Patent GB-301495-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04M3/60
Filed: 1928-11-12
Abstract: 301,495. Associated Telephone & Telegraph Co., (Assignees of Ruggles, L. L.). Dec. 2, 1927, [Convention date]. Semi - automatic exchange and party line systems.-In a system resembling that described in Specification 292,498, in which interconnections in a rural office of up to 80 party lines are controlled by a distant operation, connections are initiated by transmitting magneto current over one line wire and are released by breaking the loop. The finder switch that normally associates the operating trunk with a calling connector, in response to the transmission by the operator of alternating current over the trunk or to the occurrence of a fault or an " all connectors busy " condition, associates the trunk with a supervisory switch SS over which the operator can, on the first 8 levels, make connection to subscribers, on the 9th listen to the connectors in turn and release silent ones, and on the 10th ascertatin the nature of a fault. The operator can restore a connector she has set wrongly without breaking the connection with the calling line by operating a key which controls a differential relay at the rural end of the operating trunk. This relay, when the operator is making connection to a subscriber over the supervisory switch, controls the ringing circuit and thus enables her to send the desired code by repeated operation of the key. Control of connector by operator. A call is initiated by depressing a push P and operating the magneto to energize line relay 302, which locks up temporarily over off-normal springs of the plunger-type line switch and energizes the pull-down winding 304. The holding winding 305 is energized in series with 321, which locks up, marks the connector calling over 276, and energizes magnet 208 which interacts with a relay 201 to drive the finder. When the connector is found, 202 cuts the drive, extends the talking circuit and bridges the operating trunk by relays 203, 204, to energize 103 at the distant end and light a calling lamp. 204, 205, 206 pull up to cause 202 to be held locally. The operator momentarily throws her answering key ANS, energizing 102, 106, which lock up and light a busy lamp. 102 replaces 103 by the dial springs CD, and 106 extends a talking circuit to the operator, who then dials the wanted number. The first two digits are repeated by 204 over 275 to the magnets 333, 334 of the connector, which tests the line in the usual way. Code ringing automatically. Test relay 325 extends the impulsing circuit to the magnet 341 of a switch CS, which, in response to the third digit, picks out a code ringing wire. Rotary dialling relay 324, which is re-energized during this digit, falls back at the end and energizes the (busy) relay 323 over off-normal contacts of the code-switch to connect 326 to the pick-up wire PU. At the beginning of the next cycle, 326 completes the ringing circuit and locks up, and at the end 327 cuts off the ringing current and completes the connection. Disconnection of operator. Waiting calls. After dialling the number, the operator momentarily throws RK which, provided 101, which is sluggish and is energized over off-normal springs of the dial, has fallen back, energizes 104, which disconnects both wires of the operating trunk and energizes 105. 105 holds 104 independently of the key, unlocks 102, 106, and falls sluggishly on the relapse of the latter. At the rural end, 204, 205. 202. 206 fall back. If there is a waiting call, the finder magnet is energized by the relapse of 202, the relapse of 206 being delayed long enough to prevent 202 'from remaining energized if the connector just used is still marked calling, and not enough to prevent the re-operation should the next connector be calling. Release. The connector is held by relay 320, which is held over both loops in parallel, until both subscribers hang up, but talking condensers could be inserted on the called side. The relapse of 320 releases the line switch which releases 321 to operate the release magnets 332, 340 and release the connector relays, except 323, which waits for the code switch to reach normal. Cancelling wrong setting. When the operator throws SRK, the differential relay 203 energizes the release magnets 332, 340, over 274. The former unlocks any operated relays except 320, which is holding the line switch, and 321. Release of trunk circuit without dialling. The operator throws RK, energizing 104 to release the trunk circuit as described above. Magnet 333 thus receives an impulse and springs 328 change over to give the subscriber power to release the connector. Signalling all connectors busy " to operator. When the last connector goes off-normal, 368 falls back to prevent useless operation of the master switch, and when it has been completely set, 326 removes the last ground from 277, releasing 232 to energize 234, which locks up, starts the finder and marks the supervisory. switch SS calling. When the operator replies, she hears a busy tone (provided. 232 is still back), and then dials 91. When the switch moves, off-normal relay 231 energizes 232 to take off the busy tone. The talking terminals in this level are connected to the talking wires of the connectors, and the operator moves the switch in single steps until she finds a silent one, whereupon she throws SRK to unbalance 203, which over 245 shunts out the holding relay 320. When the operator clears, the relapse of 206 releases 234 to energize the release magnet of the switch SS. Signalling faults to operator. The occurrence of a fault, e.g. the operation of a heat coil 255, energizes 233, which energizes 234 to cause the finder to pick up the switch SS and signal the operator, who hears a distinctive tone over contacts of 233. 234 also disconnects the common marking ground 278 to prevent interference by subscribers. The operator than dials the switch in single steps over the 10th level, and when she reaches the terminals of the operated heat coil &c., hears a tone current. Relays 251 associated with the alarm devices are energized over wiper 244, and that of the operated one locks up until the fault is cleared and prevents this fault,from recalling the operator after she has cleared. Operation of switch SS to call subscribers. Code ringing manually. The operator 'over key RGK sends ringing current over the operating- trunk, energizing 234, which locks up and energizes 233. The swich SS is thus associated with the operating trunk as when a fault occurs and the operator dials the number of the wanted line. She then operates the key SRK in accordance with the code of the wanted subscriber, and 203 follows the key and rings the line. 9th level springs 240 in the ringing circuit prevent the application of ringing current when 203 is operated to release a silent connector as described above.