Development of a new controlled-clearance pressure balance for hydraulic high-pressure standard

We are developing a new controlled-clearance pressure balance aiming to upgrade the hydraulic high-pressure standard up to 1 GPa. This new pressure balance consists of three parts: (i) a pressure generation device up to 1 GPa, (ii) a weight-loading unit which can load/unload weights automatically and independently, (iii) a controlled-clearance piston-cylinder assembly which is designed to allow the jacket pressure to be applied up to 50 % of the system pressure. In this study, the procedures for in situ mass calibration were developed and the mass of weights was calibrated. The results of the calibration were compared with those performed in 2003. The uncertainty of the mass was reduced compared with that in 2003 because the waiting time before data acquisition was set appropriately. The relative change in the mass was less than 2 ppm (parts per million) and the absolute value of the normalized error, E_n, was less than unity. Thus, it is confirmed that the weight-set is kept in a suitable condition and the mass of them is sufficiently stable.