Patent GB-293294-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1928-02-27
Abstract: 293,294. Associated Telephone & Telegraph Co., (Assignees of Lomax, C. E., and Saunders, N. H,). July 2, 1927, [Convention date]. Automatic exchange systems. - In a system employing call-finders, two groups of finders have access in common to sub-groups of lines which are accessible to the two groups of finders in opposite order of priority. Normally, each group of finders is controlled by a particular allotter and deals only with calls from particular sub-groups of lines, but if all finders of the group are busy, an idle finder of the other group selected by another allotter deals with the call. The finders of both groups are connected up to each allotter but one group is normally marked busy in each allotter, an attendant's control key being provided to enable one allotter to control both groups if the other allotter is faulty. Another control key is provided to effect a routine test of the equipment. The system described comprises two groups A, B of call finders represented by finders FA, FB comprising 200-point switches with two sets of wipers, each finder being associated with a group selector EA, EB which is prepared for use before the setting of the finder is completed. The finders of groups A and B appear respectively in the first halves of the contact banks of allotters DA, DB and also in the last halves of the allotters DB, DA. The lines of a group of subscribers are multipled through both groups of finders but in the regular and reverse order respectively, the lines in the first five levels of a group of finders constituting the sub-groups of lines from which a call is normally dealt with by a finder of that group only. The vertical hunting movements of the finders are controlled by additional test wipers and vertical contact banks such as VA, VB, contacts 2 to 9 of the two groups being multipled together in the reverse order. The first contacts are only multipled in the individual groups and the last contacts are permanently grounded to secure the arrest of the finders. Normal operation of call finder FA and allotter DA in response to a call from subscriber S numbered 125. Subscribers' line relay 201 at 213 removes ground from private wire 256 and places ground over 214, 250 on the second level of vertical test bank VA of the finder, this ground being extended over resistance 251 and conductors 260, 437 to start relay 405 of allotter DA to complete at 429 a circuit for auxiliary start relay 402 in series with magnet 410. Relay 402 at 417 closes a holding circuit for busy relay 404 which is normally operated by ground returned over 161, 436 by idle finder-selector links, and at 419 completes a circuit over 447, 163 for line relay 102 (upper) of group selector EA which is thus prepared for operation. Relay 402 also completes a circuit for stepping relay 107 of finder FA over springs 120, 121 of the rotary and vertical magnets 104, 105, conductor 162 to ground at 418. Relay 107 and vertical magnet 105 interact until 107 and 106 energize in series over 158, vertical test wiper 262 and ground on the second level of VA. Relay 106 locks up, changes over the circuits and immediately energizes rotary magnet 104 which makes the first rotary step and releases 107. It will be noted that, on non-calling levels, a circuit is completed for 107 and 106 from ground over two of the resistances 251 in series so that these relays do not energize. Ground from a non-calling line over test-wiper 234 now energizes 109 to transfer the circuits of FA to the other wiper set 230 - - 232, 107 being re-energized by ground from non-calling lines over wiper 231 to re-operate the rotary magnet.. Test wiper 234 bridges adjacent contacts so that 109 does not fall back when this wiper passes over grounded contacts. When, however, this wiper loses ground, 109 de-energizes to prevent further energization of 107, and switching relay 108, being no longer short circuited by ground on the test wiper and at 113 at the selector EA, operates in a circuit in series with 107 which does not now energize. The line is switched through and cleared in the usual manner. Relay 108 also connects ground from 135 to conductor 164 to operate relay 403 which at 421 removes the ground connected to the upper speaking wire over 447, 163, and at 422 opens the circuit of 402. Relapse of 402 opens the holding circuit of 106 at 418, and at 420 completes the circuit of the allotter magnet over wiper 415 and ground at off-normal contact 140 in the finder FA. The magnet steps the allotter until it arrives at an idle finder. Indicating class of calling line. Switching relay 108 connects discriminating tone over 133 to the release trunk conductor 151 to indicate to a toll operator the class of service to which the subscriber is entitled. All finders of group A busy and transfer of the call to group B equipment. Busy relay 404, which is normally held operated as described in the previous paragraph, now falls back and at 426 breaks the above traced circuit of 402 and makes a connection to conductor 439 so that if 405 is energized due to a call normally dealt with by group A finders, ground at 429 is extended over 439 to auxiliary start relay 604 of allotter DB in series with magnet 610, and the call is dealt with by an idle finder in group B. The circuit of magnet 410 is also opened at 427 to prevent the allotter DA from hunting uselessly. When a finder in group A becomes idle and if the group B equipment is not dealing with a call, busy relay 404 reoperates from ground at the idle finder-selector link over 161, 436, 630, 435 and the idle finder is seized by DA. Operation of call finder FB and allotter DB. This is substantially identical with that of the group A equipment described above. Statistical metering. Relapse of the busy relays 404, 602 when all the finders of the respective groups are busy, closes the circuits of meters 407, 611, and if all finders of both groups are busy, a circuit is completed for meter 406 over contacts controlled by meters 407, 611 to ground at 429 or 620 when start relay 405 or 601 is energized as the result of a call. Defective circuits, arrangements for dealing with; fault signals. If the 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 the control of the other allotter. When key K1 is thrown to the left, conductor 260 leading from vertical test bank VA is connected at 501 to the corresponding conductor 261 of VB so that if S initiates a call, start relay 601 of allotter DB is energized, the circuit of start relay 405 of DA being simultaneously broken. At 502, busy common lead 161 of FA is connected to the corresponding lead 367 of FB so that busy relay 602 of DB is maintained energized by idle finder-selector links of both groups, the circuit of busy relay 404 of DA being simultaneously broken. At 503, conductors 440, 441 and therefore wipers 605, 606 of DB are connected together. The conductors, such as 165, of finders of group A are connected up to the second half of the bank of wiper 606, and since the busy mark has been removed from the second half of the bank of 605 by the deenergization of 404 in DA, allotter DB can now hunt for an idle finder of group A over the second half of the bank of 606 in addition to its normal hunt over the first half of the bank of 605 for an idle finder of group B, the circuit of its magnet 610 being traced over 640, 623, 634, 441 to wipers 605 and 606. The other leads, such as 162-164, of group A finders are connected up to the second halves of the banks of 609-607 respectively of allotter DB so that the remaining operations of DB in conjunction with PA are similar to its normal operations in conjunction with FB. when key K1 is thrown to the right, allotter DA controls the finders of both groups A and B in a similar manner. If allotter DA seizes a defective finderselector link, relay 402, energizing as a result of a call, completes a circuit over 422, 436, 443 for a lamp 636 and slow alarm device (not shown). In normal operation, or during a routine test as described in the next paragraph, the circuit is broken at 423 by the operation of relav 403 when the finder switches through. The alarm circuit is similarly controlled by relays 604, 603 of DB. Routine testing. Operation of key K2 places ground over conductors 512 or 513 on the fifth level of VA or VB to energize the start relav 405 or 601 of the corresponding allotter. If there is no traffic at the time, a finder preselected by the allotter takes five vertical and eleven rotary steps, switches through, releases the allotter and then releases itself. The allotter moves on to the next finder and the test continues until all the finders have been exercised. If a call is made during the test, it is dealt with in the normal manner, and the test subsequently continues.