Apparatus and method for detecting the location of metallic objects having alternating current passing therethrough

摘要

A method of detection of inaccessible metallic objects such as gas, electricity, water or telecommunications systems (lines) through which an alternating current is flowing, comprises making at least three spatially separated measurements of the magnetic field associated with the current. Signals derived from the measurements are compared in a detector which gives an output indication when the signals derived from the measurements at the two outer locations are equal and each less than the signal derived from the measurement at the intermediate location. A suitable sensing device has four equally spaced pickup coils and operates at a frequency of 43KHz. The alternating current detected in the metallic objects may be induced by a separate transmitter.