NIST calibration services for gas flow meters: piston power and bell prover gas flow facilities

This document provides a description of the small and medium range gas flow calibration facilities at the National Institute of Standards and Technology (NIST) Fluid Flow Group, as reported in NIST Special Publication 250 [1] for Test Nos. 18010C-18040C and 18050S, Flow Rate Measurements. The Fluid Flow Group can perform gas meter calibrations and special tests at flows between 3.7 x 10"^ mVmin and 1.4 mVmin (0.001 standard cubic feet per minute (scfm) and 51 scfm, reference temperature and pressure are 293.15 K and 101325 Pa) using positive displacement techniques. The flow rate of gas passing through the meter under test is determined from pressure, temperature, volume, and transit time measurements of a displaced volume of gas. Two types of displacement devices are used: mercury-sealed piston provers and bell gasometers, or bell provers. This report describes the techniques used for calibrating meters and presents the uncertainty analysis associated with such calibrations.