| 摘要 |
PURPOSE:To detect a defect preventing mutual interference among a plurality of probe coils, by feeding a high frequency voltage to the probe coils at each time division while defect signals of the probe coils are detected at each time division. CONSTITUTION:A flaw detection of a tubular bar material is performed with a plurality of probe coils 1 (1a-1x). Here, a high frequency voltage from a high frequency oscillator 11 is applied sequentially to the probe coils 1 with a time division circuit 12 through a bridge circuit 2 at each time division. Then, the probe coils 1 form magnetic fields separately at each time division and an eddy current is generated in the tubular bar material with the action of electromagnetic induction by the magnetic fields and when any defect exists, the value of the eddy current changes. The current values are sent to a phase detection circuits 4 and 5 to detect a defect with a flaw judging section 9. Since a high frequency voltage is applied to the probe coils at each time division, this eliminates interaction due to electromagnetic induction among the probe coils, thereby enabling correct and accurate detection of defects.
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