Abstract: Open circuit faults in a cable are located by applying a step function DC voltage to one end of a conductor along the cable, for example the metallic shield along a fibre optic cable. The DC current along the conductor is measured over a sampling period and integrated to determine the capacitive charge on the cable. The distance between the end of the conductor and the open circuit fault is computed from the calculated charge and the known capacitance per unit length of the conductor. The DC current in the conductor is measured by sampling the current at a predetermined sampling frequency. The sampling frequency is preferably an integral multiple of the local AC mains power frequency, either 60 Hz or 50 Hz to eliminate the effect of induced AC voltages in the calculations.

Abstract: The invention provides an interactive means to locate and identify underground utilities. The apparatus is used with a marker associated with an elongate electrical conductor, which may be a cable shield or a trace wire. It includes a remote, portable probe that is used to transmit a RF signal to be received by a transponder associated with the marker. The transponder is powered by a DC potential on the conductor. In preferred embodiments it has the capability of communicating with a terminal unit over the conductor to transmit information and instructions between the probe and the terminal unit.

Abstract: A transmission enhancement system is used for strengthening low frequency cable locating signals on the metallic shields of long underground cables. The system includes equalization circuits on the cable armour or shield at regular intervals, for example at splice locations. The equalization circuit includes an inductor that significantly reduces the rate of attenuation of the low frequency tone signal and greatly enhances the strength of the signal at distances where the signal would otherwise be very weak or unusable. The equalization circuit may be a resonant circuit having a capacitor connected in parallel with the inductor. The capacitor compensates for the inductor's attenuation of high frequency tones for local location purposes. The preferred embodiments of the equalization circuit include a surge arrestor coupled in parallel with the inductor and capacitor.

Abstract: A method and apparatus are used for locating cable breaks and resistive faults in cables, including fibre optic cables. The conductive shield or armour of the cable is divided into sections, usually at a splice. A step function voltage is applied to one end of the conductive shield. Remote sensors at the end of each section monitor the voltage and current as a function of time and at steady state. The measured data are encoded as current pulses and transmitted along the armour to the end of the cable. A computer at the cable end calculates from the measured voltages and currents the capacitance of each section of the shield. A broken section is identified by comparing the calculated and original capacitances of the sections and the distance along the broken section to the break is calculated from the calculated and original capacitances of the broken section.