. One of relays SA ... SE, each associated with two levels, pulls up and energizes start relay ST of a control circuit. As shown, three control circuits PC1, Figs. 6 to 8, PC2 and PC3, Fig. 5 are provided, as described in Specification 376,265, for use normally in calls from three sub-groups of levels respectively, and in case of congestion for calls from any sub-group. If the connections between terminals U26, U28 and U30, U32 are removed and connection made between terminals U24, U26 and U28, U30, control circuit PC3 may be dispensed with. Start relay ST completes a circuit for both windings of LK in series to battery at the group selector, and LK makes a circuit for its lower winding in series with relay VR and magnet RPM which does not operate. Current flow over LK (lower) is now opposed to that over LK (upper) but the resultant flux is sufficient to hold LK operated unless another control circuit is testing simultaneously in which case the LK relays of both circuits start to release and the quickest one restores holding current to the other. Slow-to-operate relay VR pulls up after LK, locks up, operates SF, Fig. 8, in series with one winding of the line relay at the group selector, connects LK to the vertical bank VB, and operates switching relay HA in the finder so that idle battery from the group selector is disconnected, and LK falls back. Relay DV pulls up, completes the vertical test circuit over LK and itself, and connects ground from st1 to the vertical magnet VM which steps by self-interruption until LK operates over the vertical bank, simultaneous testing by two circuits being dealt with by the LK relays as before. RS (lower) now pulls up in series with ST and magnet RPM, locks up, transfers the original circuit for ST to ground at lk2, and operates switching relay HB over R1 of RPD. Relay DV falls back and makes a self-interrupting circuit over R8 for rotary magnet RM which is opened when test relay PA or PB pulls up to battery in bank P1 or P2 of the finder. Relay CO, Fig. 8, now pulls up, holds SF (upper) and releases ST which is followed by LK, VR, RS and finally by PA or PB. The relapse of RS kicks off the distributer RPM and the release of PA or PB short-circuits CO which falls back and releases SF. The appropriate switching relay HA or HB remains held in series with K in the line circuit. If calling lines are encountered simultaneously over wipers P1 and P2, test relay PA takes precedence since it opens the circuit of PB. Release. When the switching relay falls back, ground on common conductor 22 makes a self-interrupting circuit for RM, the switch moves out of the bank, drops and rotates to normal where the circuit of RM is opened. As the rotary magnet remains energized until the switch is completely restored, it is arranged that the rotary pawl does not engage the ratchet after the stepping motion has been completed. Overflow conditions. When all the regular finders are busy, battery (negative) over the vertical wipers in normal position disappears from common conductor 23, Fig. 5, so that the grid of thermionic or gas-discharge valve VAA becomes positive and relay RFB in the anode circuit pulls up. A metal rectifier MRA in the lead from each finder to the common conductor 23 prevents a ground over R1 of RPD from shunting battery of idle finders. It is now assumed that the regular finder shown is an overflow finder connected to banks O1 ... O8 of outflow distributer OPD, the dot and dash connections in Figs. 4 and 5 replacing the dash connections in Fig. 4. RFB shunts out the normally operated relay RFZ which removes the short-circuit on and prepares to hold OFC, Fig. 6, and corresponding relays in PC2, PC3, and operates OS, Fig. 9, which controls contacts in each secondary control circuit such as SC1 to remove ground from the bank O1 of overflow distributer OPD and replaces it by battery from relay DS and resistance YA, Fig. 9, in parallel. The ground in question marks overflows busy in the case where regular and overflow finders are connected to the primary distributer. When magnet RPM of the primary distributer is kicked off subsequent to the setting of the last regular finder, wiper R1 encounters ground and G pulls up completing the circuit of OFC which, together with its relief relay OFR, replaces the primary distributer by the secondary distributer OPD. Similar operations occur in control sets PC2, PC3. Relays ST, LK, VR operate as before except that the circuit for LK passes over wiper O1 to start relay DS of the secondary control circuit, Fig. 9, which is held over vr3. Relays OFC, OFR are also held over vr3 to prevent their release if, meanwhile, a regular finder should become idle, metal rectifier MRB being inserted in the circuit to prevent premature operation of DS from rfz5. The overflow finder is now set in the same manner as the regular finder. When the overflow finder was seized, it was marked, by battery over SF, and 04, in the banks of no-normal secondary finders such as SFS and two of these are started up by DS, Fig. 9, so that primary and secondary finding proceeds simultaneously. A secondary finder is preselected by a testing circuit over SE1, DK, IG in which 1G alone is operated by busy ground and interacts with magnet SEM. When start relay DS operates, DK pulls up and removes the shunt over DR which shunts down DK, these relays serving to prevent double switching similarly to LK, VR in the primary control circuit. DR busies the group selector, prepares the test-circuit over FK and makes a self-interrupting circuit for finder magnet SFM which is opened by FK when the primary finder is picked up. The shunt on FR is now removed and FK, FR obviate double switching by two secondary finders. In the primary control circuit, SF operates in series with test relay FK, brings about the release of the primary control circuit, and releases the start relay of the secondary control circuits. When the primary (overflow) finder switches through relay FK, Fig. 9, falls back and operates the switching relay SK of the secondary finder, relay 1G pulls up to kick off the secondary distributer SED and short-circuit DR which releases FR followed by 1G so that the secondary circuit is restored to normal. All overflows or secondary finders busy, statistical metering. When the last overflow finder is taken into use, battery is disconnected from common lead 28, Fig. 5, and relay OFB in the anode circuit of valve VAB pulls up and prepares a circuit for OFZ which operates when VR relapses on restoration of the control circuit after the last finder has been set. Relay OFZ transfers the start circuits of PC1, PC2, PC3 to statistical meters over leads 29-31. If a regular finder becomes idle, RFB controlled by valve VAA releases whereupon RFZ pulls up to switch the control circuit over to the regular finders. If all secondary finders of the two groups controlled by start relay DS become busy, OB falls back and operates FB which disconnects the start relay DS grounds the access points S1, S2 of these groups and opens the circuits of the 1G relays of the two secondary control circuits to disable the distributers. Faulty circuits. When a primary control circuit is taken into use, LK tests for idle batterv on bank R1 and if this is absent due to a disconnection, the distributer is stepped on due to non-operation of LK. A similar test is made by DK in the secondary control circuit. A faulty control circuit is dealt with by the usual " S " and " Z " pulses started up when start relay ST pulls up and operating respectively relays TA, TB. Relay TB connects up individual, rack, and general alarms, releases ST, transfers the start circuit from PC1 to PC3 and removes a short circuit from TC, Fig. 8. If the control circuit has become associated with a finder (VR, RS or PA operated) TC is immediately operated in series with the finder switching relay HA, busies the finder over R1, opens the line testing circuit over R3, PA to prevent the line being busied, and otherwise disables the finder. When the fault is cleared TB which has been locked to ground in control circuits PC2, PC3, is released by removal of link FRL If a finder fails to release, the rotary magnet RM remains energized and an alarm is operated in the common lead 22.