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A multi-opening orifice is a device for the primary measurement of gas flows and related vacuum quantities. This device maintains a constant molecular flow regime and thus the possibility to very accurately calculate the conductance from the geometrical dimensions for relatively high pressures, and the value of the conductance is sufficiently high to achieve reasonable parameters of the vacuum system...
Gas flow through an orifice can be determined with high accuracy based only on the geometrical dimensions of the orifice and the upstream and downstream pressures when the flow is purely molecular. An orifice with a number of smaller openings in parallel can be used to maintain the molecular flow at higher pressure and high total conductance of the orifice. The question of how close such openings...
Construction of constant-pressure gas flowmeters utilizing directly driven bellows and diaphragm bellows as volume displacers were described in recent decades. They have important advantages: accuracy, reliability, easy operation and maintenance.Difficult is to scale sufficiently accurately the changes in volume at compression, to evaluate the uncertainty of this measurement, and to include all the...
The main obstacle in the construction of primary vacuum standards for very low pressures – ultra-high vacuum (UHV) – is outgassing from the walls of the apparatus. Thus, principles utilising a higher pumping rate in the calibration chamber, e.g., the pressure ratio technique, seem to be more useful for this range. However, a serious problem is inherent in this method, namely, that the gas in the calibration...
Accurate calibrations of gauges to ever lower pressures (higher vacuum) are increasingly becoming necessary. The calibrations over the entire ultra high vacuum (UHV) range i.e. up to 10−10 Pa are already sometimes demanded by the users of vacuum measuring devices. Standards covering part of this range are available in some national metrological laboratories while primary standards covering the entire...
Continuous oscillations of the pressure of hydrogen and some other gases were observed in an ultra high vacuum (UHV) apparatus. The oscillations arose progressively during experiments with hydrogen permeation through stainless-steel ion-implanted samples, later they occurred in the apparatus without any sample as well. They were observed for a long time, detected with an ionisation gauge and a mass...
The effective pumping speed for particular gas species has to be known in a vacuum system for measuring the absolute amount of this gas. The effective pumping speed for hydrogen during measurements of permeation can be readily determined, usually with sufficient accuracy, if the apparatus is equipped with a device enabling sudden reduction of pumping speed. This process is described.
The orifice-flow-type pressure standard is commonly accepted as primary standard for vacuum gauge calibration in the high vacuum gas pressure range. It consists of two parts-a high vacuum part and a flowmeter. Practical questions arising at design of the standard have to be answered based on the standard uncertainty analysis.The analysis of the uncertainty sources in the high vacuum part except deviations...
The viscosity vacuum gauges are based on the gas momentum transfer phenomena between a moving part of the gauge and a stationary surface. Thus, they may be used for the study of the momentum accommodation coefficient for various combinations of gas species and surfaces. The aim of the present work is to determine the momentum accommodation coefficient by means of the viscosity vacuum gauge with vibrating...
The aim of the present work was to study the dependence of calibration curves of the Becker friction vacuum gauge operated in the decremental mode on the kind of the gas (i.e. on its molecular mass). The calibration curves were measured over the range from 10 -1 Pa to atmospheric pressure for the noble gases (He, Ne, Ar, Kr, Xe) and for N 2 . The theoretical model of the damping...
The need to know the pressure in relatively large vacuum chambers arises at different measurements (calibration of the vacuum gauges, out-gassing measurements, TDS, etc.). Although the uniformity of the gas pressure over some areas in the chamber is crucial for the accuracy of the measurement, it is checked mainly by means of theoretical computations. The experimental determination of the pressure...
A calibration apparatus where the pressure is generated dynamically was designed for the pressure range (10 -5 -10 2 )Pa. It is pumped by a combination of a turbomolecular pump (TMP) and a rotary vane pump. It is easy to control the generated pressure by controlling the calibration gas throughput by means of a precise variable leak valve up to the pressure of approximately 1Pa...
Various friction vacuum gauges were developed in the past. When electronically driven they were usually operated in continuous mode, because the electronics is easier. Present electronics enables operation in the decremental mode as well, thus extending the measuring range. This paper reports operation of Becker's vibrating ribbon gauge in the decremental mode. The vibration of the ribbon was excited...
In the course of experimentation with uhv systems it was observed that there was outgassing of the metal sample caused purely by deformation without action of another body. At first a stainless steel bellows was used to study this phenomenon. Further investigation was carried out with a device consisting of a metal tube connected to a vacuum system. The other end of the tube was rotated through a...
A combination of the reflection high energy electron diffraction (RHEED) and electron stimulated desorption ion angular distribution (ESDIAD) methods has been used as a probe of supported particle morphology and crystallographic structure. It has been shown that these techniques can be used as a tool for in situ investigation of model catalysts prepared by molecular beam epitaxy. The Pd particles...
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