Patent GB-696571-A (GB)
Title: Automatic telephone system
IPC: H04Q3/00
Filed: 1948-05-18
Abstract: 696,571. Automatic exchange systems. AUTOMATIC ELECTRIC LABORATORIES, Inc. May 18,1948 [May 28, 1947], No. 13432/48. Class 40 (iv). A Strowger system comprises a satellite exchange having discriminating selector-repeaters and a main exchange. The lines are formed in groups each consisting of two subgroups of one hundred lines. Two groups of finder-first selector links are allotted to each group of lines and each sub-group appears in levels 1-5 of one group of finders and in levels 6-10 of the other, preference being given to the levels 1-5. Subscriber A, Fig. 1, in the main exchange calls a subscriber in the same exchange. The associated groups of finders will be termed first and second groups and it is assumed that the subscriber A is connected to levels 1 and 6 of the first and second groups respectively. The line relay 110 earths level 1 of the vertical banks 250 of the first group of finders and energizes the start relay 445 of the control circuit, Fig. 4a, of the associated first group of finder-selector links, Figs. 2, 5. Relay 420 applies starting earth to a timing circuit 438. Relay 450 operates to earth level 5 of the vertical contact banks of the first group of finders to limit the search to the lower five levels, and the start relay 200 of the line finderfirst selector link pre-assigned by the first group allotter switch, Fig. 3, follows to connect up the finder switching circuit and to close an outgoing loop, thus operating the line and hold relays 500, 510 of the first selector. Under the control of a step relay 415 the vertical magnet 240 steps the shaft wiper 253 in search of the marked level, i.e. 1. Relays 425, 430 pull up and by interaction of the step relay 415 and the rotary magnet 245 the finder-wipers are rotated into their contact bank. When the calling line is found, cut-off relay 120 and a marginal test relay 465 energize in series and relay 220 or 230 operates (according to whether wipers 261, 263, 265 or 262, 264, 266 are connected to the calling line), and the caller is switched through to the first selector from which dialling tone is reverted. Line relay 110 releases, removes the marking from level 1 and opens the circuit of the start relay 445. The operation of relay 220 shunts down 450 and providing there is an idle link in the first group, completes a circuit for the allotter switch magnet 300 which steps by selfinterruption until an idle link is found. The control circuit returns to normal and the finder start relay 200 falls back. Should all the first group of links be busy, on the release of relay 450, relay 440, normally operated over a circuit multipled to the vertical off-normal springs of the first group of finders, falls back to prevent earth being connected to level 5 of the vertical banks 250<SP>1</SP> of the second group of finders, and to disconnect the start relay 445. When another call occurs in the first group and providing relay 440<SP>1</SP> of the control circuit, Fig. 4b, of the second group of links is operated indicating an idle second group link, start relay 4451 operates and the pre-assigned second group finder searches for the marked level in the upper five levels of the vertical bank 250<SP>1</SP>. If a first group finder when searching fails to find a marked level or to find the calling line in the marked level, its wipers are rotated either by the earth connected to level 5 or by the marking earth to the eleventh position, whereon spring set 237 closes a circuit for relay 460. Relay 230 operates and the allotter switch hunts for an idle link and disconnects relays 200, 230; the release magnet 255 is energized and the finderselector link and the control circuit are released. If, through a fault, the control circuit is held too long, the timing circuit 438 prepared by relay 420 connects an earth pulse to conductor 418 and relay 405 pulls up and, on a succeeding pulse being sent over conductor 419, relay 410 operates. Should a second group link be available, relay 400 connects up an alarm supervisory circuit and releases 440 so that subsequent calls are dealt with by the second group control circuit, Fig. 4B, until the attendant throws the reset key 404 to release 400, 410. Should all the second group links be busy, i.e. 4401 released, relay 410 is held long enough to allow the allotter to step to another idle link and is then released, whereupon 440 reoperates. First selector, Fig. 5. The first digit impulses line relay 500, the switch is stepped vertically by magnet 560, and dialling relay 540 and a step relay 530 operate. At the end of the digit, the release of 540 connects up the rotary magnet 565, which interacts with the step relay 530. Should there be no idle outlet in the selected level, at the eleventh position spring set 507 operates and busy tone is reverted. When an idle outlet is found, relay 550 switches through. Second selector, Fig. 6. When the selector is seized relay 