DEVICE AT A TELEPHONE SUBSCRIBER TERMINAL FOR DISCONNECTING ONE OUT OF TWO ALTERNATELY AND AUTOMATICALLY CONNECTABLE SUBSTATIONS BY THE EXCHANGE IN CASE OF AN UNDESIRED LOOP CLOSURE IN ONE OF THESE SUBSTATIONS

摘要

1. A device in a telephone subscriber connection for switching off, by a signal from the telephone exchange, one of two alternatively automatically connectable user's stations (Sp1, Sp2) when an inadvertent loop-closure occurs at this user's station ; with a switch-over device (W) interposed between the telephone line and the user's stations which, when the loop is closed in one of the two user's stations, connects this one to the telephone line and disconnects the other one ; and with a testing device (P) for testing, from the telephone exchange, the telephone line between the telephone exchange and the subscriber connection ; there being connected to the telephone line, just before the subscriber connection, a switch-over device (U) which is activated by a control signal from the telephone exchange for disconnecting the subscriber connection from the telephone line and connecting the testing device instead ; the testing device containing a source for producing supply voltages ; the testing device delivering test signals at a specified frequency to the telephone line and then, after completion of the test cycle, a re-set signal to the switch-over device for re-connecting the subscriber connection to the telephone line ; characterised in that between the switch-over device (W) and each user's station (Sp1, Sp2) there is interposed a disconnected-device (15, 25) for disconnecting this user's station (Sp1, Sp2) from he switch-over device ; each disconnect-device (15, 25) having, interposed in the conductor between the user's station (Sp1, Sp2) and the switch-over device (W), a bistable switch (K11-K12, k1, K21-K22-k2) with a set terminal (Se1, Se2) and a re-set terminal (RS1, RS2) ; the set terminal (Se1, Se2) being connected, in each case, over the switch-over device (W) to the telephone line (a1, b1), the re-set terminal (RS1, RS2) being connected to a short-circuit monitor (16, 26) connected to the input terminal of the user's station ; each short-circuit monitor (16, 26) delivering a re-set signal as soon as the loop in its user's station (Sp1, Sp2) is interrupted after separation from the switch-over device (W) ; and in that the source (7) for delivering supply-voltages to the testing device (P) is connected to a lead (b1) of the telephone line (a1, b1) connected to the switch-over device (W), for delivering a set signal.