PURPOSE: To obtain a dew point which is seemed to be the most correct value by a method wherein the intensity of a scattered light is adjusted to be fixed from the maximum value after dew is formed on a reflector, and a temperature at that time is made to be the dew point.
CONSTITUTION: Gas to be measured is introduced from an inlet 5a into a chamber A controlled to be at a prescribed temperature by a heater 8a' and a thermometer 19a' and the gas contacting with a reflector 10a from a hole 9a is introduced into a chamber B through a gap 11a and released from an outlet 6a. While a temperature sensor 19a inserted near the reflector 10a is used, on the occasion, the temperature of the reflector 10a is cooled or heated by a freeze generator 1a and a heater 8a according to a prescribed system, and in a process wherein the reflector 10a is cooled, dew is formed on the surface of the reflector 10a. Thereby the light from a light source 4a is scattered and the intensity of light detection of a detector 2a (4a') with a condenser lens is increased (decreased) by the scattered light. After a maximal point of this scattered light is obtained by a computer, the temperature of the reflector 10a is controlled so that the intensity of the scattered light be fixed, and the temperature at the time when the intensity of the scattered light is kept fixed is made a dew point. Accordingly, recognition of the dew point in subcooling can be prevented and the correct dew point is obtained.
MAKIHARA AKIRA
NAKAMURA HIROSHI
KIKUCHI SHIGERU
HAYASHI SHIGEKI
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