| 摘要 |
PURPOSE:To detect easily and properly a coated and damaged position by transmitting a detecting signal detected out of two wheel electrodes in a receiver and a reference signal from a transmitter to a phase detector. CONSTITUTION:With the use of the transmitter 6, when an AC signal voltage is impressed on a metallic tube 2 and a counter electrode 5 to flow an AC signal current between a coated and damaged part 3 and the electrode 5, the current generates a potential distribution 27 in the ground with the damaged part 3 as a center. After water is sprayed on the ground surface right above the metallic tube 2, the receiver 7 is traveled on the surface right above the metallic tube 2, and two wheel electrodes 8 detect a potential difference between two points on the surface. On the other hand, the reference signal synchronizing with an AC signal voltage is inputted to a waveform shaping device 25 in the receiver 7 from the transmitter 6 through an electric wire 26, converted into a rectangular wave and inputted to a phase detector 9. Then signals converted into DC and AC are transmitted to a low-pass filter 10, and only the DC component of the signals is extracted by removing the AC component from said signal. Then the signal is DC-amplified 24 and displayed 11. |
