Novel method for determining the center of gravity height of mass standards

Abstract:
The most precise vacuum mass comparators have a resolution of 0:1 mug, operating at one kilogram. The resolution represents a relative difference in weight of the artifacts of 1 x 10^-10. Small deviations in the height of the center of gravity of the mass artifacts lead to a systematic error of the measurement results. For example a difference in the height of the center of gravity of 1 cm in Earth’s gravitational field causes a relative systematic uncertainty contribution of 3:2 x 10^-9. Therefore, it is important to know the artifacts’ heights of the center of gravity. This paper introduces a novel approach to measure the height of the center of gravity of high-sensitive mass artifacts. The method allows to compare the mass of artifacts of unusual shape, inhomogeneous composition or hollow mass standards with uncertain internal geometry. For the determination, the mass artifacts are placed on three load cells, arranged at an angle of 120deg. The load cells are attached to the base, which stands on a high-precision tilt table. The difference in force with variation of the inclination angles allows to calculate the height of the center of gravity of the artifacts. To verify the method, various mass standards of known geometry and composition are measured as described. In the end, the comparison between theoretically determined values and the measurement results shows a good agreement of the method.