Fleit & Jacobson
Apparatus for detecting the center of a welded seam in accordance with fundamental harmonic component suppression
 An apparatus first magnitizes a base metal with an alternating flux to cross the welded seam of the base metal and the resulting leakage flux from the welded seam is detected by at least one flux search element to generate an AC signal. The fundamental harmonic component corresponding to the magnetizing signal used for the alternating magnetization is eliminated from the AC signal and the resulting signal voltage is sampled at a fixed period corresponding to the period of the magnetizing signal, thus detecting the center position of the welded seam from the result of the sampling. The apparatus comprises a magnetizing coil arranged adjacent to the base metal for the alternating magnetization thereof, at least one flux search element disposed adjacent to the base metal for leakage flux detecting purposes, means for eliminating from the detected AC output signal of the element the fundamental harmonic component corresponding to the magnetizing signal used for the alternating magnetization and a sampling circuit for sampling the output signal voltage of the eliminating means at a predetermined period, whereby the relative positional relation between the flux search element and the center of the welded seam is determined in accordance with the polarity and the amplitude value of the output voltage of the sampling circuit. 
Nippon Kokan Kabushiki Kaisha
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Seigo Hironobu Toshihiro
Ando Akuzawa Mori