DETECTION OF ANTICORROSION COVER DAMAGE POSITION FOR BURIED METAL PIPES

摘要

PURPOSE:To detect a cover damage position accurately, by using a reference signal with the frequency the same as that of an AC signal for measurement when a ground surface potential difference is measured employing a wheel electrode. CONSTITUTION:A receiver 7 with a wheel electrode 8 is placed on the surface of ground where a metal pipe 2 provided with an anti-corrosion cover 1. An AC signal current runs is supplied by a measuring signal transmitter 6 between the metal pipe 2 and an opposed pole 5, and a potential difference is measured between two points on the ground surface with the wheel electrode 8 moving along the metal pipe 2 to be inputted into a detection signal input section of a lock-in amplifier 9. A signal with the frequency the same as that of an AC signal current is supplied from a reference signal oscillator 10 to a reference signal input section of the lock-in amplifier 9. After a noise signal with the frequency different from that of the reference signal is removed from a detection signal and changes in the phase are detected to learn the position of a cover damage part. This enables elimination of a wire for reference signal transmission thereby facilitating the detection of a damage position regardless of a longer distance between the transmitter 6 and the receiver 7.