Comparison of NPL high vacuum standards SEA2 and SEA5.

This report describes a comparison between two of NPL’s high vacuum pressure standards, SEA2 and SEA5, in the pressure range 3×10-4 Pa to 0.9 Pa, using unbaked spinning rotor gauges as transfer standards. The structure of the comparison and the subsequent data analysis is based on that of the (bilateral) comparison SIM-EUROMET.M.P.BK3 and of the wider comparison, EUROMET.M.P-K1.b in which SEA2 took part. The results demonstrate that SEA5 is equivalent to SEA2 in the measured range and in addition, demonstrates that SEA5 is equivalent to the EUROMET key comparison reference values in the range 9×10-4 Pa to 0.9 Pa.