Comparison of volume measurements of mass standards at low pressures and in liquids

Abstract

The determination of the volumes of mass standards is key to the precise determination of their masses, due to the effect of the air buoyancy force. The buoyancy force can either be reduced by mass determination at low pressure or enlarged for a determination of the apparent mass using a vessel filled with liquid. The standard method for the volume calibration of weights is comparison in liquid, as described in the document OIML R111. This report presents the results of calibrating the volumes of stainless-steel mass standards with a nominal mass of 1 kg at low pressure and in a liquid. The authors showed that both methods produced comparable results with maximum differences of 0.002 cm3 when adjusted for a standard temperature of 20 °C. The typical uncertainty in the volumes given by both methods is 0.002 cm3. A major source of uncertainty is the volume of the reference weight. The authors conclude that both methods produce consistent results, so that the method of volume calibration at low pressure can be used instead of hydrostatic weighing. The advantage of this approach is that both the masses and volumes of the weights are measured using the same mass comparator, which requires less manipulation. This study will help to establish the procedures for the dissemination and transfer of the mass unit from vacuum to ambient conditions in the institute of the author.