| 摘要 |
PROBLEM TO BE SOLVED: To eliminate a delicate positional regulation of a distance between a water level in installing a device and a sensor and to always stably continuously automatically measure an oil film by adopting an optical guide having a plurality of parallel optical paths as an optical path limiting means. SOLUTION: As an optical path limiting means, an optical guide 16 having (3×5)pieces of cylindrical holes each having a diameter of 2 mm in an optical axis direction is used. Thus, a reflected light reflected at a given angle from a water surface 4 is passed through any of a plurality of optical paths of the guide 16, and can be received by the guide 6 even when a distance between the surface 4 and a sensor 13 is deviated at about±5 mm. Accordingly, a delicate regulation of the distance between the surface 4 and the sensor 13 is eliminated. In a surface floating type device, even when the distance between the surface 4 and the sensor 13 is changed at about±5 mm due to an aging change such as an increase in a weight of the device caused by a dirt or a snowfall or a reduction in a buoyancy caused by a deterioration of a float, the reflected light reflected at the predetermined angle is passed through any of the paths of the guide 16. Thus, a stable measurement of an oil film 3 for a long period can be performed.
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