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Abstract

The dual path ultraviolet hygrometer makes use of two narrow spectrum light beams of different wavelengths, both of which are transmitted along two geometrically similar paths to measure and compensate for the presence of contaminants and to more precisely measure the water vapor content in the air samples. A first one of these optical wavelengths is highly absorbed by water vapor while the second optical wavelength is only slightly absorbed by water vapor. Both of these generated narrow band light beams are split so that two pairs of light beams are produced. Beams of both wavelengths are transmitted along the first optical path, which traverses the air sampling chamber. By measuring the differential absorption between the two light beams along this first optical path, the water vapor content of the air sample within the air sampling chamber is precisely measured by correcting for contaminant absorption. The second beam of each pair of each wavelength is transmitted along a second optical path, which is geometically similar to the first optical path to measure the strength of each source. By measuring the differential and received intensities of the two sets of light beams, the level of contaminants in the air sampling chamber for both of the light beams can be determined, since the second wavelength is subject primarily to contamination. Therefore, the contamination in the air sampling chamber can be individually compensated at both of the wavelengths to obtain water vapor concentration measurements of greater precision.

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