Patent GB-228287-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/62
Filed: 1923-12-10
Abstract: 228,287. Coventry Automatic Telephones, Ltd., and Collyer, J. E. Dec. 10, 1923. Automatic exchange systems.- Two or three-digit private exchanges are provided with connectors or group selectors of rotary type in which the terminals are divided into groups corresponding to the first digits. The switches are stepped by the first dialled digit and then automatically to a position depending on that digit, and afterwards hunt for an idle line or pause and are stepped into the group by a further digit. In the case of connectors, provision is made for selecting an idle exchange line. Means are provided for giving a signal if a non-existant number is dialled. A Strowger connector is described in which the change-over relay is made sluggish by a normally short-circuited winding and is used also as a switching relay. Two-digit system; call-finder. A call over the line 4, 5, energizes line relay 1 and common relay 7. Relay 7 grounds all the idle test terminals and energizes relay 11 which starts up one or more 25- point reverse-drive call-finders such as B. When the line is found, switching relay 19 being no longer short-circuited pulls up and energizes cut-off relay 2 and connector line relay 102. Relays 1, 7, 11 fall back. Connector for 24 lines numbered 11 - - 34. The connector has a normal and 25 working sets of terminals and two sets of wipers 180‹ apart. The energization of relay 102 is followed by that of release relay 104 and relays 107, 117. The first digit is repeated by relay 102 to stepping magnet 109. The change-over of off-normal contact 101 arranges for the release of relay 107 at the end of the digit. If the digit is 1, the switch conies to rest, but if 2 relay 154 pulls up over control wiper 115 and locks itself and if 3 relay 161 pulls up in a similar circuit,. energizes relay 154 and locks up. The energizing circuit of relays 154, 161 goes over the stepping magnet which does not energize in this circuit. Relay 154, however, short-circuits the energizing windings of relays 154, 161 and the stepping magnet then operates to drive the wipers on to terminal 160 or terminal 164 according as the digit is 2 or 3. At the beginning of the second digit, relay 117 falls back and relay 107 pulls up again, but does not re-energize relay 117 which is short-circuited. The wipers are stepped by the second digit to the wanted line and relay 107 then falls back slowly. Busy test. If the line is busy, relav 128 pulls up and on the relapse of relay 107 locks up and sends busy tone from 133. The busy generator is started over wire 136. Supply of ringing and talking currents. If relay 128 is unoperated the relapse of relay 107 energizes relay 139 in series with the wanted cut-off relay. Relay 139 locks up, starts the ringing generator over wire 144 and sends ringing current from 145 over relay 146. On the operation of ringing cut-off relay 146, relay 128, over which the called line is fed, pulls up but does not operate the busy signal which is disconnected at 138, 135. Non-existent numbers. If a first digit greater than 3 is dialled, the control wiper 115 moves on to permanently grounded terminals and the switch is stepped on to terminal 158 whereupon busy relay 128 pulls up in series with the stepping magnet and locks over its lower winding. If following a first digit 3 a digit greater than 4 is dialled, the wipers move off the bank and the second set comes into the normal position. The change-over of off-normal contact 101 prevents further stepping and busy relay 128 pulls up over wiper 114 and its lower winding and locks over its upper winding and wiper 115. Calls for main exchange. The last four terminals may be allotted to the main exchange ir. which case the control terminals are strapped to the test terminals. Exchange calls are made by dialling 01. The digit 0 operates relay 161 which causes the switch to step automatically to the first exchange line. The digit 1 is sent only to release relay 117 and is made ineffective on the magnet circuit by making relay 161 cut the impulse circuit when operated. Two-hundred line system with 25-point group selector. When a call-finder such as that shown in Fig. 1 comes to rest, line relay 201 of the group selector, Fig. 3, pulls up, followed by sluggish relays 203, 206. The first digit is repeated to stepping magnet 208 and at the end of the digit relay 206 falls back owing to the change over of off-normal contact 207, and energizes relay 219, or relay 235 over the control wiper 214 and stepping magnet according as the first digit is 1 or 2. Relay 235 if operated locks up over its upper winding and short-circuits its lower to allow the stepping magnet to operate and the switch is driven on to terminal 238 which is the first associated with the 2nd group of 100 subscribers. In this position relay 219 pulls up. In either case, relay 219 on energizing locks up and connects the test wiper 213 to the stepping magnet and the switching relay 126, and the selector hunts for an idle line. Operation of the switching relay 226 releases relays 201, 203. If all the lines are busy the wipers move on to 11th terminals such as 229, 230, relay 201 holds up over its lower winding and busy tone is sent out over 232. Strowger connector, Fig. 4. Energization of line relay 301 is followed bv that of release relay 303 and change-over relay 306. Vertical impulses are repeated to magnet 308. The change-over of off-normal contact 313 energizes relay 317 and arranges for the release of relay 306, the upper winding of which is short-circuited at this stage, at the end of the digit. Relay 306 on falling back switches over to the rotary magnet 307 and at the end of the digit, owing to the change-over of rotary springs 314, 315, relav 317 falls back. Busy test. If the wanted line is busy, relay 325 .pulls up, and on the relapse of 317 locks up and sends busy tone from 328. The busy generator is started over 344 by the release relay. Supply of ringing and talking currents. If the line is idle, the relapse of relay 317 energizes relay 306 which now acts as a switching relay and extends the c-wire to operate the wanted cut-off relay. Ringing current is sent from 332, the ring- ing generator having been started over the wire 344 by the release relay. Ringing cut-off relay 333 energizes as usual when the subscriber replies and. energizes relay 325 over which the called loop is fed. Relay 325 alters the circuit of relay 306 so that it receives current over both windings. Release. The relapse of relays 301, 303 when the calling party hangs up, energizes the release magnet 309 and ungrounds the c-wire to release all the relays holding to it. The relapse of relay 226, Fig. 3, completes a restoring circuit for magnet 208. Non-existant numbers. If a hundreds digit greater than 3 is dialled, a self-interrupting circuit over wiper 214 is made for the stepping magnet and the wipers advance until wiper 214 reaches terminal 239 in which position the other wipers are on their 11th terminals. Relay 219 now operates over 240, 239, 208, locks up and energizes relay 226 so that busy tone is sent back from 232.