Assessment of Reproducibility and Linearity of the NMIA Bell Prover Using a High Flowrate Sonic Nozzle Array |
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| Khaled Chahine, Mark Ballico |
- Abstract:
- Critical flow Venturi, or sonic, nozzles are widely used in gas flow metrology as stable and convenient transfer standards. Once the nozzle coefficient has been determined by calibration against a primary standard, the mass flowrate can be determined by knowledge of the upstream gas composition and its pressure and temperature. As these can be determined with great precision, the mass flow achieved can be more reproducible than the nozzle calibration. At NMIA, sonic nozzles used to cover the range 1 to 25 m³/h are calibrated against a bell prover, with an uncertainty of 0.13 % (k = 2). Calibration of the nozzles in additive combination, using a sonic-nozzle array developed at NMIA, allows estimation of the non-linearity of the bell prover primary standard at its maximum flow. In this paper, extensive measurements of the reproducibility of the bell prover calibration of sonic-nozzles are used to identify correlated uncertainty terms in the nozzle calibration, which in turn used to assess the non-linearity as 0.07 % for the highest flows, with a reduced standard uncertainty of 0.015 %.
- Keywords:
- Gas Flow, Bell Prover, Uncertainty Analysis, Sonic Nozzle Array, Linearity, Reproducibility
- Download:
- IMEKO-TC9-2010-003.pdf
- DOI:
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