Evaluation of the conductance of the orifice of the new CNR-IMGC dynamic expander

Abstract

Different methods, based both on analytical considerations and on the Monte Carlo evaluation, were applied to the calculation of the correction factor, , of the conductance of the orifice of the new Istituto di Metrologia "G. Colonnetti" (CNR-IMGC) dynamic system. The results are compared and the uncertainty with which is determined is discussed. The data from the McCulloh method and from Monte Carlo simulations are compared. The latter method, while taking into account the conductance of all the geometrical parts, offers the possibility of evaluating the uncertainty without any approximation.

Comparison of the experimental data and the simulation results of backstreaming effect in the continuous gas expansion vacuum standard

“…The agreement between the measurement and the simulation results is below 0.000 02. The dimensions of the orifice system assumed in the simulations were equal to those measured earlier (see [5]). The dimensional inaccuracy of the orifice system may introduce a systematic deviation of β below ±0.000 06, which was found from separate simulations performed for appropriate orifice dimensions.…”

“…A comparison of the results of the measurements and of the simulation allows us to estimate whether the MC method is really a precision tool suitable for analysing metrological systems. The answer to this question is important, since this method is often used for computing the conductance of the orifice system [5], the gas flux distributions [6], etc.…”

The development of vacuum measurements down to extremely high vacuum – XHV

“…Such devices are, generally, made of a calibration chamber connected to the pumping chamber through a conductance. The pumping system is, frequently, a combination of mechanical and turbo molecular pumps and the conductance is as near as possible to a hole in a thin wall to be able to calculate its value by analytical [98,99] or by Monte Carlo methods [100,101].Those systems need to be equipped with a gas flow generating and measuring unit that is frequently based on the variable-volume and constant-pressure method [102,103]. In the simple realization the lower limit may be between 10-6 and 10-7 Pa. For lower pressure, on the historical point of view it should be mentioned the PTB molecular beam system realized several years ago by G. Messer and G. Grosse [104,95].…”

Global model of the gas flow in high-vacuum standards

“…The possibilities of application of the global model, described above, are limited solely by the calculation capability of the computer employed. A computer program based on [13], supplemented with certain modules designed for the computations according to the idea underlying the global model, has already been developed. Moreover, distributed computations [14], together with the increasing calculation capabilities of computers at present, raise our hopes that the possibility of a substantial broadening of the application range of this model will come soon.…”