| 摘要 |
PURPOSE: To obtain a scratch tester to secure the stable and constant testing performance against the entire surface to be tested by setting a discriminating threshold value proportional to the standard deviation indicating the changing width of noise. CONSTITUTION: A discrimination threshold calculating circuit 7 calculates a mean value Vav of noise signal on a steel plate 1 based on the light reception signal that is obtained through a high-speed auto gain control circuit 6. Further, it calculates the changing width of the noise signal, that is, a standard deviation Vσ, and it is multiplicated by the preset gain, then the obtained value is added or substrated to/from the mean value Vav, and the resulted value is outputted as a discriminating threshold. The added value is used as a discriminating threshold for the detection of surface defect where the output signal level of an CCS line sensor becomes higher, while the substrated value is used as a discriminating threshold for the detection of surface defect where the output signal level becomes lower. An abnormal part discriminating circuit 8 binarizes the output signal from the sensor through the circuit 6 and extracts the scratch part. |
