| 摘要 |
PURPOSE:To prevent occurrence of measuring errors due to contamination of mirrors and the like, by receiving light from a light source through a mirror by detectors, generating signals corresponding to two wavelengths, and computing the ratio of the signals by an operating means. CONSTITUTION:Light from a light source 1 is reflected by a mirror 2 and inputted to detectors 51 and 52 through a light splitting means 3 and filters 41 and 42. A ratio E0 between signals E1 and E2 corresponding to two wavelengths obtained by the detectors 51 and 52 is computed by an operating means 6. A temperature controlling means 7 is controlled by the ratio E0. The mirror 2 is cooled until dew is condensed on the mirror 2. When the dew is condensed on the mirror 2, its reflectivity is largely changed. The signal E1, the signal E2 and the ratio E0 are also changed. At this time the temperature of the mirror is detected by a temperature sensor 8, and a dew point T is obtained. |
