| 摘要 |
PURPOSE:To extract even a defect signal whose output variation is equivalent to a noise level with good sensitivity by subtracting the signal of the low frequency component of a detection signal from the detection signal and obtaining the difference signal between the body. CONSTITUTION:At the time of a defect is detected, a magnetic disk 1 is mounted on a spindle 3 provided on a straight moving table 2 and a photoelectric element 6 is scanned by driving motors 4 and 5. Then the detection signal of the element 6 is amplified 9 and then inputted to an A/D converter 10. The converter 10 uses the output signal of a rotary encoder 8 as a clock and converts the detection signal from analog to digital, thereby outputting the converted signal to signal processors 16 and 17. The processors 16 and 17 extracts the low frequency component of the detection signal and calculates the difference between the detection signal and low frequency signal every time the signal is inputted from the converter 10. Then, the absolute value of the integral value of the difference signal is compared with a threshold value setting 18 and only when the threshold value is larger, the absolute value of the integral value of the difference signal is written in a memory 20. At this time, coordinates from counters 11 and 12 are used as position information on the defect.
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