Circuit arrangement for determining the zone of origin of a telephone connection

In a telecommunications system of the type in which a plurality of repeaters are permanently assigned to respective zones of origin and operate to seize a register by way of respective switches of a coupling device and a selection switching device which selects a free register, and in which a control path extends from each switch through the selection switching device and through the register, the seized register causing the emission of a switch-through command, the improvement in combination therewith comprising:

• test signal producing means connected to the control path and connected to receive and operate in response to the switch-through command to apply a test signal to the control path;
• a plurality of opto-electronic switching elements each connected to a respective switch on the repeater side thereof and operated to indicate the zone of origin assigned to the respective repeater in response to a test signal and to produce a corresponding electrical signal;
• a plurality of delay circuits each connected to a respective opto-electronic switching element for delaying the respective electrical signal by a respective predetermined time which is matched to the duration of expected interference pulses;
• a plurality of trigger circuits each connected to a respective delay circuit and operated by a respective delayed electrical pulse to produce an output signal;
• first gating means connected between said plurality of trigger circuits and said test signal producing means for gating through an output signal to terminate the test signal;
• said test signal producing means including timing means for causing transmission of the test signal for an interval which exceeds the maximum predetermined delay time;
• second gating means connected to said plurality of trigger circuits and operated in response to multiple output signals to produce a further output signal;
• and
• recording means connected to said second gating means for recording the further output signal.