Gas Flowmeter Calibrations with the 34 L and 677 L PVTt Standards

Abstract

This document provides a description of the 34 L and 677 L pressure, volume, temperature, and time (PVTt) primary gas flow standards operated by the National Institute of Standards and Technology (NIST) Fluid Flow Group. These facilities are used to provide gas flowmeter calibration services as reported in NIST Special Publication 250 [Marshall 1998] for Test Numbers 18010C and 18050C. The PVTt standard uses two collection tanks and two diverter valve systems to perform gas flowmeter calibrations between 1 L/min and 2000 L/min (the reference temperature and pressure conditions are 293.15 K and 101.325 kPa). The standard measures flow by collecting gas in a tank of known volume during a measured time interval. The uncertainty of the flow measurement is between 0.02 % and 0.05 % (k = 2 or approximately 95 % confidence level), depending on the gas used and where in the flow range the facilities are being used. We provide an overview of the calibration service and procedures for customers to submit their flowmeters to us for calibration. We describe the significant and novel features of the standard and analyze its uncertainty.