Patent GB-401354-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1932-05-12
Abstract: 401,354. Automatic exchange systems. AUTOMATIC ELECTRIC CO., Ltd., Strowger Works, Liverpool. May 12, 1932, No. 13735. Convention date, May 29, 1931. [Class 40 (iv).] In a system using A.C. impulses of a particular frequency for control and supervision, certain of the impulses are of various predetermined lengths and produce three or more different effects in accordance with the lengths of the impulses. Impulses of predetermined length are used for switch setting, release, trunk offering, while the length of other impulses such as for seizing a repeater and for answering supervision, are immaterial, all impulses being converted from A.C. to D.C. and vice-versa at repeaters. The invention is described in connection with both-way repeaters RI, R2, R3, Fig. 1, in a network comprising a manual exchange and automatic exchanges A, B. In a call from the manual operator to an automatic subscriber, the operator receives a clearing signal when the subscriber hangs up and, on clearing, an A.C. impulse is transmitted to the automatic exchange to release the apparatus thereat. In a call from automatic to manual, however, the subscriber sends the clearing signal and also releases the automatic apparatus so that it is necessary to re-seize the automatic apparatus by a further signal from manual in order that the release signal sent when operator clears may release the automatic apparatus instead of re-seizing it. The dialled A.C. impulses are repeated in D.C. form by an impulse-correcting relay set, which the same relay set, running through two cycles instead of one, controls the length of a back release impulse. Call through manual to exchange A. The operator answers a call with plug P1, Fig. 2, and throws K to the left so that 200 operates and locks up in series with 232 in listening set OTC to connect the set to the calling line. On insertion of calling plug P in the trunk circuit TC, Fig. 3, relay 303 operates in the sleeve circuit in series with 274 in the operator's control circuit which energizes 278 to light the supervisory lamp 215. Relay 303 operates 367 which connects A.C. signalling current to the junction 1, 2 over lamps 375, 376. The A.C. supply as shown comprises a frequency doubler consisting of a transformer 377 with a centretapped primary over the halves of which current is caused to flow in the same direction during successive half-cycles of the 60-cycle source by means of metal rectifiers 378, 379. Relay 367 also operates slow-to-operate relay 322 from ground at jack J which had also energized 360 to pull up its slow weighted armature 361 to complete a circuit for slow-to-operate relay 362 which closes a further circuit to hold 367 until both circuits are opened by 322. The relapse of 367 disconnects the A.C. signal and 322 also operates 347 which holds the busy signal 302 already operated by 362. When the operator moves dial 282 off normal, 268, 272 operate in series, open the circuit of relays 274, 303 and on the relapse of 303, complete a ring circuit for 314, 310 in series, 310 remaining inert. The circuit for impulse-repeating relay 371 is now completed over the tips of J and P, keys 263, 280, impulse springs of 282 and over the sleeve circuit to ground at 311. Relay 371 operates relay 367 which holds itself and connects up the A.C. supply. During interdigital pauses these circuits revert to their pre-dialling condition. Incoming repeater, Figs. 4a, 4b, completion of connection. The A.C. seizing impulse operates relay 435 to complete an initial circuit for two-step relay 445 which operates fully on the relapse of 435 at the end of the impulse, grounds the release wire 26 and completes a loop circuit from relay 471 (lower) over repeating coil 437 and conductors 25, 27 to the incoming selector IS1, Fig. 5. Relay 471 remains inert and the holding ground operates 419, 400. The digits repeated by 371 as A.C. impulses are received by relay 435 which repeats them to 488. This relay opens the loop, holds dependent on 494 and operates 499 which energizes 494 to transfer the impulse circuit to 499 so that 499 is held during the impulse. The length of a repeated impulse is thus equal to the operating times of 499, 494 and the release period of 488. Slow-to-release relay 415 operated by 499 during a train shortcircuits the upper left-hand winding of coil 437 to improve the impulse-repeating circuits. Relay 400 is short-circuited by 499 during impulsing but not long enough to release. The connection is extended over incoming selector IS1 and connector C1 in known manner and, if the wanted party is free, the reversal of current by back bridge relay 602 operates 471 at the repeater and 473, 488 pull up in turn. Relay 473 shunts the impulse springs 493 to prevent the operation of 488 from opening the loop to the connector. Relay 488 operates 499, 494 in turn as before but 499 now operates 480 which locks up, shunts the impulse springs, releases 