Uncertainty evaluation on the fully-automated sub-multiple calibration in the milligram range

The National Metrology Institute of Japan, AIST establishes the mass standards from 1 mg to 5000 kg, referring to the Japanese prototype kilogram, and these standards are disseminated to the weight-calibration laboratories. In this service, calibration of standard weights in the mass range of 1 mg to 500 mg has been performed by using a sub-multiple calibration method. The mass comparisons of standard weights are made by a fully-automatic mass comparator with a capacity of 5.1 g and a readability of 0.1 μg. A new weighing scheme for sub-multiple calibration is presented in order to operate the fully-automatic mass comparator more efficiently. The expanded uncertainty of the mass of the 500 mg weight measured by the sub-multiple calibration method has been estimated to be 1.7 μg. This paper describes the measuring procedure of the sub-multiple calibration by using the fully-automatic mass comparator. The measured results of the sub-multiple calibration of 100 mg decade are also presented.