METHOD AND APPARATUS FOR LONG TERM ACCURATE MEASUREMENT OF AMMONIA GAS CONCENTRATION IN A PERMANENT AMMONIA GAS ENVIRONMENT

摘要

A method and apparatus are described for measuring the concentration of a gas with an absorption band in the ultraviolet range. The device includes an absorption chamber containing a gas, a light source, a selected optical bandpass filter, and ultraviolet photodetectors. The gas concentration is measured by the ratio of a transmitted intensity to an incident intensity with the Beer-Lambert Law relation. A second light source may be used for a compensation signal. A second method periodically changes the absorption coefficient by inserting a transparent material in the absorption path to measure the optical compensation signal. A third method periodically shortens the optical absorption path by moving the active detector closer to the light source to measure the optical compensation signal. The fourth method uses an optical element to deflect the optical beam to create a shorter absorption path as a reference for the incident signal using one detector.