Method and apparatus to detect randomly distributed discontinuities in different directions in a longitudinally moving web using rotating probes in overlapped paths

摘要

The invention relates to a method and a device for detecting discontinuities in materials by means of probes sensitive to said discontinuities. According to the invention the material (1) is scanned preferably in the form of a web, by at least two probes (2, 6) which during the scanning sequence are moved above the material (1) in circular paths (3) and (7) in a geometrical plane which is essentially parallel to the geometrical plane of the material web. The circular paths have essentially equal radii and at least one first circular path (3) is arranged in front of a second circular path (7) and is displaced sideways in relation to the second path in such a way that essentially every surface element of the material web is successively covered by at least two circular paths (3) and (7) with such an overlapping that every half- circle segment is sideways overlapped by a consecutive half-circle segment, all seen in the travel direction of the material web.P PThe invention also relates to a device to carry out the above- mentioned method.