| 摘要 |
<p>PURPOSE:To improve resistance to dust piling by maintaining the output of a photo-electric conversion means in the state without a medium in a maintaining means, remaintaining the output of the photo-electric conversion means in case of lowering of the signal amplitude, comparing the signal amplitude with the output of the photo-electric conversion means and detecting the medium. CONSTITUTION:The light emitted from a light source 1 is photo-electrically converted 2. A maintaining means 3 maintains the signal amplitude of the electric signal converted in the means 2 according to a maintaining command signal SH. This signal amplitude output from a means 2 varies with the existence of a medium or the piled amount of dust on the light path P from the light source 1 to the means 2. A comparison means 4 compares the signal output by the means 2 and the signal amplitude maintained in the means 3. When the signal amplitude output from the means 2 becomes smaller than the signal amplitude maintained in the means 3, a medium detection signal SO indicating the existence of a medium is output. A maintaining signal amplitude lowering detection means 5 compares the signals from means 2 and 3 and outputs signal SH when the signal amplitude of the means 3 becomes smaller. The means 3, in accordance with the signal SH, newly maintains the signal output by the means 2 at the moment.</p> |
