| 摘要 |
PURPOSE:To simplify the constitution of a detecting device, to reduce the member cost, machining man-hours, etc., and to improve the economic efficiency by using one photodetector for both opposite position detection in common as disturbing light detection device. CONSTITUTION:A photosensor 5 is fitted at 90 deg. larger than an angle alpha of incidence, and this sensor 5 detects the opposition interval to a surface 1 to be measured. Then when film thickness is measured, an angle of reflection is the sum of the angle of incidence and + or -60 deg. because the angle of grained screen is up to + or -30 deg.. The angle of a water surface, however, is <30 deg. when water sticks, so the extent of the angle of reflection varies. For the purpose, the angle of incidence on a projector is set to 30 deg. and the angle of photodetection of reflected light is set to 30 deg.. Further, the reflected light measured part of disturbing light is measured at a different angle from a reflected light measurement direction to eliminate the influence of the disturbing light. Then, the measurement position of a plate surface, etc., to the surface 1 to be measured is selected by a supporting mechanism and the opposition interval where the photodetection output of the sensor 5 is maximum is determined; and the difference between the photodetection outputs of the photosensors 4 and 5 is found to accurately measure the liquid film thickness of the water, etc., sticking on the surface 1 to be measured.
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