Partial differentiation of air density in mass metrology

Abstract

There are four major uncertainty components to be considered when performing mass comparisons. They are uncertainties of weighing process, reference weight used, air buoyancy, and mass comparator. The systematic effect of air buoyancy can be greatly reduced if the air density and the densities of the test and reference weights are known. This paper will emphasis on the uncertainty due to air buoyancy correction only. To calculate the uncertainty of air density correction, partial derivatives of temperature, barometric pressure and humidity must be performed. In this paper, two methods for partial differentiation of air density components are discussed.