Patent GB-472280-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1936-03-20
Abstract: 472,280. Automatic exchange systems. POLLAK, J. E. (Associated Electric Laboratories, Inc.) March 20, 1936, No. 8400. [Class 40 (iv)] In a, 400-line exchange using finder-connector links without a group-selecting stage, twodirectional finder switches have four sets of wipers and are arranged in two groups A and B controlled by separate allotters and normally serving corresponding 200-line subgroups of subscriber's lines with simultaneous bunting by one pair of wiper-sets during the rotary movement. Each group is however also capable of extending calls from the other sub-group of lines and in this case the second pair of wiper-sets is substituted. Separate groups of common start-leads are provided for each sub-group of lines, a group being connected to the vertical marking banks of the appropriate group of finders to control the vertical motion as soon as a call occurs. The connectors are also two-directional switches with four sets of wipers, wiper-selection being made by a vertical movement in response to a preliminary digit followed by return to normal. The switches employed are arranged with their shafts horizontal, the two switches of a link being arranged on a common base with their relays between them as described in Specification 472,295. Finder. Relay 107 operates partially, connecting ground over leads 119, 413 to relay 404 which operates, followed by relays 401, 407, 409. Relay 401 connects the start leads to the vertical bank 28 and relay 407 operates the start relay 146 of the allotted finder. Vertical magnet 145 and relay 408 now interact over leads 459, 460 to step the switch until the marked level is reached when relay 410 operates over lead 458 and wiper 29 to switch over from lead 459 to 462 so that rotary hunting takes place in a similar manner. When the calling line is found, one of the polarized test relays 141, 142 operates in series with 107 which then pulls up completely. Allotting arrangements. The test relay connects ground on lead 462 to lead 455 to operate the allotter magnet 465 which opens the circuit of relay 407, releasing 146. A self-interrupting circuit for magnet 465 is then completed over front contacts 427 of normally-energized relay 406 to ground on lead 455 in busy finders. Relay 406 is energized over lead 461 to ground at 297 in idle links. When the last link is taken into use relay 406 falls back as soon as 407 releases so that a further call in the A group starts, over leads 573, a finder in the B group. Relay 505 operates relay 402 to connect the A-group start leads to the vertical marking banks of the B-group finders and completes a circuit over lead 557 for a relay similar to relay 140 for switching over to the other two sets of wipers. When all finders of both groups are busy, and a further call is made in group A, say, relay 403 operates from ground on lead 413 over back contacts of relays 406, 506 and leads 573, 572 to connect busy tone to all non-engaged subscriber's lines. Connector. Relays 204, 206, 208, 213, 212 operate and impulses are repeated to vertical magnet 214 in parallel with relay 302. If the first digit is 3 or 4, on the relapse of 302 wiperswitching relay 303 or 304 operates over vertical wiper 329 and completes a circuit for the release magnet 215. When release is complete relay 210 operates in series with the release magnet and locks independently thereof disconnecting the magnet. If the first digit is 5, both relays 303, 304 operate. If the first digit is 2, neither wiper-switching relay operates, but relay 211 energizes over wiper 329, and effects the operation of the release magnet and relay 210, after which 211 is released. The second digit is also repeated to the vertical magnet and on the relapse of 302 relays 213, 212 release so that the third digit passes to the rotary magnet 343 in parallel with relay 302. During the digit relay 305 energizes and at the end of the digit, relay 306 energizes in series with 305, which it then disconnects, and directs the final (party-line) digit to magnet 327 of the minor switch 350.. 352. Relays 302, 305 again operate during this digit and at the end of the digit on the relapse of 302 the test relay 209 is connected over wiper 352 to the test wiper. Called line busy ; release. Relay 209 'operates and locks on the relapse of 305 connecting up busy tone. When the calling party hangs up, the release of relays 204, 206, 208 completes parallel circuits from ground 297 for the release magnets 215, 344 of the connector and minor switch. When off-normal contacts ON2 restore the ground is extended over lead 174 to the release magnet 143 of the finder. Called line idle ; party-line ringing. Relay 211 operates on the relapse of 305 and energizes relay 301 which connects up ringing-current. Frequency selection is effected by wiper 350 and the current is applied to one or other side of the line according to the condition of relay 306 which for final digits 1 to 5 releases on the operation of relay 211 but for digits 6 to 0 is held over wiper 351. When the called party replies, relays 213, 212, 203 operate. Reverting call. The ordinary directory number is called and the calling subscriber hangs up for a short interval on getting busy tone. Relays 204, 206 fall back but ground over the circuit 234, 247, 253, 352, 105, 118, 172 holds up relays 141, 107, 208. Relays 202, 211, 301, operate to connect up ringing current as before and on the removal of the receiver by either party relays 213, 203 operate, the latter acting as feed relay for both parties. Relay 207 operates to hold the connection in place of relay 208 which is released. Outgoing calls. Junctions to a manual exchange are connected to the banks of the normally-connected wipers 330, 332, 333 and are reached by dialling a four-figure number having a first digit 2 in the same way as calls to local subscribers. If the first junction of the group is busy, the test relay 209 operates relay 301 over the auxiliary pin-bank 26 and the rotary magnet 343 interacts with relay 301 to select an idle junction. Ringing current is then sent over the junction as in a local call. Junctions to automatic exchanges are connected in the ninth level of the normallyconnected wipers and are reached by dialling two digits 91. At the end of the first digit relay 210 is operated over wiper 329, and springs 354, 355 are closed so that at the end of the second digit the test relay 209 is connected over springs 354 to the test wiper. Hunting takes place as for a junction to a manual exchange but relay 201 operates partially over springs 355 at the beginning of hunting and fully at the end to connect the leads 170, 171 directly to an outgoing repeater. Further groups of ring-down trunks, e.g. to toll operators, reached by 3-digit numbers could be connected to the sixth, seventh, eighth or tenth level. Irregular operation. (i) Relays 409, 412 energized during the vertical and rotary movements, respectively, of the finder, connect up relay 411 over vibratory armatures. Normally relay 411 is unable to energize but, if undue delay occurs, it energizes to connect up an alarm, to release relay 406 to switch over to the other group, and to advance the allotter one step so that if the faulty group is taken into use again due to all the other groups becoming busy, a new finder will be used. Keys K1, K2 provide for busying a finder or an allotter. (ii) If no impulses are received by the connector, cam 284 operates relay 205 to connect up cam 285 which subsequently connects booster battery to test wire 172 to operate lock-out relay 106 and release the link. (iii) If the link fuse blows, the lower winding of relay 205 is operated and the link released as before. (iv) If a single impulse is dialled, a circuit is completed over vertical wiper 329 for the release magnet 215 to restore the switch to normal.