EFFECT OF COVARIANCES IN A DENSITY MEASUREMENT OF SILICON SAMPLES BY HYDROSTATIC WEIGHING

Abstract: A density standard realized by 1 kg silicon spheres has been used for measuring the density of solid samples by hydrostatic weighing. Details are given for the structure of the measurement system, procedure for the solid density measurement, and uncertainty evaluation. The density of a 1 kg silicon sample has been measured with a relative combined standard uncertainty of 1.2 parts in 107. When the effect of covariances in input quantities is taken into account, the relative combined uncertainty in measuring the density difference between the silicon spheres and the silicon sample may be reduced to 3.6 parts in 108. Uncertainty sources in the hydrostatic weighing and the effect of covariance in the input quantities are discussed