JPS5669537A - Defect inspection device - Google Patents

Abstract

PURPOSE:To detect all the defects effectively irrespective of type of defects or position by differentiating more than once the image pick up signal of an object to be inspected and converting the defect signal into a signal largely changing level into positive and negative. CONSTITUTION:The image pickup signal referring to normal and defect inspection object materials 31, 33 is differentiated and amplified by a differentiating circuits 39, 43 and amplifying circuits 41, 45, and the difference between the above-mentioned signal and the sample holding signal of the sample holding circuit 47 is obtained in the differential amplifying circuit 49. Then, in the comparison circuits 51, 53, it is compared with the respective positive and negative reference levels of the reference level setting circuits 55, 57 to be converted into pulse train signals largely changing in level to positive and negative. Only when the pulse train groups having the pulse signals of the output of the comparison circuits 51 and 53 have both two, they are judged to be normal by a judging circuit 61. In the case where at least one has three or more pulse train groups, the presence of the defect is judged. Thus, a small defect can be effectively detected.