Patent GB-298164-A (GB)
Title: Improvements in telephone systems
IPC: H04M3/64
Filed: 1928-10-04
Abstract: 298,164. Standard Telephones & Cables, Ltd., (Assignees of Caverly, H. C.). Oct. 4, 1927, [Convention date]. Semi-automatic exchange systems.-In systems in which calls from an automatic to a distant manual exchange are set up via a tandem office and in which the complete designation of the wanted line is registered at the first exchange, the exchange code only is transmitted at first to the tandem office and when the connection has been extended to the wanted exchange the numerical digits are transmitted straight through the tandem exchange to the distant operator. The retransmission of the exchange and numerical digits to the tandem and terminal operators, respectively, may be verbal by means of a " callannouncer " mechanism comprising a series of rotating drums each carrying a photographic record of the sound of one of the digits, the particular reproducing circuits required being successively selected in accordance with the setting off the digit-registering switches. Setting of registers; extension of call to tandem office. The eight dialled digits (three exchange-code, four numerical and one station) are repeated by relay 1100, Fig. 1, over relay 1190 and wiper 1108 to the magnets 1113 - - 1215, Fig. 3, of the digit registers. A district selector 259, 258 and a two-wire office selector 501, 502 are then set in accordance with a translated routing-number to extend the call to a tandem office, Fig. 2, and a circuit to test the condition of the inter-office junction is completed from relay 503 over brushes 501, 259, cams 220, 744, coil 402, cam 401 of the class register 400, Fig. 4 (which is set to position 3 for tandem calls), polarized relay 823, cam 774, high-resistance relay 839, cams 403, 824, 219, brushes 258, 502 to relay 503. Relay 839 operates in this circuit and causes the sender sequence switch of the register-controller to move to its 16th position in which relay 839 is shunted by a circuit from cam 774 over parallel back contacts of relays 411, 416 and cam 403. Relay 503 now operates, causing a finder-switch 500 to hunt for the calling trunk and when this is found relay 508 operates, energizing relay 505 which locks over its outer windings and resistances 510, 511 to the junction loop. This operation reverses the current in the loop so that relay 823 energizes. Transmission of exchange-code to tandem operator. Relay 823 completes a circuit for relay 405 which however has a shunting non-inductive winding connected up whenever relay 406 is operated to prevent the transmission of a mutilated digit. Relay 406 is operated over commutators 301, 302 at the times when the record drums are in operative position. The callannouncer comprises fourteen rotating drums 300 having alternate opaque and transparent sections, the latter bearing photographic records of the sounds of the ten numerial digits and the four station digits, respectively. The records are converted into electrical vibrations by photoelectric cells 305. At its first operation, relay 405 completes a circuit from lead 303 over the right hand windings of repeating coil 402, cam 421, and wiper 1171, so that the sound corresponding to the digit determined by the setting of wiper 1171 is repeated over transformer 306, amplifier A, and coils 402, 506, to the tandem operator. During the transmission, relay 406 operates relay 410 which at the end of the digit locks in series with relay 411 to cam 427 so that wipers 1173, 1175 are successively connected up for the transmission of the other exchange digits. After the third digit, relays 415, 416 operate and open the loop causing the release of relays 823, 505. Relay 416 also closes a circuit for moving sequence switch 420 into its 3rd position in which the operated counting relays are released. Completion of call. The insertion of plug 514 into jack 515 at the tandem, position causes relay 516 to operate over the tip and ring conductors in series with polarized relay 521, thus lighting call lamp 523. The throwing of the terminal operator's speaking key 525 energizes relay 518 which locks over the incoming loop and reverses the direction of current to operate relay 521. The latter energizes relay 505 so that polarized relay 823 operates as before to start the transmission of the numerical digits. Relay 521 also energizes slow-acting relay 520 which in turn operates relay 522. Relay 522 short-circuits resistances 510, 511 causing relay 528 in the office selector which is both marginal and polarized to operate. Counting relays 410 - - 415 operate as before to associate repeating coil 402 with wipers 1168 - - 1227 over cams 421 - - 423, respectively, but since relays 410, 411 are on this occasion locked over a back contact of relay 414 and cams 426, 427, the operation of 414 releases 410, 411. Relays 416, 417 operate for the fourth digit and 410, 411 operate again for the station digit. At the end of the latter, relays 411, 416 complete a circuit for relay 750 which opens the loop and initiates the release of the register-controller. At the office selector, the release of relay 528 moves the associated sequence switch to talking position. At the tandem exchange, relays 505, 520, 521 release, and at the terminal exchange relay 518 releases. When the called subscriber replies, relays 533, 517 operate reversing the battery connections to relay 516 so that relay 521 operates again, energizing reversing relay 504 to give answering supervision.