Patent GB-297318-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1928-08-21
Abstract: 297,318. Associated Telephone & Telegraph Co., (Assignees of Saunders, N. H.). Sept. 17, 1927, [Convention date]. Addition to 293,294. Automatic exchange systems.-Relates to the system, described in the parent Specification, in which two groups of call finders have access in common to a group of lines divided into two subgroups, each group 'of finders normally being under the control of an allotter individual to the group and dealing with calls from a particular sub-group of lines. Arrangements were provided for cutting out a faulty allotter and bringing all finders under the control of one allotter which then selected a finder to deal indiscriminately with calls from either sub-group of lines. The present invention comprises a modified allotter which preselects only finders of the group normally associated with it but which, when controlling both groups of finders, picks out an idle finder of the other group after a call, normally dealt with by that group, has been originated. The system shown is identical with that described in the parent Specification with the exception of the allotters DA, DB and their interconnecting circuits shown in Figs. 4, 5 and 6. Constructionally, the allotters comprise mechanism similar to Strowger switches but utilizing only the rotary movement, the switches having two sets of wipers which have access respectively to the two groups of finders. The two subgroups of lines which appear respectively in the first five levels of the group A and group B finders are hereinafter referred to as group A and group B lines. Normal operation of allotter DA, Fig. 4, in response to a call from group A. Ground placed by calling line on one of the first five levels of the vertical test back VA of group A finders, is extended over 260, 502, 475 to start relay 409 which at 463 closes a circuit for relays 406, 401 in series. Relay 401 does not energize but 406 closes a circuit at 453 for the normally operated all-finders-busy relay 405 to maintain it energized while the finder is being set even though it is the last idle finder. Relay 406 also opens the circuit of wiper 427 at 451 to prevent operation fo the allotting switch and at 449, 450 completes circuits over wipers 424, 425 respectively for starting the finder FA and preparing the associated selector EA as described in the parent Specification. When relav 108 switches the finder through, it completes a circuit over 135, 164 and wiper 426 for relay 407 which at 457 opens the circuit of relay 406 the relapse of which completes a circuit from ground over off-normal springs 140 of finder FA and wiper 427 for stepping relay 401 of the allotter. Relay 401 and magnet 410 intereact to step the allotter on to an idle finder which fails to return ground over wiper 427. If the wipers are stepped off the last contacts of their banks, relay 403 operates over cam springs 437, locks itself over 440 and offnormal contacts 436, opens the circuit of stepping relay 401 at 439, and at 441 completes the circuit of release magnet 411 so that the allotter returns to normal with its wipers on the contacts of the first finder of the group. The allotter then continues the hunt for an idle finder if the first finder is busy. All finders of groups A busy, transfer of call to group B equipment. When the, last finder such as FA goes off normal, conductor 161 loses ground at idle finder-selector links and all-findersbusy relay 405 of allotter DA falls back when its holding circuit over 453 is broken on the relapse of relay 406. The stepping circuit of DA over wiper 427 is broken at 445, and at 447 the circuit controlled by start relay 409 is switched over to start a finder in group B. This circuit extends from 463 over 447, 478, 647, 637 to relays 604 and 609 (in series) of allotter DB. Relay 604 starts a finder in group B in the same manner as relay 406 of DA started a finder in its group, but group B finder takes more than five vertical steps since group A lines appear in the upper levels of group B finders. It will be noted that when busy relay 405 of DA relapsed, it opened at 446 its direct energizing circuit over 473, 501, 161 so that if ground is placed on 161 by an idle finder of group A while a call is being dealt with by group B, relay 405 will not re-energize until 604 of DB relapses to complete a circuit for relay 405 over 472, 510, 642, 473, 501, 161. A group A finder is thus prevented from being started up to hunt for a calling line in group A during the hunting of a group B finder for the same calling line. Operation of allotter DB. This is identifical with that of allotter DA, the relays 601 - - 609 having the same functions as relays 401 - - 409 taken in the reverse order. Defective circuits, arrangements for dealing with. If allotter DA or DB is defective, the throwing of key K1 to the left or right respectively cuts out the faulty allotter and brings its group of finders under control of the other allotter. The operation of allotter DA with K1 thrown to the right will be described. Allfinders-busy conductor 367 and start conductor 261 of group B are now connected to conductors 474 and 476 of allotter DA. When a call in group B is initiated, relay 408 is energized by ground on 261 and at 459 extends the busy conductor 367 to relay 404 which pulls up (if there is an idle group B finder) and at 443, 442 changes over the circuits of DA so that it is now controlled by wiper set 420 - - 423 the banks of which are multipled to the banks of the normal wiper set 620 - - 623 of allotter DB. The circuit of stepping relay 401 is now effective over 435, 439, 443 and wiper 420 to ground at busy group B finders. Relay 401 and magnet 410 interact to step the allotter on to an idle group B finder when relay 402 pulls up over 461, 444, 456, 443 and relay 401. Relay 402 opens the circuit bf wiper 420 at 434, and at 432, 433 respectively completes the circuits for starting finder FB and preparing selector EB. When the finder FB is switched through by relay 302, relay 407 energizes over wiper 421 to ground at 330 in finder FB and opens the circuit of 402 at 456 so that allotter DA may step on to the next idle group B finder if a call from that group is pending. If no call from that group is pending, relay 408 falls back followed by 404 and the allotter is free to preselect an idle group A finder. If, when a call from group B is initiated, there is no idle group B finder, relay 404 does not pull up when 408 energizes but relay 406 pulls up over 461, 444, 457 in series with relay 401 and a preselected group A finder is started up to hunt for the call as described for the normal operation of allotter DA. Fault signals. When relay 406 or 402 of allotter DA pulls up in the normal or emergency operation of the allotter, a circuit is closed for lamp 412 through a slow alarm device (not shown) but is normally broken when 407 energizes on the switch through of the finder. If the finderselector link is faulty, this circuit is maintained and an alarm is given. Routine testing. Operation of key K2 places ground over 512 or 513 on the fifth level of VA or VB to effect a test of the equipment as described in the parent Specification.