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Title: Uncertainty Analysis Of A High-Speed Dry Piston Flow Prover
Author: Harvey Padden
Source: 2002 International Symposium on Fluid Flow Measurement
Year Published: 2002
Abstract: This paper discusses a novel high-speed piston prover that uses a clearance seal to achieve very low uncertainties. We will review the instruments design and provide an uncertainty analysis for three sizes of our internal reference provers, designed for flows of 10 ml/min to 50 L/min. Their expanded single-reading uncertainties at 2X coverage range from 0.064% to 0.073%. The instrument also has the capability to average a number of readings, potentially reducing the above uncertainties by a significant amount. Traditional constant-displacement piston provers utilize mercury piston seals and low piston velocities. They have long been used as primary calibration devices for gases at low flow rates. Our design is based on our DryCal production design and it eliminates the seal. The attraction of such a device is its combination of primary (dimensionally-based) flow measurement, simplicity and high speed and small size. However, this instrument has unique uncertainty sources that must be analyzed and controlled. Uncertainty considerations for such a device include (among others) piston leakage, precise characterization of measured volume and the dynamics of a high-velocity underdamped free piston. Fortunately, the high speed of the device and the availability of a stable flow source allow sufficient data for a Type A analysis of the most significant uncertainties (75% to 88% of total u2).

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