IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Vacuum Science & Technology Thursday Sessions
       Session VST-ThM

Paper VST-ThM9
Some Consideration About Uncertainty on the Primary Vacuum Measurements

Thursday, November 1, 2001, 11:00 am, Room 125

Session: Pressure & Flow Measurement Instruments & Their Calibration
Presenter: A. Calcatelli, Consiglio Nazionale delle Ricerche, Italy
Authors: A. Calcatelli, Consiglio Nazionale delle Ricerche, Italy
M. Bergoglio, Consiglio Nazionale delle Ricerche, Italy
Correspondent: Click to Email
The need of better characterisation of high quality gauges in the various vacuum ranges represents a considerable input to accurate analyses of the available primary systems. That was connected to the need of defining ranges and related uncertainties for the international comparisons. The uncertainties of the IMGC systems are discussed. Static system: the measurand, p@subi@,is given by p@subi@=p@sub0i@R@subj@T@subV@/T@subv@ where the quantities p@sub0i@, T@subv@, T@subV@ and R@subj@ represent respectively inlet pressure values, the temperatures of the involved volumes and the expansion ratio between the considered volumes. These quantities are generated by several other factors. The input quantities for R@subj@ are correlated since the method is based on the accumulation of the gas inside one of the involved volumes and consequently on sequential measurements of set of pressures. In turn R@subj@ is correlated to p@sub0i@. The covariance matrix is taken into account for the evaluation of the final p@subi@ uncertainty. Dynamic system: the measurand, p@subi@, is given by p@subi@=(Q@subi@/S@subeff@)F@subci@ where the quantities Q@subi@, S@subeff@, F@subci@ represent the values of the gas-flow-rate at pressure p@sub i@, the effective pumping speed at conductance level and the temperature correction factor. These factors are related to several other input quantities. S@subeff@(C/(1+C/S@subp@) is a function of the conductance C and of the pumping speed through the ratio C/S@subp@. C is modelled mathematically and C/S@subp@ is measured in a separated experiment and is periodically checked. Q@subi@ is generated and measured at each desired pressure p@subi@ in the calibration chamber and depends on several quantities. F@subc@, related to the temperatures in the calibration chamber and in the flow-meter is also measured at each pressure level. The uncertainty of both the systems is discussed taking into account the possible correlation among all the considered quantities.