| 摘要 |
PURPOSE:To contrive to execute a measurement at <=-80 deg. with high accuracy by radiating a condensed light beam, etc. to a part to which gas to be measured has been blown, on the specular surface, in an optical dew-point instrument, and measuring a sudden increase of scattered light generated at the time its reflection. CONSTITUTION:A light beam from a light source 1 is condensed by a parabolic mirror 19 and a convex lens 2, condensed onto a specular surface 4 through an incident window 3, a helium refrigerator 5 is allowed to come into contact with the specular surface 4, and also, a specular surface temperature is controlled by a heater 6 and a temperature controller 7. Also, this device is constituted so that the light beam which is reflected by the specular surface 4 is measured by a photodetecting element 8 installed on an optical path being different from a reflected light path. Subsequently, gas to be measured is led in from an inlet 13, cooled to a little higher temperature than that of the specular surface 4 by a precooler 14, and thereafter, blown from a nozzle 10, cools gradually the specular surface 4, and coagulates water in the gas, and an increase of scattered light is measured, and also, a temperature of the specular surface 4 is measured by a thermocouple 9.
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