Patent GB-325026-A (GB)
Title: Improvements relating to automatic telephone systems
IPC: H04Q3/00
Filed: 1928-11-19
Abstract: 325,026. Siemens Bros. & Co., Ltd., and Christian, D. A. Nov. 19, 1928. Automatic and s e m iautomatic exchange systems. -In final selectors used for both ordinary and preferred calls, a relay which is connected to one of the speaking conductors when a wanted line is found busy operates in response to a directcurrent signal sent forward from a toll-operator's position to close a speaking circuit between the operator and the wanted subscriber and to prepare a test circuit by means of which the wanted line is seized as soon as it becomes free provided that the operator's signal has ceased. If the existing connection is one involving a manual operator, release by the latter may be expedited by the transmission of a flashing signal from the toll-operator's position. In the system shown, toll calls are established from a toll-operator's position, Fig. 1, over a special group selector, Fig. 2, and a final selector, Fig. 3, which is also used for ordinary calls. The group selector has means for repeating forward the toll-offering signal which is transmitted from the toll position by means of key TO and if the connection involves intermediate exchanges the signal will be repeated at each exchange by a similar group selector. Toll call; group selector. When the cord, Fig. 1, is inserted, relays AA, V, DD, operate and when the dialling key SD is thrown and the dial DS pulled off-normal, relay DR is operated and locks over the a-wire in series with relay TTL which energizes relay TM. Impulses are repeated to the vertical magnet VM and at the end of the digit the relapse of relay DD completes an interrupter circuit for the rotary magnet RM, relay L having operated at the end of the first impulse. When an idle final selector is found, test relay TT switches through. Final selector. Impulses repeated by relay AA over the b-lead to relay A are steered in known manner to the vertical and rotary magnets VM, RM and at the end of the units digit between the relapse of relays D, G, test relay T is connected to the test wiper. If the wanted line is free relay T pulls up and cuts off relay A so that relay TR(ii) is short-circuited and on the relapse of relay G, ringing relay S operates. When the called subscriber replies, relay TR(i) operates and locks up over winding (ii), short-circuiting relay S. Relay Y, Fig. 2, operating over the called loop transmits an answering signal to the toll-operator, who by the restoration of key SD at the end of dialling has released relays TTL, TM and operated relay Q. Wanted line busy. On the relapse of relay G, relay TR(ii) operates (relay S being shortcircuited) and connects up the busy lead to which busy tone and battery are intermittently connected by relay LF under the control of cam BF. On receiving this busy signal, the operator presses key TO which applies battery to the awire energizing relay TTL which repeats the signal by connecting battery over relay R to the outgoing a-wire. At the next release of relay LF relay TL operates, completing a talking connection to the wanted subscriber and preparing through an auxiliary relay TLL anew circuit for the test relay T. Having requested the wanted subscriber to hang up, the toll-operator restores key TO so that relay TL releases and the new testing circuit for relay T is completed. When the wanted line becomes free relay T operates and releases relay TR which in turn releases relay TLL so that relay S operates and rings the wanted subscriber. The toll-operator may rering the subscriber by again pressing key TO when relay TTL operates and releases relay Q so that relay SS operates and supplies ringing- current from the group selector. The final selector may be modified, so that automatic ring- ing of a subscriber who has released himself from a local connection is prevented, by connecting relay S directly to battery and by including a back contact of relay T in the circuit of relay TLL(ii). In this case the subscriber will be rung when the toll call matures by ring- ing-current supplied from the group selector under the control of the operator in the manner already described. Signalling to a manual operator who may be holding a local connection. If, after requesting the wanted subscriber to hang up, the tolloperator does not get the clearing signal, she assumes that the call is held at an operator's position and operates the key FK. Relays AA, A are de-energized and relays TTL, TL operated so that a bridge is closed across the outgoing conductors at the final selector. Repeated opening and closing of this bridge by means of key FK causes the manual operator's lamp to flash.