| 摘要 |
PURPOSE:To obtain a magnetism probing method having high sensitivity by adding and averaging the output voltage of each magnetic sensor placed annularly in a pipeline, and comparing the difference of said voltage and an output voltage obtained by each sensor by a differential amplifier, at the time of probing a pitting corrosion generated after having laid the pipeline. CONSTITUTION:Plural magnetic sensors 31-3n in a pipeline 1 are placed annular ly in one cross section, a leakage flux phi generated from a pitting corrosion H is detected, and an obtained output voltage is inputted to a multiplexer 5 and an adder 9. Subsequently, from the multiplexer 5, the output voltages of the sensors 31-3n brought to a time division by a gate signal oscillator 7 are outputted, amplified by a signal amplifier 6 and inputted to a differential ampli fier 10. In this state, an output voltage in which the influence of the pitting corrosion H appears and an output voltage in which an influence by welding of the periphery of a pipe are generated, and in the differential amplifier 10, a reference voltage determined in advance and a variation by the pitting corro sion H eliminating the influence of welding are compared, and the size of the pitting corrosion H and the position on the periphery are recognized.
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