Patent GB-287079-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/42
Filed: 1928-01-12
Abstract: 287,079. Associated Telephone & Telegraph Co., (Assignees of Stehlik, R. F.). March 14, 1927, [Convention date]. Semi-automatic exchange systems.-A system in which subscribers at an automatic office are extended by the first selectors to junctions terminating at a manual office in cord circuits, which have previously been associated with register sets for controlling a number indicator, has the following features :-(1) The terminals of the switches C', which pre-select the register sets and which are straight multipled, are divided into groups in which the register sets appear in different orders so that if several switches having their wipers in different groups are associated with the same set, and that set becomes busy, they will then select different sets. The multipling and jumpering for this feature is effected in a readily alterable manner at a frame IDF having 25 sets of terminals on one side connected to the terminals of the switches, the terminals on the other side being connected to the register sets. In the system described 8 register sets are provided, one being artificially busied until the other 7 are in use. (2) A slow-to-operate relay 104 connected to the lower wire of the junction at the outgoing end marks it busy when ground is connected to the wire at the other end. This is done directly when the junctionrelay group is being tested, or when the main fuse 273 blows, by relay 200 which also disconnects the junction from the cord circuit. At other times, e.g. when relay ATB pulls up because all the registers but one are busy, when a key such as TK is thrown for busying a group of 8 junctions from different offices, when the switch C<1> is hunting, or after the calling party has hung up but before the manual connection has been broken down, ground for operating relay 104 is connected to the junction over the lower winding of the line relay 206 which remains unaffected. (3) The hunting switches C<1> are controlled by a relay 203 which cuts in an opposing winding to make itself quick-to-release. (4) Mutilated calls are displayed after a time interval in the same way as ordinary calls and extended to a special operator. (5) The junction is marked busy while the corresponding switch C<1> is hunting, but if it is seized before the busy mark is applied and the subscriber dials, he gets a busy signal. Some of these features are claimed in Specifications 296,069 and 296,070. Preselecting arrangements. A register set is seized, by connecting ground to the wire 301 and if any other switch C<1>, associated with an idle junction, is standing on this set, its control relay 203 completes a self-interrupting circuit for its magnet 320, cuts in an opposing winding, locks up to ground received from the busy sets passed over, and causes relay 104 at the outgoing end to mark the junction busy. If a subscriber is already connected to the cord and dials before a register set is picked up, relay 202 pulls up and gives a busy tone. The reserve (8th) set has its terminals 379, 381 connected to terminals 383. 382 instead of strapped together, and has the armature 340 connected to 388 instead of 387. It is thus normally marked busy at 396 but becomes selectable when, owing to the operation of the relays 325 of all the other sets, relay 392 falls back. When it is seized, relay 391 falls back and energizes relay 393 which causes any other switches that may be hunting to stop on the blank terminals provided at the end of each group. The relays 392 on falling back also energizes relay ATB to cause all the junctions on the position to be marked busy. Displaying wanted number. The calling party in response to the first digit is connected to a repeater E of which the line relay 101 energizes the line relay 206 of the distant cord circuit over one wire of the junction. An instant later. 104 which is energized by the repeater release relay 102, opens the above circuit and bridges the junction, and 206, the lower winding of which is connected up by the cord circuit release relay 205, is then held by the bridge. Relay 204 pulls up in series with relay 325 in the preselected register set, locks up, marks the register set busy and connects up the impulsing wire 303 over which, and wiper 355 of a sequence switch RCS, the remaining digits are repeated in turn to registers R1 - - R4. After all four digits have been received, the switch RCS energizes 326 which lights a pilot lamp 370 to show which register set has taken the call, energizes relay 281 to start the " consecution switch CCS and removes ground which normally short-circuits relay 329 from wire 376 to mark the register set in its bank. On reaching the marked terminal the switch stops and energizes relay 329 which lights the call-indicator lamps and energizes 211 in series with the lamp CL in the cord circuit. Wanted line busy. Operation of busy key BK energizes the backstroke magnet of switch CCS and relay 202, 209 being operated in parallel with 211 which sends back busy tone and releases 204 which ungrounds wire 301 to remove a short circuit from 324 which pulls up over a contact of off-normal relay 323 and energizes the release magnets of all the switches in series with 322 Relay 322 marks the register set busy while any switch is off-normal. Relay 323 is short-circuited by relay 324 and falls back sluggishly followed by 324, 325. When the key is released, the switch CCS moves on. Wanted line idle. On insertion of the plug P, sleeve relay 210 pulls up in series with cut-off re.lay 261, completes ringing and ring-back circuits, puts out lamps CL and energizes relay 201 which locks up, unlocks relay 204 ungrounds wire 301 to release the register set and prepares an interrupter circuit for lamp CL which is com pleted if the plug is withdawn prematurely. When the called party answers, relay 912 energizes switching relay 213 which locks up. Back-bridge relay 208 energizes reversing relay 207 (provided the call has not been abandoned) whereupon relay 105 energizes reversing relay 100. Release. Relapse of 101 energizes 103 which temporarily unguards the repeater to release the selectors. On the relapse of 103 following that of 102 the guard is replaced, 104 remaining energized over the lower junction wire and lower winding of relay 206, until the connection is taken down in response to the glowing of lamps SL. Mutilated calls. Relay 325, when the register set is seized, connects magnet 365 of a timing switch P to a one second interrupter T. Each time relay 328 pulls up in response to dialling, the switch is released, but if it reaches its last terminals, relay 326 is energized to cause the operation of switch CCS and display of the number as far as it has been set up. Such calls are plugged into J' and relay 266 lights a lamp L in front of a special operator. Sleeve relay 210 pulls up as in an ordinary call, but in this case the ringing cut-off relay 212 pulls up at once over the secondary coil 1C from which the subscriber receives interrupted ringing tone. When the operator throws key AK to answer the call, relay 265 extinguishes the lamp, locks up, and cuts off the tone coil. Night-working. The right and left hand halves respectively of positions 3, 1 are busied by means of the keys TK. and the keys POS1, POS2, are thrown at positions 1, 2 to link the headset at position 2 with the cords at the adjacent positions. Testing. Connection is made for testing purposes by means of a jack at the left hand side of the cord circuit, relay 200 disconnects the incoming junction and causes it to be marked busy. When a test plug is inserted in the jack at the left hand side of the register set relay 921 marks it busy, disconnects relay 329 to present display of any number set up, and disconnects the pilot lamp 370. Both kinds of test can be performed without disturbing the operator.