Bilateral comparison between NIM’s and NIST’s gas flow standards

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A bilateral comparison of the gas flow standards of the National Institute of Metrology (NIM) in China and the National Institute of Standards and Technology (NIST) in the USA was conducted from June 2008 to October 2009. Two critical flow venturis (CFVs) with nominal throat diameters of 10 mm and 20 mm, respectively, were selected as transfer standards. The CFVs were calibrated on NIM’s 20 m3 PVTt system and then on NIST’s 26 m3 PVTt system. The results demonstrate the equivalence between NIM’s and NIST’s gas flow measurement capabilities for flows ranging from 1000 liters per minute to 4000 liters per minute at reference conditions of 101.325 kPa and 293.15 K. The experimental data agreed with existing theoretical models within 0.07 %. All the data agree with the ISO 9300 empirical equation within its 0.3 % expanded uncertainty limit.