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Title: Lower Uncertainty (0.015 % To 0.025 %) Of Nists Standards For Gas Flows From 0.01 To 2000 Standard Liters / Minute
Author: John D. Wright, Aaron N. Johnson
Source: 2009 Measurement Science Conference
Year Published: 2009
Abstract: NIST has reduced the uncertainty of its 34 L and 677 L Pressure-Volume-Temperaturetime (PVTt) primary flow standards from 0.05 % to 0.025 % (k 2) for air flow in the range from 0.01 slm* to 2000 slm. Over the restricted range from 0.1 slm to 1000 slm, the uncertainty was reduced to 0.015 %. The reductions in uncertainty were primarily the result of accurately accounting for the water vapor present in the flowing air. Additional uncertainty reductions result from improved measurements of the pressure and of the collection tank volumes. The latter two improvements slightly reduced flow uncertainties for dry gases (e.g., N2, Ar, He, and CO2) from 0.03 % to 0.025 % in the wider range.

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