| 摘要 |
PROBLEM TO BE SOLVED: To provide a device for detecting a magnetic flux resulted from a minute defect present in a material to be inspected or a minute iron powder or the like included in the material to be inspected with high sensitivity and high S/N. SOLUTION: A magnet 2 for magnetizing the material to be inspected 1 is provided in the vicinity of the material 1 traveling an arrowed direction, and the magnetic flux from its magnetic poles N and S magnetize the material 1 to a value close to a saturated magnetic flux density. Three magnetic sensors S1, S2 and S3 are provided at equal intervals in the middle of the magnetic poles N and S. In (B), three probe coils are used as the magnetic sensors and connected so that S1 and S3 at both ends of the three probe coils are in the same phase and the central S2 in the reverse phase, and the connecting wire is connected to a preamplifier 3. S1 and S3 have the same number of turns, and the number of turns of S2 is set to two times this number of turns. The voltage corresponding to the difference between the sum of leakage the magnetic fluxes detected by the magnetic sensors S1 and S3 and two times the magnetic flux detected by the magnetic sensor S2 is inputted to the preamplifier 3 and amplified.
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