| 摘要 |
PURPOSE:To measure the thickness of a film with high accuracy without being affected by the reflection factor, surface roughness, etc., of a steel plate by irradiating an organic film formed on the surface of a steel plate with an infrared ray having three wavelengths and detecting the energy of its reflected light beams. CONSTITUTION:The infrared ray A from a light source 2 passes through a rotary sector 5 to illuminate the steel plate 1 with the film. Its reflected light beams are divided into three through a 2/3 transmission mirror 8 and a half-mirror 11 and they are detected 10, 13, and 15 through interference filters 9, 12, and 14 respectively and then supplied to a film thickness computing element 16. The filters 9, 12, and 14 extract a wavelength lambda1 of infrared absorption and wavelengths lambda2 and lambda3 of no infrared absorption and they have a relation lambda2+lambda3=2Xlambda1. Light beams B reflected by the sector 5, on the other hand, illuminate a reference plate 6 formed of the same material with the organic film on the steel plate 1 to specific thickness and its reflected light beams are divided into three similarly to detect their light intensity values and then supplied to the computing element 16. The computing element 16 computes the film thickness of the organic film 1b on the steel plate 1 on the basis of those six input signals and the film thickness of the reference plate 6.
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