| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To provide a photoelectric sensor and a wafer detector reliably detecting a light transmissive object to be detected. <P>SOLUTION: In a non-detection state, a first threshold Th1 having a large margin is compared with a photoreceptive volume level to be successively taken in. With a case when the photoreceptive volume level is smaller than the first threshold Th1 as a trigger, the detection of a wafer W is determined, based on the comparison with a second original threshold Th2. And the first and second thresholds Th1, Th2 are set, on the basis of the average value of 255 or 235 photoreceptive volume levels taken in immediately before. <P>COPYRIGHT: (C)2006,JPO&NCIPI</p> |
