Results of the regional key comparison Euromet.M.P-K1.b in the pressure range from 3 × 10^-4 Pa to 0.9 Pa

Abstract

Within the Euromet region a regional key comparison (Euromet.M.P-K1.b) was carried out in order to compare national vacuum standards in the pressure range from 3 × 10-4 Pa to 0.9 Pa. The participants were the BNM-LNE (France), CEM (Spain), IMGC-CNR (Italy), IMT (Slovenia), NPL (United Kingdom), UME (Turkey), and the PTB (Germany) as pilot laboratory. The measurements were carried out from April 2000 to February 2002.Two spinning rotor gauges served as transfer standards and showed a good transport stability. The effective accommodation coefficients of the rotors had to be determined at eight target points at and between 3 × 10-4 Pa and 0.9 Pa. The uncertainty of the generated pressure in the calibration standard was reported as part of the calibration report by each laboratory. All additional uncertainties that were related to the transfer standard were evaluated by the pilot laboratory in order to have a uniform uncertainty analysis for all participants and in order to emphasize the importance of the reported uncertainty of the generated pressure.From the available data a Euromet reference value was calculated at each target pressure. The results from most of the laboratories showed a good agreement with the reference value within the combined uncertainties. A few values of three of the laboratories were significantly off the reference value.At the highest target pressure of 0.9 Pa a linkage to the lowest target pressure at 1 Pa of the key comparison CCM.P-K4 was possible by means of the results of three laboratories that took part in both comparisons.Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCM, according to the provisions of the Mutual Recognition Arrangement (MRA).

Final report of key comparison CCM.P-K3: absolute pressure measurements in gas from 3 × 10−6Pa to 9 × 10−4Pa

“…In addition, there is no clear correlation between changes in a iNISTm at NIST for cycles 1 and 2, to changes in a iPTBm at PTB for cycles 1 and 2; for SRG-027 the changes at PTB were opposite in sign and larger in magnitude than at NIST, while for SRG-030 the changes at PTB were of the same sign and of similar magnitude as at NIST. In an earlier key comparison utilizing SRGs [15], a linear drift model was used to estimate changes in a i using the pilot laboratory calibrations. In that case there was a preponderance of evidence that the calibration ratio of two SRGs was decreasing with time.…”

“…The relative Type A standard uncertainty of each SRG in combination with the primary standard is given by the standard deviation of the mean, corrected for limited sample size [15,17]:…”

“…Past international comparisons using vacuum gauge artifacts have also used repeated measurements at the pilot laboratory during the course of the comparison to characterize the uncertainty due to long-term shifts [11,13,14,15]. One method [11,15] assumes that the pilot laboratory value of a i , at the time of the participant measurement of a i , would be midway between the pilot laboratory value taken before and after the participant measurement. According to this method, an estimate of u LTS (a i ) is taken as one-half of the difference of the before and after values.…”

“…This is further modified by applying the Bayesian correction for limited sample size [15,17]; because two degrees of freedom are lost due to the pooling of the data, the appropriate effective sample size for the Bayesian correction is n b = 5. The relative standard uncertainty due to long-term shifts is:…”

“…These components are calculated in the same manner as for the SRGs, using the standard deviation of the mean corrected for limited sample size [15,17]:…”