A study of uncertainties at calibration of vacuum gauges

A primary calibration system for calibration of vacuum gauges from atmospheric pressure down to 10 −5 Pa was built several years ago. The pressure generation in the calibration system in the range from 10 −1 to 10 −3 Pa by a dynamic expansion method is described with stress on long term stability (over 7 years) and on the calculated uncertainties. The two chamber vacuum system is coupled through an orifice in a thin plate with calculated conductance. The gas flow is determined by a porous plug of sintered silicon carbide which separates the high and the rough vacuum chamber. Detailed analysis of uncertainty of all influential quantities is presented. The measurements after several years are compared.