GB191417446A - Improvements in Telephone Systems. - Google Patents

Abstract

17,446. Conner, M. S., and Robinson, R. E. July 23. Exchange systems.-Relates to a privatebranch exchange system of the kind in which local connexions are supplied with speaking- current by a battery B at the branch-exchange, while, in the case of a connexion between a main - exchange line and a local line, the battery B is cut out by a relay R1 in the sleeve circuit, which switches the connexion metallically through. In the case of a local connexion, the subscribers are supplied independently with current through the supervisory signals SS1, SS2 and inductances I1, I2, while in the case of a main line connexion, the supervisory signals SS1, SS2 are switched in series across the condenser C2. The cord circuit is symmetrical, so that either plug can be used for answering a main line call. The depression of the listening-key K bridges a relay R2 across the cord circuit to give a signal at the main-exchange. The relay R2 locks itself independently of the key K, but is cut out of circuit by the supervisory signal SS2 when the local subscriber answers the call. When the local subscriber hangs up his receiver, the signals SS1, SS2 are de-energized, a bell D is rung, and a clearing signal is simultaneously given at the mainexchange. Specifications 23,812/12 and 9818/13 are referred to.