Improvement of mass standard up to 20 kg by multiple calibration method

Aiming at improving the mass standards, calibrations of standard weights of 1 kg to 20 kg have been performed by using a multiple calibration method. The mass comparisons of standard weights are made by three mass comparators installed in an air-tight chamber. The two automatic mass comparators used for measuring the masses of 2 kg to 20 kg are renewed in their self-centering system of weighing pans to improve the standard deviations of weighing indications. In addition, the lower setting limit of air density in the air-tight chamber is extended down to 0.2 kg/m/sup 3/ from 0.7 kg/m/sup 3/ and the reliabilities of evaluating the mass and the volume of weights are improved. As the reference standards of the multiple calibration method, two 1-kg stainless-steel weights, whose mass and volume are traceable respectively to the prototype kilogram and the silicon density standard, are used.