| 摘要 |
<p>PROBLEM TO BE SOLVED: To set a threshold level in following to a level even when the input level is fluctuated due to an environmental change or the like in the case of discriminating the input level. SOLUTION: A light is emitted from a light projection section 2 for each prescribed period and its reflected light is received by a light receiving section 3. The light receiving signal is A/D converted and discriminated by a discrimination means 13. In this case, the discrimination result and input level are stored in a data storage means 14. When a prescribed number of data is stored, a threshold level calculation means 15 discriminates each distribution of the discrimination result and calculates the threshold level to be an intermediate distribution level. Thus, the calculation processing of the threshold level is conducted stepwise so as to continue the light projection and discrimination for a prescribed period.</p> |
