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

An apparatus for detecting the center of a welded seam of an AC magnetized welded steel material by detecting leakage flux from said welded seam comprising:

• an AC power source having an output,
• magnetizing means connected to said AC power source for AC magnetizing said steel material by magnetic flux crossing said welded seam,
• leakage flux search means fixedly mounted integral with said magnetizing means for detecting leakage flux from said welded seam so as to provide an induced voltage corresponding to a change in said leakage flux, said induced voltage comprising a fundamental harmonic corresponding to an excitation voltage waveform used for said AC magnetization and a pulse like component corresponding to said welded seam, and
• detecting means responsive to said induced voltage from said leakage flux search means for detecting a center position of said welded seam in terms of a relative positional relation between said center position and said leakage flux search means;
• wherein said detecting means comprises first means for eliminating from said induced voltage the fundamental harmonic component corresponding to the excitation voltage waveform used for said AC magnetization while leaving at least the pulse-like component, second means for producing from said output of said AC power source a gate pulse signal having a predetermined period for sampling, and third means responsive to said gate signal for sampling at said predetermined period, said induced voltage having said fundamental harmonic component eliminated therefrom and having at least said pulse-like component, whereby in accordance with the polarity and voltage value of a sampled output from said third means the center position of said welded seam is detected in terms of a relative positional relation between said center position and said search means.