Patent GB-289065-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/42
Filed: 1928-04-20
Abstract: 289,065. Associated Telephone & Telegraph Co., (Assignees of Stehlik, R. F.). April 22, 1927, [Convention date]. Automatic and semi-automatic exchange systems. - In systems comprising automatic and manual exchanges, the first digit of a manual exchange number dialled by an automatic subscriber operates an office selector to find an idle trunk to the required exchange terminating in a cord circuit at a B operator's position. In order to prevent mutilated or wrong numbers being displayed to the operator owing to the second digit being dialled before a register set is connected to the cord each cord is provided with a register RG on which each digit in turn is registered and then transferred to a register set connected thereto by a switch C<1>. Each manual trunk comprises a repeater E, and the second and further digits are repeated thereby and again by the cord circuit to operate RG. RG comprises five two-step relays so arranged that the energization of the later relays releases the earlier ones so that the later impulses of digits 6 - - 10 energize the five relays over again, and the relays energized by the different digits are shown in the chart on Fig. 3. Each register comprises four identical sets R<1> - - R<4> of four relays, one set for recording each digit of the number, the method of differentiating between digits being shown in the chart on Fig. 4. A switch CCS, Fig. 4, has its contacts connected to the registers and connects to the operated registers in turn to display the number on lamp panels. If switch C<1> has not found when the second digit is recorded on RG the busy relay in the cord will be energized to send back busy tone and stop the switch C<1> after the second digit is dialled. The repeaters E are busied if the operator removes his headset plug P<1>. Connection to cord circuit O, Fig. 2. When the automatic subscriber picks up his receiver his line relay selects an office selector which is operated by the first dialled digit to select a trunk leading to the required exchange, comprising the repeater E. Line and release relays 101, 102 of the repeater energize, and slow-to-energize relay 104 begins to pull up, during which line relay 202 of the cord-circuit O, Fig. 2 is operated [earth, 118, 113, 130, 214, 202, battery] and release relay 203 pulls up so that when 104 pulls up, 202 is held over both windings and a bridge 111, right-hand winding of impedance coil 106, 108, lower winding of polarized relay 105, 116, 118, 113. Relay 105 does not energize since a reverse current passes through its upper winding. Operation of register selector C', Fig. 3. A circuit is now closed from earth to 224 for switching relay 204 and magnet 350 in series. If C' is on a busy register, earth from the corresponding armature 226 shorts 204 over conductor 265 and C<1> steps on till an idle register is found, when 204 pulls up. Registration of second digit 3 at RG, Fig. 3. The impulses are repeated by line relays 101, 202 to conductors 260, 261. Slow-release relays 300, 301 energize over 261 and remain up throughout the digit. The first impulse passes to two-step relay 302, which fully energizes at the end of the impulse [earth, 309, 321, 311, 302, battery], and the next two impulses operate relays 303, 304, the latter releasing 302. Seizure of register and transfer of second digit. Relay 406, Fig. 4, energizes from earth at 226, energizing relay 400 of register R<1> to connect relays 401 - - 404 thereof to the transfer conductors 450 - - 453. Between the moments of release of 300, 301, relay 402 only of R<1> energizes [earth 263, 2'25, 262, 318, 333, 337, 452, 414, 402, batteryand locks up in series with relay 405. When 301 releases, RG returns to normal, and 405, previously shorted pulls up, releases 400 and energizes relay 500 to connect up register R<2>. Registration of remaining digits. The third digit 4 is registered on relays 302 - - 305, but the energization of 305 releases 302 as shown in the chart, and relays 502, 503 (not shown), curresponds to 402, 403 are energized as per chart. The fourth digit 5 is finally registered on 603 (not shown), and the fifth digit 6 on 701, 703 (not shown). The transfer relays 505, 605, energize in turn to switch the transfer conductors to registers R<3>, R<4> and 705 finally closes a circuit [earth 431, 716, relay 408, battery] to energize relay 408, lighting pilot lamp PL to notify the operator that a call is registered on the set. Start relay 409 of switch CCS now operates. Operation of switch CCS and indication of wanted number and the cord in use. Relays 408, 409 being energized as above, relay 411 will pull up, forming a circuit for relay 410 and magnet 449 in series. The contacts of switch CCS lead to different registers and if the wiper is on the contact of an idle register, earth from an armature such as 437 shoots 410, and the switch steps to a completely charged register-set, say that shown, Relay 410 pulls up and cuts the circuit of line relay 411, during the release of which relay 407 energizes and locks to earth at 432, to which 410 also locks. Armature 433 is now operated to light the lamps in the various sets in accordance with the setting of the registers. Earth at 434 operates call lamp CL and relays 208, 205 in the cord, and the operator then tests the wanted subscriber's jack J with the plug P. Wanted subscriber busy. Operator presses busy key K, operating busy relay 210 which locks up, applies busy tone from BT to conductor 130, and releases relay 204. Earth is removed from 265 to release 406, 407, 410 in turn, and also the register sets and 408. Relay 409 therefore releases and the contact 447 of switch CCS is again earthed. Wanted subscriber idle. On plugging in, sleeve relay 211 operates in series with his cutoff relay 250, relay 206 is then energized and the operator's head-set disconnected. Relays 208, 205, and lamp CL are released by 206, and relay 207 energizes over conductor 264 and locks up. 204 is therefore released, and releases the register and lamps as before. Ringing current is sent from conductor G to battery on lower winding of relay 200, so that ring-back tone is sent by the repeating coil. When A<1> answers 209 energizes and locks up through 211 and back-bridge relay 200 energizes. Relay 201 then reverses the current over 130, 131, so that polarized relays 105, 100 operate to reverse current in the caller's line to operate a meter or the like. Release. When the subscribers hang up, relays 101, 102 release in turn, 103 being temporarily energized. Earth is removed from conductor 77 to release the automatic switches but is again put on when 103 releases to busy the repeater until the cord is fully released, relay 104 being held over 131. Release of 101 de-energizes 202, 203, so that 201, 207 are released at 224, and supervisory lamp SL lighted. On observing SL, the operator withdraws plugs P so that 250, 209, 211, 206 release, and relay 104 is released at 230. Premature removal of plug. Relays 211, 206 release, so that lamp CL is flashed from interrupter I. Operator can plug into a special jack for obtaining the called number from the caller. All registers busy. If switch C<1> has not found when the second digit has been registered on RG, relay 204 will not be energized and earth over conductor 263 will energize busy relay 210, which locks up to 224, sends back busy tone, and cuts the stepping circuit of C<1>. Busying a vacant B operator's position. By removing the plug P<1>, relay 248 is released to energize relay 249. Earth over conductors such as 253 energizes relays 104 of all the repeaters E connected to the position so that the test contacts 74 are earthed.