Liquid Flow Meter Calibrations with the 0.1 L/s and 2.5 L/s Piston Provers
Jodie G. Pope, John D. Wright, Aaron N. Johnson, Christopher J. Crowley
This document provides a description of the 2.5 L/s and 0.1 L/s liquid flow calibration standards operated by the National Institute of Standards and Technology (NIST) Fluid Metrology Group to provide flow meter calibrations for customers. The 0.1 L/s and 2.5 L/s flow standards measure flow by moving a piston of known cross-sectional area over a measured length during a measured time. The 0.1 L/s standard uses a passive piston prover technique where fluid is driven by a pump that in turn moves the piston. The 2.5 L/s standard uses a variable speed motor and drive screw to move the piston and thereby move the fluid through the system. This standard is presently operated using a propylene glycol and water mixture that has kinematic viscosity of approximately 1.2 cSt at 21 °C (1 cSt = 1 x 10-6 m2/s) but the ratio of propylene glycol to water can be altered to offer a range of fluid properties. The 0.1 L/s standard has an expanded uncertainty of ± 0.044 % spanning the flow range 0.003 L/s to 0.1 L/s (0.05 gal/min to 1.5 gal/min) and the 2.5 L/s standard has an expanded uncertainty of ± 0.064 % spanning the flow range 0.02 L/s to 2.0 L/s (0.3 gal/min to 31 gal/min) (Here, expanded uncertainties correspond to a 95 % confidence level). In this document, we provide an overview of the liquid flow calibration service and the procedures for customers to submit their flow meters to NIST for calibration. We derive the nist-equation for calculating flow at the meter under test, including the corrections for storage effects caused by changes in fluid density in the connecting volume (due to temperature changes). Finally we analyze the uncertainty of the flow standards, give supporting data, and provide a sample calibration report.