Improvements in or relating to Telephone Exchange Circuits

1,191,200. Automatic exchange systems. STANDARD TELEPHONES & CABLES Ltd. 1 Aug., 1968, No. 36736/68. Heading H4K. A telephone exchange which may be of the type described in Specification 1,101,567, employs a bidirectional translator incorporating a distribution frame the wiring of which determines directory number to equipment number and vice versa translations. The marker can thus on receipt of a directory or equipment number rapidly obtain the other number. The directory number may be needed for metering purposes. In the cross-bar exchange described the translator employs a number distribution frame with terminals on one side characterizing equipment numbers selectively jumpered to terminals on the other side and characterizing directory numbers. An excess of directory number terminals provide freedom for reallocation. For a P.B.X. a plurality of equipment number terminals are strapped to a single directory number terminal. Coupled to the terminals are relays arranged to code the corresponding numbers. On the equipment number side the relays are arranged in sequentially operative groups of 5, 5, 3 and 11 relays respectively. One relay in each group operates. The first two groups have lockout networks which ensure that in the event of two simultaneous calls only one relay in each group receives holding potential. The first two groups identify the rack and the crossbar switch number within a rack respectively while the other two groups identify a single line or trunk connected to that crossbar switch. On the directory number side, groups of 200 terminals are connected to separate sub-units. Each sub-unit has two " hundreds " relays and twenty " tens " relays (ten for each " hundreds " relay). These relays are further connected to three further groups of five relays. The further groups of relays each register a digit of the directory number in " 2 out of 5 " code. The manner in which individual relays within their groups are selected for operation is not given. A relay, whose circuit is not detailed, fails to operate unless the further groups register a directory number in proper " 2 out of 5 " form. In an alternative arrangement and particularly if sealed contact reed relays are to be used in the speech path electronic equipment instead of relays could be used in the translator.