Aaron N Johnson et al 2003 Metrologia 40 211 doi:10.1088/0026-1394/40/5/301
Aaron N Johnson, John D Wright, Michael R Moldover and Pedro I Espina
Show affiliationsGas temperature gradients created during the filling stage of a pressure–volume–temperature–time (PVTt) calibration cycle, and those imposed by inhomogeneous room conditions, lead to uncertainties in the average gas temperature in the collection tank. Because these temperature uncertainties dominate the overall flow uncertainty, NIST upgraded the temperature-averaging scheme used in its 26 m3 PVTt system. Instead of arithmetically averaging 10 thermistors to obtain the mean gas temperature, we now calculate this value via a volume-weighted trapezoidal integration procedure using 35 thermistors. Applying the new temperature-averaging scheme, the mean gas temperature can be determined with a standard uncertainty of 89 mK after only 2700 s 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). This paper highlights the temperature improvements and presents a detailed analysis for estimating the lower temperature uncertainty.
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
Issue 5 (October 2003)
Received 22 January 2003
Published 2 September 2003
Aaron N Johnson et al 2003 Metrologia 40 211
Rogerio T Ramos et al 2001 Meas. Sci. Technol. 12 871
M Lightman et al 2006 J. Phys.: Conf. Ser. 32 58
Li Qin et al 2008 Chinese Phys. B 17 726
Ryutaro Takahashi et al 2002 Class. Quantum Grav. 19 1599
M A Shahzamanian et al 2007 Supercond. Sci. Technol. 20 640
Jinliang Xu et al 2005 J. Micromech. Microeng. 15 1344
Bruce I Cohen et al 1998 Plasma Phys. Control. Fusion 40 75
A J M Medved 2005 Class. Quantum Grav. 22 133
M A Doncheski and R W Robinett 2000 Eur. J. Phys. 21 217