Patent GB-379749-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1931-06-04
Abstract: 379,749. Automatic exchange systems. ASSOCIATED TELEPHONE & TELEGRAPH CO., 1033, West Van Buren Street, Chicago, U.S.A. June 4, 1931, No. 16402. Convention date, July 14, 1930. [Class 40 (iv).] Finder-switches are provided with polarized test relays of the kind described in Specification 272,872, [Class 38 (v), Electric switches &c.] which require current in the proper direction in both windings to effect operation, so that false operation due to booster metering battery cannot occur. The systems described employ bi-directional double-wiper finder-switches arranged in two groups normally serving corresponding groups of calling lines, with means whereby either group may serve both groups of calling lines in exceptional circumstances. One system employs allotting-switches which include control relays for the finders, while in the other system the finders are brought into use in turn by means of chain starting circuits, the control relays being disposed in common equipment. Normal operation of finder, Figs. 1 and 2. Assuming the subscriber S calls, line relay 201 applies marking battery through cut-off relay 202 to the test terminals and ground to start wire 260 and to the appropriate terminals of vertical banks VA, VB. Start relay 163 in the allotter DA energizes in series with the magnet 164 (inoperative), and relay 161 energizes in series with the upper polarizing windings of the finder switching relays 104, 105 and locks. Line and release relays 102, 101 of the selector SA pull up, disconnecting one of the holding grounds from busy relay 162, and the vertical magnet 109 of the finder FA operates by interaction with stepping relay 166 to raise the wipers to the appropriate level, whereupon change-over relay 165 energizes over vertical wiper 262, locks and connects in the rotary magnet 108. Relay 166 again controls stepping, and the lower windings of switching relays 104, 105 are now connected to test wipers 231, 234, so that one or other pulls up in series with cut-off relay 202 when the calling line is reached. It is to be noted that the switching relays by virtue of their polarizing windings cannot be operated by reversed booster battery on the test terminals. The operated relay 104 or 105 switches through and remains held over its polarizing winding and the test wire. Operation of the allotter DA. When the finder FA switches through, the magnet 164 energizes over wiper 149 or 150 and wire 136, and disconnects start relay 163. Relay 161 falls back and disconnects the magnet 164 and change-over relay 165. The allotter therefore moves out of engagement with the finder FA and continues to step as long as busy finders marked by ground over wiper 147 are encountered. If, after start relay 163 energizes, relay 161 fails to pull up due to the finder FA or selector SA being off-normal or due to some fault, change-over relay 165 has time to energize and connects up the magnet 164 to preselect another idle finder. If the operated finder fails to switch through within a predetermined time, relay 160 energizes over vibrating springs 199 controlled by relay 161, locks, disconnects busy relay 162 and connects up the magnet 164 to advance the allotter as before. The relapse of busy relay 162 extends start wire 260 over start wire 26], so that calls in the A group are now transferred to the allotter DB, Fig. 3, of the B group. Busy relay 162 also relapses with similar results when all the finders of the A group are in use, hunting of the allotter being prevented. Relay 160 releases should all the finders of the B group become engaged, and brings the allotter DA into service again. Operation of the allotter DB, Fig. 3, which differs in certain respects from the allotter DA. Start relay 359 connects up relay 362 which energizes unless short-circuited over wiper 347 due to the finder FB or the selector SB being off-normal or due to some fault, and the finder operates under control of stepping relay 361 and change-over relay 360. Relay 362 maintains busy relay 358 independently of the finders. On operation of switching relay 304 or 305, ground is extended over wire 336 to energize the magnet 363, which disconnects relay 362 and the allotter advances to preselect the next idle finder. A differential relay 357 is arranged to energize alternately over its upper and lower windings under control of relays 360, 361, 362 so as to maintain its springs 377, 378 in vibration. If, due to a fault, the circuit over either winding exists long enough for these springs to come to rest, differential relay 356 pulls up and sends an impulse to the magnet 363 to cause a fresh finder to be preselected. Two-step relay 355 energizes, operating an alarm relay 353, and relays 356, 357 are disconnected. If now differential relay 356 is again operated, relay 354 energizes to connect in an emergency alarm, since the trouble is probably in the allotter. Busy relay 358 is released to transfer calls in the B group to the allotter DA, Fig. 1. Finders with chain starting circuit, Fig. 4. Start relay 464 energizes over wire 261 and connects battery to the chain circuit 451 to operate associating relay 405 in the allotted finder FAM. Relay 463 energizes in series with the polarizing windings of switching relays 406, 407, and the finder operates as in Fig. 1 under the control of stepping relay 466 and change-over relay 465. When switching relay 406 or 407 pulls up, relay 462 energizes and disconnects start relay 464, which on relapsing removes a short-circuit from transfer relay 404 so that the latter energizes, locks, releases relays 405, 462, 463, 465 and extends the chain circuit 451 to the next finder. The locking circuit of relay 404 through its upper winding is opened when the finder returns to normal, but that through its lower winding is maintained until all the finders of the group have been taken into use in order to preserve the proper sequence. When the last finder is taken into use, common relay 461 falls back and releases the relays 404 of all the idle finders, and then re-energizes over the multiple grounds provided thereby. If, however, all the finders are still in use, all the relays 404 are held locally and relay 461 remains back and connects start wire 261 to start wire 260 of the B group. If, after start relay 464 energizes, relay 463 fails to pull up, change-over relay 465 energizes as in Fig. 1 and start relay 464 falls back momentarily to allow transfer relay 404 to operate and extend the chain circuit to the next finder. If the operated finder fails to switch through, relay 460, similar to relay 160, Fig. 1, operates to extend start wire 261 to the B group.