Usage history of three mass comparators in the past 20 years
Since March 1996, three mass comparators have been used for mass calibrations of class E1 and E2 weights ranging from 10 g to 10 kg at National Metrology Institute of Japan (NMIJ). These mass comparators are each equipped with four-position weight exchangers and carry out fully-automated mass comparison with relative sensitivities from 10-9 to 10-7. The mass comparisons among four weights, including repeated measurements, take a measuring time of 8 h or longer, so a series of mass comparisons can be made only once a day. Over about 20 years, at least 1700 mass comparison series for each of the three mass comparators and more than 5700 series in total havebeen performed. This paper describes the usage history of the mass comparators during the period from 1996 to 2016, along with some measures taken to maintain and improvetheir reliability.
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