PURPOSE: To enable an encounter test without ringing telephone terminal equipment by instantaneously detecting a voltage change caused by incoming of a calling signal sent from a station exchange and short-circuiting a line. ;CONSTITUTION: When the unused state of the line is confirmed, an incoming call signal detecting part (incoming call signal detecting circuit 3, waveform shaping circuit 4 and flip-flop 5) is connected through an automatic closing/ opening circuit 1 by a changeover switch S and a calling signal (AC75V) is transmitted from the station exchange by dialing a telephone number to be confirmed from the other line. The incoming call signal detecting part (incoming call signal detecting circuit 3, waveform shaping circuit 4 and flip-flop 5) detects the rising of this calling signal and controls a relay driving circuit 7 by a relay lamp control part 6, and a relay K of the automatic closing/opening circuit 1 is switched from the opened side to the short-circuited side within about 30msec after the incoming of the calling signal. At the same time, a lamp driving circuit 8 is controlled by the relay lamp control part 6 and a hold lamp R is driven.;COPYRIGHT: (C)1996,JPO
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