Uncertainty analysis of the high vacuum part of the orifice-flow-type pressure standard

摘要

The orifice-flow-type pressure standard is commonly accepted as primary standard for vacuum gauge calibration in the high vacuum gas pressure range. It consists of two parts-a high vacuum part and a flowmeter. Practical questions arising at design of the standard have to be answered based on the standard uncertainty analysis.The analysis of the uncertainty sources in the high vacuum part except deviations from the Maxwellian distribution is given in the paper. Uncertainty of a precise flowmeter is taken from references for comparison. It follows from the analysis that uncertainties caused by some sources at routinely achievable parameters are negligibly small and further improvement brings no benefit. The crucial quantities influencing the total uncertainty are the temperature of the chamber and the flowmeter, the outgassing rate from the inner surfaces, the ultimate pressure of the pump and the additional (detrimental) pumping speed. The pumping speed of the main pump has to be "sufficiently higher" than the orifice conductance. (C) 2004 Elsevier Ltd. All rights reserved.