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Title: Comparisons Of Viscous-Sealed Provers With Lne And Studies Of Piston - Cylinder Leakage
Author: Harvey Padden
Source: 2006 Measurement Science Conference
Year Published: 2006
Abstract: Inter-laboratory comparisons DryCal medium and large sized cells had validated our uncertainty analyses for flows above 100 sccm. However, we wished to test the lowest flow range using our smallest cell. LNE (Laboratoire National de Metrologie et dEssais), in Paris, performed a calibration over the complete flow range of 5 to 50,000 sccm using their dynamic gravimetric standard, repeating the tests after six months to test long-term reproducibility (drift). All results of the LNE comparison were favorable. However, at 5 sccm the ML-800-10 cell was near the limit of its allowable uncertainty. Perhaps this was the result of inaccuracies in our calibration of the tare leakage value of the viscous-sealed piston. Therefore, we investigated piston leakage test methodologies, leakages constancy with flow and the ability to predict leakage for varying gas species. We evaluated a number of leakage calibration methods after building a new, 0.25C stability, laboratory. We finally decided upon a successive-inversion technique, with leakage being half the magnitude of the difference between successive upright and inverted readings of flow. We were able to prove that leakage was invariant with flow and to assess the magnitude of error using varying gas species.

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