Establishment of an Ultra-High Accuracy 670 PVTt Gas Flow Primary Standard at NMIA

K. Chahine, Z. Wang

Abstract

A new PVTt standard for gas flow has been commissioned at NMIA, which relies on measurements of pressure, volume, temperature and time. The main aim of developing this new standard was to reduce the ±1000 ppm (±0.10%) uncertainty of measurements made with NMIA’s bell and mercury-sealed piston provers. The uncertainty associated with measuring the mass flowrate using the new PVTt standard is estimated to be ±116 ppm (±0.012%), this significant improvement in uncertainty can be attributed to two reasons. Firstly, the volumes of existing provers at NMIA were measured to no better than ±400 ppm, whereas the volume of the new PVTt standard has been determined gravimetrically using water with an uncertainty of ±80 ppm. Secondly, existing provers are used in ambient air with a spatial temperature uniformity of 150 mK, while the new PVTt standard is immersed in a temperature controlled water tank with a temperature uniformity of 2 mK. In this paper, a description of the PVTt standard is presented. A comprehensive uncertainty analysis is also made and an example calibration is described.

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IMEKO TC

TC9 - Flow Measurement

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