Temperature Characterization in the Collection Tank of the NIST 26 m(3) PVTt Gas Flow Standard

Published

September 1, 2003

Author(s)

Aaron N. Johnson, John D. Wright, Michael R. Moldover, Pedro I. Espina

Abstract

Gas temperature gradients created during the filling stage of a PVTt (Pressure-Volume-Temperature-time) calibration cycle, and those imposed by inhomogeneous room conditions, lead to uncertainties in the average gas temperature in the collection tank. Because this temperature plays an important role in obtaining accurate flow measurements, NIST upgraded the temperature-averaging scheme used in our 26 m³ PVTt system. Instead of arithmetically averaging 10 thermistors to obtain the mean gas temperature, this value is now calculated via a volume-weighted trapezoidal integration procedure using 35 thermistors. Applying the new temperature-averaging scheme, the mean gas temperature can be determined to better than 88 mK after only 2700 seconds of fan mixing. As a result, the flow uncertainty in the NIST 26 m³ PVTt system has decreased from 0.22 % to 0.13 % (with a coverage factor of 2).

Citation

Metrologia

Volume

40

Issue

No. 5

Pub Type

Journals

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Keywords

carbon dioxide, critical nozzle, relaxation, sonic nozzle, sonic venturi, sulfur hexafluoride

Citation

Johnson, A. , Wright, J. , Moldover, M. and Espina, P. (2003), Temperature Characterization in the Collection Tank of the NIST 26 m(3) PVTt Gas Flow Standard, Metrologia, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=830800 (Accessed October 26, 2025)