499, and short-circuits the lower windings of 494, 499 to make them slow-torelease. Relay 494 releases 488. The operation of 488 had energized 423 to connect A.C. to the junction to the operator'so that the duration of the A.C. pulse is equal to the combined operating times of 494, 499 and release time of 488. The A.C. pulse operates 320, Fig. 3, so that 343 pulls up in two steps and removes ground over 303 (lower) from the sleeve of J, thereby releasing 274, 278 in the operator's control circuit and extinguishing lamp 215. Relay 343 also prepares a circuit for shunting down 347 when 320 is operated by a long A.C. pulse (see next paragraph). The operator restores key K to release 200 which completes the speaking path and releases the control circuit PC. Release. When the called party hangs up, back bridge relay 602 restores normal battery conditions and 471, 473 fall back in turn. Since 480 is operated, the relapse of 473 operates 423 which connects A.C. to the junction. Relay 488, 499, 494 pull up in turn, 494 operates 461 (upper) which pulls up its light-locking contact and 488 falls back so that 499, 484 release slowly. The relapse of 494 allows 461 to operate fully and energizes 488 to start 488, 499, 494 on another cycle. The next operation of 494 energizes 458 which opens the looking circuits of 480, 461 but these relays together with 458 hold until 494 relapses. The release' of 480 thus terminates a long A.C. disconnect signal to the operator. The circuit of 488 is also opened to prevent further cycles of operation of 488, 499, 494, and the shunt around the impulse contacts 493 is removed. The long A.C. pulse temporarily releases 347 in the junction circuit, Fig. 3, so that 353 pulls up and releases 343 which grounds the sleeve of J to light lamps 215. When the operator disconnects, relays 322, 360, 347 fall back and 367 connects A.C. to the junction. When 360 relapses, the weighted armature vibrates for a time to hold 362, but eventually this relay slowly falls back 'to release 367 which disconnects the A.C. At the repeater, 435 is operated by the impulse and 488, 499, 494 start on a cycle, 499 and 494 holding to conductor 11 during the impulse. Relay 499 operates 415 and also connects ground from contact 433 of 430 to the lower end of 400 which is therefore shunted down and extends the shunt to 419 (during the long A.C. impulse 430 was operated to prevent this shunting). Relays 400, 419 fall back and 405, 410 pull up so that when 400, 419 reoperate at the end of the pulre 445 is released, opens the loop to the automatic switches which release in known manner, and removes ground from the release wire of the repeater. Relays 405, 410 also fall back. Wanted line busy, operator breaks in. Ground on the test-terminal operates busy relay 619 which connects up tone from 652 and locks when 627 relapses at the end of the last impulse train. Ring-tripping relay 615 operates and locks. The operator throws toll-offering key 286 which operates relays 268, 272 so that relays 274, 278, 303 in the sleeve circuit relapse and both relay 314 and marginal relay 310 in the ring circuit pull up. Relay 307 operated by ground on the jack springs operates relay 367 which connects up A.C. but 310 shortcircuits 307 which releases very slowly, owing to both the short-circuit and the slug, and disconnects the A.C. At the repeater, this signal has effects similar to that described at the end of the preceding paragraph, but it is not sufficiently long to allow 419 to fall back and operate 410, ground from 433 is therefore connected, when 400 reoperates at the end of the impulse, over conductor 21 and the upper speaking conductor to operate differential relay 600 at the connector. Switching relay 631 thereupon completes the speaking path, opens the busy-tone circuit, and holds busy relay 619 over the test-terminal. The back-bridge feed relay 602 has been disconnected by 619 so that the cut-in occurs without noise in the busy subscriber's receiver. The length of the ground pulse over the upper speaking conductor is determined by the release periods of 415 and 407. The busy party now hangs up his receiver, busy relay 619 falls back, grounds the test-wiper and connects up the back-bridge relay 602. When he again removes his receiver, the operator is signalled as described in a previous paragraph. Call from exchange A to manual; metering. The calling subscriber T1, Fig. 5, is connected by line-switch LS1 to selector 81 which in response to digit 0 seizes a repeater such as Figs. 4a, 4b terminating an idle junction to the manual exchange. The repeater is seized over conductors 24, 28 and relay 466 operated over the calling loop energizes 468. Relay 426 thereupon pulls up, grounds release conductor 6 and energizes 400, 419, and 410 which is slow-to-operate and energizes 423 to connect A.C. to the outgoing junction. Relay 410 also operates 405 which locks up while 410 slowly releases to terminate the A.C. signal by releasing 423. The A.C. impulse operates