Apparatus for detecting the center of a welded seam in accordance with fundamental harmonic component suppression

DETAILED DESCRIPTION It is a principal object of the invention to provide an apparatus which is capable of detecting with a high degree of accuracy the center of the welded seam of even such a base metal in which the difference in magnetic properties between the base metal portion and the welded joint is very small.
It is another object of the invention to provide such apparatus in which a base metal is magnetized with an alternating flux from a coil energized by commercial power supply and the resulting AC leakage flux from its welded seam is detected to thereby detect the center of the welded seam in a noncontact manner.
It is still another object of the invention to provide such apparatus in which variations in the center position of the welded seam of a base metal can be detected continuously along the lengthwise direction of the seam in terms of the relative positional relation between the center position and the leakage flux search means.
In accordance with the invention there is thus provided an apparatus for detecting the center of a welded seam comprising a pair of magnetizers which are preferably arranged on both sides of and adjacent to the welded seam of a steel material so as to apply an AC magnetic flux to the steel material to cross the welded seam, a leakage flux search element arranged between the pair of magnetizers and fixedly attached to associated the magnetizers in the vicinity of the welded seam so as to detect the leakage flux from the welded seam of the steel material AC magnetized by the magnetizers, and a detecting circuit whereby the fundamental harmonic component corresponding to the exciting voltage waveform used for the alternating magnetization is eliminated from the AC voltage induced in the leakage flux search element and the resulting signal voltage is sampled at a predetermined period, whereby the center position of the welded seam is detected in terms of the relative positional relation between it and the leakage flux search element in accordance with the polarity and voltage value of the sampled output generated from the detecting circuit