Patent ID: 8172457

Claim:
Sensor for determining the hydrocarbon dew point in a gas, comprising: a transparent body ( 10 ) with a planar measurement surface ( 13 ), a roughened condensation surface ( 12 ) provided on the planar measurement surface ( 13 ), and a back ( 19 ) having a back portion opposite the roughened condensation surface ( 12 ), the roughened condensation surface ( 12 ) providing a surface for the condensation of a gas applied thereto and having a condensation-dependent reflectivity, and the back portion being provided with a reflecting coating ( 46 ), a light source ( 31 ) for emitting a pencil of light ( 1 ) to the condensation surface ( 12 ) at an incident angle selected to cause the pencil of light ( 1 ) to be reflected back and forth several times between the condensation surface ( 12 ) and the reflecting coating ( 46 ) before a final reflection off the condensation surface ( 12 ) and into the transparent body ( 12 ), a light detector ( 34 ) positioned to detect the pencil of light ( 1 ) reflected back into the transparent body ( 10 ) by the condensation surface ( 12 ), for determining the light intensity of the pencil of light ( 1 ) reflected back into the transparent body ( 10 ) by the condensation surface ( 12 ), means for adjusting the temperature of the condensation surface ( 12 ) and an evaluating unit in signal connection with the light detector ( 34 ), wherein the evaluating unit is set up so that when there is at least one of an intensity increase of the light reflected back with decreasing temperature of the condensation surface ( 12 ) and an intensity decrease of the light reflected back with rising temperature of the condensation surface ( 12 ), the evaluating unit determines the corresponding temperature of the condensation surface ( 12 ) and reads out the temperature of the condensation surface ( 12 ) as a measure for the dew point temperature.