Stability of pressure generated by hydraulic pressure balances in NMIJ

To use a pressure balance effectively in the calibrations or experiments, the generated pressure should be kept stable for an adequate time interval. In this study, two characteristics, the short-time stability of the generated pressure and piston fall-rate, are investigated for several free-deformational piston-cylinders and controlled-clearance piston-cylinders currently used in NMIJ. A comparative method using precise pressure transducers is successfully applied to the evaluation. For free-deformational piston-cylinders, the two characteristics largely differ depending on respective piston-cylinders, and there is no strong correlation between these two characteristics. Controlled-clearance piston-cylinders with higher jacket pressure show preferable features; the lower piston fall-rate and smaller short-time fluctuations of the generated pressure. The evaluation method in this study provides information about short-time stability, which is useful to extensively characterize the piston-cylinder used in calibrations.