Uncertainty analysis of NIST’s 20 liter hydrocarbon liquid flow standard

The National Institute of Standards and Technology (NIST) uses a bi-directional 20 L-displacement piston prover as its primary standard for measuring hydrocarbon liquid flows ranging from 1.86 × 10⁻⁵ m³/s (0.3 gpm) to 2.6 × 10⁻³ m³/s (40 gpm). Our analysis shows that the prover’s uncertainty over this flow range is 0.074 % (k = 2, corresponding to a 95 % confidence interval). Using a dual rotor turbine meter as the transfer standard, we compare the new 20 L piston prover standard with NIST’s other hydrocarbon liquid standards and NIST’s water flow standard. The results are consistent with the presented uncertainty analysis.