| 摘要 |
A flaw detection apparatus for detecting flaws at the outer surface of a product, such as a steel bar, wire or steel pipe, which is round in section and produced by the hot rolling, by use of a probe of non-contact type and rotating around the product to be inspected, the apparatus providing a means for suppressing vibrations of an object to be inspected, a means for measuring a distance (lift-off) between the object to be inspected and the probe, and a means for carrying out positional control on the basis of the detection result of the lift-off measurement so that the axis of rotation of probe is allowed to be coincident with the axis of object to be inspected. In a case of using the eddy current inspection for the flaw detection, two coils of standard comparison system are used and a mixed signal of a plurality of frequencies is applied to the coils so that a signal obtained by the probe coils suppresses the signal component caused by the lift-off variation and corrects the flaw signal caused by existence of the signal component, thereby eliminating the influence of lift-off variation and enabling measurement with high accuracy. |
