Performance evaluation of a mass comparator with a readability of 0.1 μg

In order to achieve higher accuracy of the mass standard in the mass range equal to or less than 100 g, it is necessary for a mass comparator in the range to have a relative sensitivity of the order of 1 × 10^-9. For this purpose, a 111 g capacity fully-automatic mass comparator has been renovated so that its readability is improved from 1 μg to 0.1 μg. The mass comparator is also installed in an air-tight chamber originally developed by the NMIJ, so that it can be kept in stable environment, especially in the air of constant density. With these renovations, standard deviation of the mass comparisons is reduced and uncertainty of the air buoyancy corrections is lessened. This paper outlines the renovations of the mass comparator and shows its improved performance.