Outer conductor fault location in telecommunication cables - uses pulse interrogation technique and remote amplifier gain control

摘要

In order to locate cable faults, a sequence of pulses is induced in the live amplitudes of which at one end of the line give an indication of the amplifier nearest which any fault lies. This technique is already in use, though not to locate outer conductor faults, and two remote amplifier gain control circuits are described which allow the method to be extended to this case. The control circuit switches the gain control element of the remote amplifier (RST) to a fixed voltage when the supply current is reduced. This consists of two comparator linear amplifiers (IC1, IC2), the first with a hysteresis characteristic (Rb) and a number of voltage defining diode and resistance chains. These switch current to a heating element (R13) near a gain defining thermistor (RST) to give the control required. The second circuit, which is similar, switches the amplifier gain to a fixed level when the supply current is increased.