| 摘要 |
PURPOSE:To extract a flaw signal with good sensitivity even when the level of a detection signal varies gently and largely as compared with the change of a flaw signal and a noise component is further contained, by calculating the change quantity of an image signal within a definite time and judging a flaw if the absolute value thereof reaches a threshold value or more. CONSTITUTION:A magnetic disc 1 is mounted to a spindle 3 and a photoelectric element 6 is scanned by drive motors 4, 5. The detection signal from the element 6 is amplified by an amplifier 9 to be inputted to an A/D converter 10. Signal processors 16, 17 perform the judgement and renewal of the max. value and min. value of the detection signal and the operation of the difference between both values every time when the signal from the A/D converter 10 is inputted. Then, the absolute value of the change quantity of the detection signals within a gate signal time having a width equal to the size of a flaw generated in a mutually overlapped state through a frequency dividing circuit, an odd circuit 14 and an even circuit 15 is compared with the threshold value set by a thresh old value setting device 18 and, only when said absolute value is larger than the threshold value, the absolute value of the signal change quantity is written in a memory 20 by a writing order 30. |
