Norscan Instruments Ltd.

Norscan, Inc.

Myron Loewen

David E Vokey

Kenneth N Sontag

A constant current termination is provided for cable locating tones on communication and control cables that may be buried or placed in underground duct structures. The constant current termination limits the current on each branch of the cable to that required for cable location, thus ensuring that branches furthest from the tone source have adequate current for location purposes. The termination is the same for each branch, regardless of its position along the cable system. This eliminates the need to calibrate and recalibrate termination distances for a cable on installation and when branches are added. It also allows the location of damaged cables where the tone signal strength on a damaged branch is less than that for which the termination was designed.

Locating system for a cable system having a backbone and branch cables defining multiple terminations

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. Resistive faults in the cable are located by calculating a fault resistance of each section of the shield from the measured steady state voltages and currents. A section containing a resistive fault is identified from the magnitude of the calculated fault resistance and the distance to the resistive fault is calculated from the measured steady state voltages and currents of the faulted section.

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Myron Loewen