| 摘要 |
PURPOSE:To suppress influence due to harmless outer diameter/thickness variation part by arranging detecting coils so as to be inclined from the axial core of a subject to be detected nonrectangularly. CONSTITUTION:In a head part 5, differentially coupled coils 52, 53 are wound around the external periphery of a bobbin 51 at two positions with inclination by a required angle theta from the position intersected with the axial line at right angles. Since both coils 52, 53 are opposed to the thickness variation part Pa only at a part of the periphery, the difference of output signals from both coils 52, 53 is not almost changed and influence due to the thickness variation part Pa is extremely reduced, so that error recognition with an output signal from a harmfull defect. |
