GB712027A - Circuit arrangements for automatic telephone systems, particularly pabx-installations - Google Patents

Abstract

712,027. 'Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd. Oct. 24, 1952 [Oct. 30,1951], No. 26734/52 Class 40 (4) In a PABX having outgoing junctions over which calls may be established in a number of directions, the setting up of a call in one of these directions operates a first relay (H) and the termination of the call operates a second relay (e.g. C), which indicates to an operator the direction in which the call was set up, and the first relay places the release of the calling line and said first and second relays under the control of the operator. The subscriber is connected to the outgoing repeater over finder AW, relay P operating and short circuiting its high resistances winding to mark the subscriber busy. Relay I repeats the dialled impulses over the exchange line and also to the drive magnet of the switch D, with hold relay V and dialling relay X operating in the usual manner the former bringing up S. If the call is a local one (low-fee) the first digit to be dialled will be between 1 and 9 and relay S which holds until the end of the digit then releases. When the calling subscriber hangs up the switch D is homed and the repeater released in the normal manner. If a toll or trunk call is made however the digit O is dialled and S remains held over the tenth contact of wiper D1 When the next digit is dialled the switch is stepped to a contact such as 03 whereupon H comes up during the release period of S release and makes the release of the calling subscriber dependant on key Tr. When the calling subscriber hangs up relay C operates over wiper D2 indicating the class of call and lighting a corresponding lamp and operating common visual and audible warning signals KL, KW. The operator may now depress the key FsT to light a lamp TL identifying the calling subscriber. The subscriber and the repeater may now be released by the operation of key Tr which releases H.