| 摘要 |
<p>A steel sheet flaw detector which comprises a magnetic measuring apparatus (5) which includes a magnetic sensor (11) disposed in the proximity of a moving steel sheet (1), detects the voltage waveforms on the positive and negative voltage sides of the voltage outputted from both ends of a coil when an A.C. power having a predetermined frequency and a predetermined voltage is applied thereto, and detects the magnetic intensity by comparing the waveform on the positive voltage side with the waveform on the negative voltage side; a first comparison circuit (7) which compares the magnetic detection signal (S) outputted from the magnetic measuring apparatus (5) with a first threshold value (TH1), judges a first magnetic detection signal (S1) exceeding the first threshold value (TH1) and a second magnetic detection signal (S2) not reaching the first threshold value (TH1), and detects a main flaw or flaws of the steel sheet (1); a peak value detection circuit (17) which detects a peak value of the second magnetic detection signal (S2) when the steel sheet (1) moves in a predetermined distance; a typical value selection circuit (18) which selects a predetermined value from a plurality of peak values (pi) detected by the peak value detection circuit (17); a second threshold value calculation circuit (8) which calculates a mean value of the typical values (Pa) and determines a second threshold value (TH2) corresponding to this mean value; and a second comparison circuit (9) which compares the second threshold value (TH2) obtained by the second threshold value calculation circuit (8) with the second magnetic detection signal (S2), and detects very small flaws of the steel sheet (1).</p> |
