Patent GB-666500-A (GB)
Title: Automatic exchange systems
IPC: H04Q3/00
Filed: 1948-11-15
Abstract: 666,500. Automatic exchange systems. AUTOMATIC ELECTRIC LABORATORIES, Inc. Nov. 15, 1948 [Dec. 30, 1947], No. 29619/49. Class 40 (iv). An automatic telephone system has two groups of two-party lines, each group terminating in a different bank of a single-motion connector having two sets of wipers, and second parties in either group are selectively rung in response to the wiper's stopping in a certain position, the operation of the wipers being controlled by incoming digits. The embodiment described is a P.A.X. with facilities for code calls to parties absent from their stations, for breaking in by privileged subscribers, and for special alarms. Local call. The call allotter is of the preselecting type and relays such as 150, 150<SP>1</SP> of idle links are already operated when a call is initiated. When a subscriber H in the first group of lines removes his receiver he completes an operating circuit for relays 110, 170 in series. Line and cut-off relay 110 operates through its first step, applying marking battery to control conductor 188, while relay 170 completes an all-link-busy test circuit and brings up line relay 120, followed by hold relay 130. This completes a circuit over wiper 196 for motor magnet 180 which steps its wipers 191- 198 anti-clockwise until they reach the calling line, where wiper 195 encounters the battery potential on control conductor 188. Relay 140 operates and locks, connecting the calling line loop to relay 120 and a source of dialling tone, operating relay 110 through its second step to release relay 170, and releasing relay 150 to prepare a starting circuit for the next idle link. On receiving dialling tone, the calling party H dials the wanted number, say " 271 " corresponding to the first party J on a line of the second group. Line relay 120 follows the first digit " 2 " and causes motor magnet 280 to step its wipers 232-239 to their second contacts, whereupon wiper-switching relay 240 operates over wiper 236 and locks, switching the connections from the first to the second set of wipers, giving access to the second line group. The second digit " 7 " and third digit " 1 " move the wipers a further 8 steps to their tenth contacts, terminating the called line. Slowreleasing relay 270 is energized during the impulsing and prepares a busy test. If the called line is engaged, busy relay 250 operates to earth over wiper 237, but if it is free, battery on wiper 237 operates relay 220 which locks and applies ringing current and busying earth to the called line. In answering J shunts his bell and applies direct earth to relay 210 which locks and completes the connection. When the parties hang up, all the equipment is released, motor magnet 280 homing over wiper 239. The call number of the second party J<SP>1</SP> on J's line is " 1171 " so that the connector wipers 232-239 stop at their second, ninth and tenth contacts as before but also stop at their first contacts, where relay 200 operates over wiper 236 and reverses the ringing current. All second parties have call numbers whose first digit is " 1 " and all subscribers in the second line group have numbers beginning with " 2 " or " 11." Breaking-in be privileged subscriber. On receiving busy tone, a privileged subscriber may depress a key 185 to operate a relay 260, which locks to earth on the busy line encountered by wiper 237, disconnects busy tone, releases relay 250, and joins the caller to the existing connection. He may request the wanted party to hang up, which removes the earth from control conductor 175 so that relay 260 releases. Ringing relay 220 then operates and the call proceeds as above. Code call to a party absent from his station. To call a party who is known to be somewhere in the area served by the P.A.X., the code call initiating digit " 3 " is dialled. The finderconnector link, Figs. 1 and 2, operates as before, motor magnet 280 stepping its wipers 232-239 to their third contacts. Relays 220, 300 are then energized in series over wiper 236 and bring up line relay 305 followed by hold relay 310, which busies the code call finder and completes a circuit for motor magnet 380 which interacts with relay 360 to step its wipers 395-398 until they reach the calling line. Here wiper 398 encounters the earth placed on extra control conductor 124 over wiper 238, and relays 260, 350, 360 are energized in series. Relay 260 initiates release of the finder-connector link while relay 350 locks, busies the calling line and extends it into the code call equipment, Figs. 3 and 4, shunts and releases relay 360, disconnects motor magnet 380, and releases relay 300. Line relay 305 holds over the calling line loop, and the caller again receives dialling tone, whereupon he dials the code call number, say " 22," of the wanted subscriber. Line relay 305 follows the first digit " 2 " and causes motor magnet 413 to step its wipers 486-489 to their second contacts, whereupon a storage relay 460 operates over wiper 488, preparing paths for marking contacts of wiper 486 and bringing up relay 330 which locks, removes dialling tone, and completes a circuit over wiper 487 to motor magnet 43, which restores wipers 486-489 to normal whereupon relay 330 releases. Storage relay 460 holds in series with relay 440 which operates to switch the connections from the first set of storage relays 450, 460, 470 to the second set 480, 490, 475. The second-digit " 2 " produces similar results to the first and ends with relays 420, 490 energized in series. Slow-operating relays 345, 340 now interact, relay 340 being also slow-releasing, and cause motor magnet 413 to step its wipers 486-489. At each step a burst of tone is sent over the calling line and relay 365 is operated to ring code sounders such as 390, 391. After two steps wiper 486 encounters the marking earth corresponding to the first digit " 2 " of the code call number, made effective through the operation of relays 420, 460. Relay 330 operates, and motor magnet 413 homes over wiper 487 as before, whereupon relay 330 releases. This opens a circuit containing the two windings of relay 415 in opposition and the resulting inductive surge of current causes relay 415 to operate through its first step, closing contacts 418. The two windings are now series-aiding and relay 415 operates through its second step, bringing up relay 430 to give effect to the marking corresponding to the second digit " 2 " of the code call number. Relays 345, 340 have continued to interact and the code sounders signal the second digit as they did the first. Relay 400 then operates similarly to relay 415, switches the marking earth to the third contact of wiper 486, and opens the circuit of relay 365 to prevent operation of the code sounders. The interaction of relays 345, 340 continues and motor magnet 413 steps its wipers 486-489 until they reach their third contacts, where relay 330 reoperates, bringing up a slow-releasing relay 385 which releases relays 400, 415 and restores after the release of relay 330 by the homing of motor magnet 413. This ends the first code ringing cycle. Further identical cycles continue until the call is answered or the caller hangs up. The called subscriber answers by removing the nearest receiver and dialling the code call answering number " 906." The finder-connector link operates as usual, the connector wipers being stepped to their twenty-fifth contacts. Relay 220 operates over wiper 236 to battery on conductor 304 and energizes relays 210, 320 in series over conductors 302, 303 and wipers 232, 234. Relay 320 completes the talking connection and opens one circuit to relay 345, whose other circuit is opened when relay 400 operates during the code ringing cycle, thus preventing further ringing. The equipment is released when the parties hang up, lastparty release being provided by the presence of two holding earths for hold relay 310, one controlled by each party. Special alarm. A key 328 is depressed to energize a relay 370, which starts relays 345, 340 interacting to operate relay 365 and ring the code sounders as before but without stepping wipers 486-489. If the code call equipment is already in use, relay 370 brings up relay 330 and motor magnet 713 homes as before, the alarm then continuing as above. When the key 328 is released, relay 370 restores and the code call continues normally.