PRIMARY AND SECONDARY VACUUM MEASUREMENTS

Primary, transfer and working instruments and systems for pressure det ermination from the barometric range down to low pressures are examine d on the basis of the measurement uncertainty level attained at IMGC. In low-pressure primary measurements over the 10(5)-10(2) Pa range, re lative uncertainties from +/- 1.5 x 10(-5) to +/- 1 X 10(-2) can be ob tained. At lower pressures a relative uncertainty of a few parts in 10 (3) is considered satisfactory; it increases to 10(-2) for 10(-5) Pa p ressures. Calibration results concerning transfer gauges, as well as s hort- and long-term repeatability of the most widely used working gaug es are reviewed.