A Comparison of Primary Gas Flow Standards Spanning the Range 10 sccm N2 to 10 slm N2

We describe an international comparison of gas flow standards spanning the range 2.1 x 10-4 g/s (10 sccm) of nitrogen to 0.21 g/s (10 slm) of nitrogen. For all the participating laboratories, |En| 0.78, where En is the difference between the participant’s result and the comparison reference value divided by the uncertainty of this difference. The k = 2 uncertainties (corresponding to 95 % confidence level) of the comparison reference values range from 0.036 % to 0.052 %. These comparison uncertainties include a contribution of 0.042 % from the uncertainty of the three laminar flow elements used as transfer standards. The participating laboratories were: Laboratoire National de Métrologie et d'Essais (LNE), National Institute of Standards and Technology (NIST), Fluke Primary Pressure and Flow Laboratory, Phoenix Arizona USA (FCP), Èeský Metrologický Institut (CMI), and Physikalisch-Technische Bundesanstalt (PTB).