Towards an optical sensor for air moisture monitoring in mass metrology

In metrology, a mass is measured by comparison with a standard. When calibrating a one kilogram in stainless steel with respect to a standard in platinum-iridium, the correction to the mass difference (about 95 mg) arising from air buoyancy is considerable in regard to the accuracy sought (some /spl mu/g). The main uncertainty on this term is associated with the measurement of air humidity in the chamber of the balance. Experimental observations show that a dew-point hygrometer must be used carefully when the measurement involves a relatively small volume of air. This paper, focus on monitoring water vapour in an enclosure chamber at atmospheric pressure. It give proof of the sensitivity and make advantage of the optical sensor based on molecular absorption, for real-time control of the variations of the air moisture content in mass metrology.