Patent GB-583373-A (GB)
Title: Improvements in automatic switches for use in telephone or like systems
IPC: H04Q3/00
Filed: 1944-06-15
Abstract: 583,373. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd., TAYLOR, R., and BAKER, G. T. June 15, 1944, No. 11440. [Class 40 (iv)] A final selector, which provides ordinary facilities when seized by a subscriber, can also be used by an operator as a trunk-offering connector, in which case different busy signals are given according to whether the wanted subscriber is engaged on a local or a longdistance connection. The " rectangular release " type of switch shown in Figs. 1 ... 3, which is operated in known manner when seized by a subscriber, has two sets of wipers, the second set being switched in by a relay WS operated at the end of the vertical train when the switch is seized over conductors 2+2 from an alternative level. Seizure by an operator over - 1TK, + 1TK causes relay OP to operate and lock at the end of the rotary digit. OP operates F to ensure ringing does not start automatically. If the called subscriber is idle, H and J operate followed by relay BD which applies busy tone from wire 12 to the private. The operator then throws her ringing key, earthing the line to operate the differential relay DF which short-circuits relay F to transmit ringing current, after which the connection is completed as usual. If the wanted line is busy, G and not H operates as usual and operator receives busy flash from wire 10. If the subscriber is busy in a local connection, no tone is received either from leads 12 (BD not operated) or 18 (OP operated). If the subscriber is busy in a long-distance connection, tone applied to the private as above reaches relay A via condenser QD and OP6. In the former case, to cut in the operator throws her ring key, energizing DF which operates relay CN so switching the speaking conductors through. G holds in series with CN until DF is released. To break down the connection, the operator again throws her ring key and DF operates BD which connects earth to the private through the low resistance coil of the retard TB. If the wanted party is the calling party, this shunts down the cut-off relay in his line circuit which may be that disclosed in Specification 574,312, and if he is the called party it shunts down relay H in the final selector. Relay WS acts as before to switch to the second set if the operator seizes the switch over conductors - 2TK, + 2TK. The switch as shown can be used to hunt over a P.B.X. group of 2 to 10 lines. Wiper P2 picks up battery on the first line and earth on the last line, while intermediate lines and ordinary subscribers are unwired. On release of C at the end of the rotary digit battery picked up by P2 operates HS to the release alarm earth 16. On busy lines, H is shortcircuited and G operates in series with the lower coil of HS as also does RM, stepping taking place as a result of interaction between RM and G. On reaching an idle line, G holds up in series with H which locks over its right-hand coil and short-circuits G which then releases, but not until H has disconnected RM and HS. HS holds A while G operates. If all lines are busy, earth on P2 maintains G. HS releases, leaving G locked up to put out busy signal.