APPARATUS FOR INSPECTING SURFACE FLAW

PURPOSE:To perform the detection of a surface flaw with good accuracy by removing noise generated instantaneously, by detecting the same position of a material to be inspected at a definite time interval using two sets of infrared detectors. CONSTITUTION:Two sets of infrared detectors 8a, 8b are mounted to the hollow rotor 10 of a rotary mechanism part on the same straight line, and first and second logarithmic operators 16a, 16b performing the logarithmic operation of the outputs of said detectors 8a, 8b, first and second memories 17a, 17b for storing the operation results of said operators 16a, 16b and a subtractor 18 for subtracting the value of the memory 17b from that of the memory 17a are mounted. Two sets of the same infrared detectors 8a, 8b are used on the same straight line and take out the signal level values at the same position when detect infrared rays so as to provide certain definite time difference, and positive and negative threshold values are provided to the difference between logarithmic value and, if the signal level values are equal to, more than or less than the threshold values, said signal level values are removed as abnormal values. By this method, instantaneous noise can be removed and normal values are averaged to be compared with the quantity capable of being judged as a flow preset to a flaw judge device 20 to make it possible to judge the presence of the surface flaw with good accuracy.