| 摘要 |
PURPOSE:To hold the detection precision constant approximately to improve the stability of defect check processing, by adding a correcting circuit, which corrects a discrimination level in accordance with the running speed of an object to be detected, to a discrimination level setting circuit for detecting a defect. CONSTITUTION:A video signal VS and an output signal (b) of a D/A converter 13 are inputted to a comparator 14, and the output signal (b) is made approximately equal to an envelope signal of the video signal VS. The output signal (b) of the D/A converter 13 is corrected in accordance with the running speed of the object to be detected by a discrimination level correcting circuit 19. A speed operating circuit 21 calculates the running speed of the object to be detected on a basis of the output of a speed detecting circuit 22 and inputs it to a CPU22. The CPU22 reads the amplification coefficient of a discrimination level corresponding to speed data from a memory 23 and sets this amplification coefficient to a D/A converter 24. The D/A converter 24 increases or reduces the level of the output signal (b) of the D/A converter 13 in accordance with the amplification coefficient to set a discrimination level SH, which corresponds to the running speed of the object to be detected, to a comparator 25. |
