Final Report on EUROMET Project 881/EURAMET.M.P-K7: High pressure comparisons between seven European National Laboratories Range 50 MPa to 500 MPa

An inter-comparison in the high oil pressure range was arranged in 2005-2007. The participating laboratories were CMI/Czech Republic, Metas/Switzerland, MIKES/Finland, NMi-VSL/The Netherlands, PTB/Germany, SMD/Belgium and SP/Sweden. CMI, Metas, NMi-VSL and PTB are pressure laboratories of the primary level, and the three others are traceable to LNE/France. The transfer standard was a Desgranges & Huot piston-cylinder unit with a nominal effective area of 1,96 mm², mounted in a D&H 5316 balance body. The participants determined the effective area at ten nominal pressures from 50 MPa to 500 MPa in steps of 50 MPa. All the results were in a good agreement with the reference values, calculated as weighted means of the results from the four primary level laboratories. The results fully support the uncertainties claimed in the CMC tables of the participants. As the pressure distortion is the dominating source of uncertainty in this range, the claimed uncertainties were highest at 500 MPa, ranging from 5,6 · 10^-5 of PTB to 1,2 · 10^-4 of MIKES (expanded relative uncertainties, k = 2). Except for PTB, there were no big differences in the claimed uncertainties between the primary and the secondary level laboratories. Some of the participants underestimated the uncertainties when giving their results in terms of the effective area at null pressure S0 and the pressure distortion coefficient, λ. The uncertainties given by some others were unnecessarily high. The transfer standard was not as stable as expected, and the uncertainties of the reference values were to some extent increased by the observed drift. The comparison, registered as EUROMET Project #881, was started as an informal one between MIKES, Metas, NMi-VSL and CMI, and in the beginning the rules for EUROMET comparisons were not strictly followed. No links to other comparisons were made as the latest EUROMET key comparisons in the high pressure range were carried out more than twelve years ago. Linking will be made as soon as results from newer comparisons are available.