| 摘要 |
PURPOSE:To improve judging accuracy of the result of the check, by differentially overlapping the signals received by light sensors through low pass filters having different cutt off frequencies. CONSTITUTION:In the vicinity of a material to be checked 10, the light sensor 11 is moved back and forth. The light signal from the sensor 11 is transduced into an electric signal and amplified by photoelectric transducers 16 and 17. The cut off frequencies of the low pass filters 27, 28, 29, and 30 are set so that they are higher or lower than the frequencies corresponding to the rotary speed of the material to be checked 10. The outputs from said pairs of the filters are inputted into differential amplifiers 31 and 32 as differential inputs. Waveform shaping circuits 33 and 34, which are operated at specified levels, are sequentially provided. In this way, the first detected signal is formed. Waveform shaping circuits 35 and 36, which are operated at specified levels, are separately provided for the photoelectric transducers 16 and 17, and the second detected signal is formed. Logic circuits 37 and 38, which receive said second and first detected signals, are provided. |
