| 摘要 |
<p>PURPOSE:To surely detect the damaged section of the coated film of an embedded conduit in a non-contact state by passing AC current to the embedded conduit, detecting the magnetic field component in the direction perpendicular to the pipe axis generated on the ground by means of plural magnetic field detectors and subjecting the same to a prescribed arithmetic processing. CONSTITUTION:The AC current I is supplied between the embedded conduit 1 and an embedded ground electrode 4 so that the magnetic field is generated on the ground surface 6. Perpendicular and horizontal magnetic field detectors 21, 22 are mounted on a carriage 7. The detection signal S1 of the detector 21 is subjected to the prescribed arithmetic processing by a computing element 26 via an amplifier 23, a BPF 24 and an AC/DC converter 25 and is then outputted to a recorder 27. The detection signal S2 of the detector 22 is outputted to the recorder 27 via an amplifier 28, a BPF 29 and an AC/DC converter 30. Further, the potential difference detection signal S3 between the front and rear wheels of the carrier 7 detected and amplified by a differential amplifier 32 is outputted to the recorder 27 via a filter 3 and an AC/DC converter 34. The outputs of magnetic field sensors 30a, 30b are computed by the computing element 26 and the change in the magnetic field by the damage of the coated film is detected in such a manner.</p> |
