Testing telephone lines to determine electrical characteristics - using LF test signal between two wires or between either wire and earth for fault detection and location

摘要

A two-wired telephone testing system uses a 1f. test signal which is a multiple of the power line frequency. This test signal is applied between the two-wires or between either wire at a point of potential reference (ground). A measure of the integrated value of the current between the connected points is then made for a period equal to one-half cycle of the applied signal with one polarity and one-half cycle with the polarity of the measured signal reversed. The integration periods are selected to be in phase with the applied signal for determining conductance and 90 deg. out of phase for determining susceptance. DC; measurement can also be made for the same time periods.