Ultraviolet Hygrometer

An ultraviolet hygrometer has been developed that uses an optical technique to provide fast response, stable calibration, and immunity to airborne contaminants. It is a two-wavelength two-path instrument that relies on the differential absorption by water vapor of two wavelengths in the vacuum ultraviolet. The differential absorption technique employs a reference path and a second wavelength to address the problems of detector drift, changes in lamp output, and window contamination.