620 pulls up. In response to the second digit relay 500 transmits impulses to line relay 600 for stepping the vertical magnet 640 and dialling relay 540 breaks the calling loop. Relay 610 applies earth to a traffic meter. At the end of the digit relays 540, 620 release and relay 600 acting as a step relay controls the stepping of the rotary magnet 650. If no idle outlet is found, cam spring set 645 closes to revert busy tone, but if the hunting is successful, relay 630 switches through and 610 releases. Connector, Fig. 7. The third digit sets a third selector 780, similar to the second selector, which switches through to a connector and relays 710, 720 pull up. In response to the fourth digit, the line relay 500 pulses relay 700 to step the vertical magnet 770, and the subsequent release of 720 operates relay 760 and connects up the rotary magnet 775. Relay 720 re-operates for the duration of the fifth digit, and the called station is tested during the slow-release of relay 760. If busy, busy tone is connected to the calling line by the release of relay 760. If idle, relay 730 pulls up to transmit continuous ringing current until the release of relay 760 connects up intermittent ringing current, ringing tone being sent to the caller through condenser 739. When the called party answers, relays 740, 750 operate and the call is switched through. P.B.X. connector, Fig. 8. Each except the last of a group of P.B.X. lines is provided with a fourth wire EC, Fig. 13, earthed when either the line relay 110<SP>1</SP> or cut-off relay 120<SP>1</SP> is operated, and a P.B.X. connector, Fig. 8, has a corresponding fourth wiper 889. The connector responds to the fourth digit as described above, and at the end of the digit relay 870 disconnects the vertical magnet 870 and connects up the rotary magnet 875. Relays 820, 860 pull up and the impulses of the fifth digit are repeated by relay 500 to relay 800 which steps the wipers to the first line of the wanted group. Dialling relays 540, 820 release and the circuit of slowrelease relay 890 is broken. If the first line is busy earth from the wire EC holds relay 890 and operates 800 to step the wipers to the next line. If all the lines are busy, when the wipers reach the last line relay 890 falls back and 860 follows to revert busy tone. Should an idle line be found, 890 releases and relay 830 operates in series with the cut-off relay of the called line, and the caller is rung. Subscriber C in satellite exchange calls subscriber 501, 599 in same exchange. An idle line finder link comprising a line finder 1108, Fig. 11, connected in parallel to a discriminating selector 1227 ... 1229 and a junction hunter 1237 ... 1239, Fig. 12, is seized, the junction hunter being assumed to be resting on an idle outlet leading to the main exchange. The discriminating selector has a vertical contact bank 1138 swept by a shaft wiper 1139. Line relay 1100 operates over the calling loop and 1110 follows. Relay 1230 seizes the outgoing junction circuit, Fig. 13, and 1210 switches through to this circuit and energizes 1130 which pulls up and transmits dialling tone to the caller. The impulses of the first digit 5 are repeated by relay 1100 to the vertical magnet 1260, and when the selector wipers are raised to the fifth level a right post spring set 1147 is operated, completing at the end of the digit on the release of 1230 and dialling relay 1240 a circuit for the release magnet 1275. The release magnet returns the selector by gravity to normal and connects the two opposed windings of relay 1140 in parallel. The release of magnet 1275 momentarily causes an operating current to pass through the windings of 1140 in series and 1140 locks up. Relay 1230 re-operates. In response to the second digit 0, the selector wipers are raised to the tenth level causing a left post spring set 1148 to operate. The release magnet 1275 is energized, the selector is again returned to normal, and relay 1150 is operated and locked in a manner similar to 1140 to de-energize 1210 and thus to free the junction circuit. At the end of the third digit 1, the release of relays 1230, 1240 connects up relay 1160, and the selector hunts under the control of the rotary magnet 1265 and a step relay 1220 for an idle second selector, Fig. 6, and when successful relay 1250 switches through the line wires. The remaining digits are repeated by relay 1100 to the line relays of the second selector and connector, and the call is completed as described above. Subscriber C in satellite exchange calls subscriber 53999 in main exchange. Relays 1100, 1110, 1230 operate as described above. Should the junction hunter be connected to a busy idle junction, magnet 1270 under the control of a step relay 1220 steps the hunter to an idle junction, whereupon the operation of relay 1210 opens the magnet circuit and switches through. Relay 1330 is normally energized over the line loop closed in the incoming first selector, Fig. 14, in the main exchange. Relay 1310 pulls up to remove an