| 摘要 |
PROBLEM TO BE SOLVED: To precisely detect a dust amount contained in the air. SOLUTION: An optical disk 2 worked to make dust easily deposited on its surface is rotation-driven to make the surface of the optical disk 2 irradiated with a laser beam using an optical system 3. Since an integrated value computed by a micro-computer 12 is brought into a low value compared with that deposited with no dust because a level of the reflected laser beam is lowered in a portion deposited with the dust in the surface of the disk 2, a difference between the integrated value and a preset reference value is found to measure the dust amount in the air.
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