The optical surface is the key element of the sensor cell and
comprises an acid etched, semi-matt surface with a central
conical shaped depression. A collimated beam of visible red
light is focussed onto the central region of the optical surface to
form an annulus ring of light.
Optical detection is made of light
dispersed. As the sensor is cooled during measurement cycle,
hydrocarbon condensates form on the optical surface and its
optical properties are modified - the reflected light intensity of
the annulus ring increases and there is a dramatic reduction in
the scattered light intensity within the dark spot region.
This highly sensitive secondary effect is used to determine the
hydrocarbon dew point.
