Volumetric Gas Flow Standard With Uncertainty of 0.02% to 0.05%

[+] Author and Article Information
John D. Wright, Michael R. Moldover

Aaron N. Johnson

Process Measurements Division, Chemical Science and Technology Laboratory, National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, MD 20877

Akisato Mizuno

Department of Mechanical Engineering, Kogakuin University, Nakano-Machi 2665, Hachioji-shi, Tokyo 192-0015, Japan

J. Fluids Eng 125(6), 1058-1066 (Jan 12, 2004) (9 pages) doi:10.1115/1.1624428 History: Received November 15, 2002; Revised June 04, 2003; Online January 12, 2004
Copyright © 2003 by ASME
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Relative difference in the discharge coefficient of critical flow venturis calibrated on both the 34 L (Cd34) and 677 L (Cd677) flow standards versus flow and the inverse of the collection time for the 34 L tank. Also plotted is a linear best fit of the data.
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The chain of measurements and equations used for the PVTt flow standard. The subcomponents are labeled with their relative standard uncertainty ×106 (k=1) for the 677 L system. The mass flow uncertainty is a k=2 or approximately 95% confidence value.
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The time correction for the 34 L tank versus the time relative to the trigger signal indicating bypass valve closure
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Superimposed inventory data traces for a start diversion and a stop diversion in the 34 L tank at 25 slm demonstrating “symmetric” diverter valve behavior. The start dead-end time was approximately 50 ms; the stop dead-end time was approximately 15 ms longer.
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Experimentally measured data (25 slm, 34 L collection system) and predictions for zero and nonzero sensor time constants. The predictions demonstrate that neglect of the sensors’ response times would cause significant error in the measurement of inventory conditions.
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Data from the pressure sensor in the inventory volume during a PVTt flow measurement, showing the transients that occur during the dead-end intervals
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The collection tank pressure and the water bath temperature immediately following a tank filling, 25 slm in the 34 L tank
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Schematic diagram of the PVTt collection tanks, water bath, duct, and temperature control elements
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Arrangement of equipment in the PVTt system




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