International comparison of a NIST primary standard with an NRLM transfer standard for small mass flow rates of nitrogen gas

International comparisons of small gas flow measurements were carried out between the National Institute of Standards and Technology (NIST) in the United States of America and the National Research Laboratory of Metrology (NRLM) in Japan. An NRLM transfer standard package composed of sonic venturis, two pressure transducers, and two temperature sensors was calibrated using the NRLM primary standard for low gas flows (a gravimetric system) and was brought to the US in April 1996. The NRLM transfer standard was compared with the NIST Fluid Flow Group piston provers (a volumetric system) using mass flow rates of nitrogen between 0.4 g/min and 11.5 g/min. The mean differences between the NRLM transfer standard and the NIST Fluid Flow Group piston provers ranged from -0.09 % to +0.13 %.