Patent GB-299007-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1928-07-10
Abstract: 299,007. Associated Telephone & Telegraph Co., (Assignees of Tharp, V. S., and Wicks, J.). Oct. 19, 1927, [Convention date]. Automatic and semi-automatic exchange systems. - In a system which includes private branch exchanges and in which a local connection may be broken down in favour of a toll call, certain connectors may be used either in local or toll connections to individual subscribers' lines, while special toll rotary connectors are employed in toll connections to P.B.X. lines. Toll call to individual subscriber over toll selectors TTS, TS and toll and local connector TLC. When the operator plugs in, line and release relays 24, 25 energize and connect up relay 13 (lower), and the vertical and rotary magnets of the selector TTS operate in the usual manner, and relay 14 being energized at the first vertical step. Switching relay 23 operates, and connects the line relay of the second selector TS in series with relay 13 (upper), impulses being repeated over this circuit by line relay 24. The selector TS is of the ordinary type except that the ring control wire 100 is extended to the fourth wiper 403 on the completion of its operation. In the connector TLC, line relay 311 energizes over relay 13 (upper), and the vertical and rotary ma.gnets operate in the usual manner, while reverting control relay 316 energizes over ring control wire 100 when change-over relay 314 pulls up, and locks. Ring cut-off relay 317 (upper) energizes and locks to ring control wire 100. Two-step relay 315 energizes fully when series relay 319 falls back after the rotary movement. Wanted line idle. Busy relay 318 is connected to test wiper 602 until series relay 319 falls back, but is inoperative if the line is idle. Relay 315 disconnects line relay 311 and switching relay 320 energizes, and test wiper 602 is connected to earth through resistance R' to mark the line busy in a toll call. Relay 13 falls back and connects up reversing relay 12 and feed relays 20, 21. Polarized relay 2 responds to the current reversal and lights lamp L. The operator throws key K to the ringing position, and relay 11 responds and connects up relay 22, which removes earth from wire 100 to release ring cut-off relay 317 to initiate ringing from the connector TLC. On the reply of the called party, relay 317 (lower) energizes again and locks, and relays 20, 21 energize, disconnecting line relay 24 from the loop, but maintaining it energized locally. Polarized relay 2 falls, back and extinguishes lamp L, which is subsequently relighted to give a clearing signal when the called party hangs up. Wanted line busy. Busy relay 318 energizes whether the line is busy in a local or a toll call and connects interrupter I over wire 308 to trunk wire 307. Series relay 319 on falling back locks busy Delay 318 and connects test wiper 602 and battery through resistance R to trunk wire 304. Release of relay 13 as before causes lamp L to light, while the intermittent energization of relay 20 over wire 307 causes it to flash. Relay 19 pulls up, substituting relay 15 for relay 22, and connecting relay 18 to trunk wire 304. If the line is busy in a toll call, relay 18 energizes over resistance R and connects up tone current T to signal the operator. If however, the line is busy in a local call, relay 18 is short-circuited by direct earth over test' wiper 602, and on hearing no tone, the operator throws key K to the ring- ing position to energize relays 11, 15. Direct earth is thereby disconnected from wire 100, and a short-circuit about the upper winding of busy relay 318 removed. This relay is differentially wound and relapses, disconnecting test wiper 602 from wire 304 and interrupter I from wire 307, and connecting up switching relay 320. Twostep relav 16 pulls up. The operator may now talk to the subscriber engaged in the local connection. On a second operation of key K, relays 11, 15 pull up, and earth is connected to both trunk wires. Assuming the wanted party to be the called party in the local connection, the lower windings of the relays like 310, 313 in the connector are short-circuited, and the latter being differential operates and connects up the release magnet like 323. The unwanted subscriber hangs up and effects the releases of the remaining switches. Two-step relay 17 energizes, and relays 16, 19. 14, 22 fall back. Feed relays 20, 21 are connected up, and the operator may, if necessary, ring the wanted party via relav 22. A local connection over a local connector which has the relays like 315, 316 omitted is released in a similar manner. Assuming now that the wanted party to be the calling party, earth on both trunk wires operates differential relay 121 at the first selector S<1> by short-circuiting one winding, and release magnet 122 restores the switch and initiates the release of the succeeding switches. The selector S<1> is otherwise similar to that described in Specification 285,365. Toll call to a P.B.X. over toll selectors TTS, TS and toll rotary connector TRC. In the connector TRC, line relay 411 connects up ring cutoff relav 412 (lower) which locks to ring control wire 100. Rotary series relay 415 on energization connects up relay 416, 417, and on relapse, closes a fresh circuit for relay 417. Assuming the first idle P.B.X. line to be 271-274, it is marked as shown at 6A, while the preceding lines are marked as shown at 6B or 6C. Stepping relay 420 energizes over test wiper 482 when relay 416 falls back, locks and connects up rotary magnet 422, and interaction takes place until the idle line is reached. Relay 417 then falls back and two-step relay 410 pulls up. disconnecting line relay 411, connecting up switching relay 419 and connecting earth through resistance R4 to test wiper 483 to mark the line busy in a toll call. Relay 419 connects direct earth to test wiper 482. The disconnection of line relay 411 releases relay 13 to light lamp L, and throwing of key K operates relay 11 to release ring cut-off relay 412, whereupon ringing current is connected up to operate a drop signal at the P.B.X. On reply, relay 412 re-energizes and lamp L is extinguished. All P.B.X. lines busy. Assuming the first line engaged in a local call to be 271-274, all the relays 494-496 are energized, and the first P.B.X. line is marked as shown at 6E. The line 271- 274 is marked as shown at 6B, and the intermediate lines as shown at 6C. When the connector engages the first P.B.X. line, and series relay 415 relapses, test relay 418 (lower) energizes over test wiper 483, locks and connects wiper 483 in place of wiper 482 to stepping relay 420, consequently the hunting movement of the connector continues until the line 271-274 is reached, the resistance R93 being large enough to prevent the energization of relay 420. Busy relay 414 now energizes over wiper 482 and disconnects switching relay 419, and when two-step relay 410 pulls up, interrupter I is connected to wire 405 to flash lamp L to give a busy signal. The operator may set up the desired connection in the same way as in the case of an individual subscriber engaged' in a local call by operating key K repeatedly, the first operation releasing busy relay 414 and energizing switching relay 419, the second releasing the local connection, and the third initiating ringing. The rotary connectors used for local calls are similar to that described in Specification 180,331 with the addition of a differential relay in series with the back-bridge relay which serves to connect up the release magnet and unlock the switching relay. If all the P.B.X. lines are engaged in toll calls, the connector stops on the terminals 491-493, which are connected up as shown. Busy relay 414 energizes, and after the first operation of key K, battery through resistance R96 is connected to wire 408 to energize relay 18 and give a tone signal. If there is only one idle line, and this is seized before the connector TRC reaches it, the connector moves on to the terminals 491-493. Busy relay 414 does not energize, since test relay 418 is not operated, and switching relay 419 energizes after two-step relay 410 pulls up, so that the tone signal is given in addition to the lamp flash signal. At her second attempt, the operator obtains connection over the first P.B.X. line engaged in a local call. Metering.-In the toll and local connector TLC, back-bridge relay 310 on energization opens the locking circuit of change-over relay 314 to send back a booster metering impulse.