GB551697A - Improvements in or relating to telephone systems - Google Patents

Abstract

551,697. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd., COMYN, F. E., and FRYDMAN, E. Sept. 2, 1941, No. 11193. [Class 40 (iv)] In a small private automatic exchange of the kind described in Specifications 389,867 and 529,169, the line relays R of privileged subscribers are connected in series with a common differential relay EF, which when operated by the actuation of an earthing key at the substation causes the connection of the line to an outgoing junction. Finderconnector links LFS, CS are provided for setting up local calls, while the junctions terminate in finders EFS. The operation of relay EF connects up relay SA which opens the start circuit for the finders LFS and disconnects the line relays of other subscribers, that of the calling subscriber being transferred by a slow-operating relay SC through relay SE which pulls up when the key is released and makes a start circuit for an allotted finder EFS. Relays SE, SA, SC are released by the operation of cut-off relay K. If a local link has already been taken in use when 'the earthing key is actuated, a differential relay OG brings about the release of the link and of cut-off relay K. By actuating his key again, the privileged subscriber may operate a differential relay TC in order to hold the junction while setting up a local call over leads 13, 14 in the manner described in Specification 389,867. On an incoming call, circuit changes occur which cause the finder EFS to hunt for an answering subscriber's line when he removes his receiver. Such subscribers are provided with an earthing key to enable them to transfer calls if necessary, as mentioned above, but they can only make outgoing calls if their lines are connected to the common relay EF. When all junctions are busy, relay SC applies busy tone from lead 12.