Skip to main content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.


The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Lower Uncertainty (0.015 % TO 0.025 %) OF NIST S Standard For Gas Flows From 0.01 TO 2000 Standard Liters/Minute



John D. Wright, Aaron N. Johnson


NIST has reduced the flow uncertainty of its 34 L and 677 L Pressure-Volume-Temperature-time (PVTt) primary flow standards from 0.05 % to 0.025 % (k = 2) for air in the flow range from 0.01 slm* to 2000 slm. Over the restricted flow range 0.1 slm to 1000 slm, the uncertainty is 0.015 %.The reduction in uncertainty is 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.
Proceedings Title
Measurement Science Conference Proceedings
Conference Dates
March 16-18, 2009
Conference Location
Anaheim, CA


Critical Nozzle, Flow, Gas, Uncertainty, PVTt.
Created March 23, 2009, Updated February 19, 2017