| 摘要 |
PURPOSE:To elevate the accuracy of detection, by placing plural negative poles around one positive pole at necessary intervals, electrifying them, generating a magnetic field which is almost circular centering around the positive pole, and getting rid of restrictions of a defect detecting direction. CONSTITUTION:When negative poles 2 are placed around a positive pole 1 at an equal distance and also at equal intervals, a circular magnetic field centering around the positive pole 1 is generated and a main defect detecting direction 3 becomes a radial direction of 360 deg. centering around the positive pole 1. In this case, the interval between the positive pole 1 and the negative pole 2 are kept away so as to exceed an effective defect detecting range, even between the poles which are the most approximate to each other. The positive pole 1 moves in order in the part occupying each apex of a triangle whose one side length is a distance which is below 1/2 of the diameter of the effective defect detecting range, and when electrification is executed 3 times in all, a defect 4 which is in the triangle receives 3 times a magnetic field whose directivity is different, influence to the accuracy of detection by the directivity of a defect is disregarded, and the accuracy of detection of a defect is elevated. |
