Comparison of the high vacuum standard parameters computed from two models

The paper presents the results of analyses of the high vacuum standard obtained with the use of two models: traditional and the new, so-called 'global'. It was found that the assumptions used in the traditional approach i.e. uniform and cosine gas flux density distribution at the orifice plane and the uniform distributions of the gas flux on the calibration and pumping chamber walls, are not fully fulfilled. These effects cause the effective pumping speed calculated with both models to differ and the relative difference equals 4 x 10(-4). Additionally it was found that the uncertainty of the vacuum standard due to the orifice dimensions measurements being imprecisely computed using the global model is twice smaller taking into account the gas beaming effect. (c) 2008 Elsevier Ltd. All rights reserved.