Static Expansion System Research Articles

Ensuring primary realization of pressure unit in the vacuum range without typically utilized static expansion system

After the break-up of Czechoslovakia in 1993 the primary metrological standards authority almost fully remained in Slovakia. So we had to build our primary vacuum metrology anew. But we could do it using uptodate techniques that are more effective and they enable us to fulfil our task more effectively and in a shorter time. The steady demand to widen the lower pressure range and a steady demand for maximal accuracy collide with the financial possibilities open to a small country. So it is impossible to follow the classical pattern for the vacuum standards: liquid columns, static expansion system and dynamic expansion system. But it is possible to utilize contemporary progress in construction of piston manometers. This enables us to discard liquid column and static expansion techniques in favour of piston technique [Tesar J, Prazak D. Vacuum 2002; 67: 311, Tesar J, Prazak D, Krajicek Z. In:Proceedings of international symposium on Pressure and Vacuum, 2003. p. 169, Tesar J, Repa P, Prazak D, Krajicek Z, Peksa L. Vacuum 2004; 76: 491.]. Such system fulfils all the needs of a little industrial country and is economically acceptable.

The static expansion system as a new medium vacuum primary standard in KRISS

A new medium vacuum primary standard using the static expansion method was developed in Korea Research Institute of Standards and Technology. We compared the system with an ultrasonic interferometer manometer using two capacitance diaphragm gauges with full-scale ranges of 133 Pa and 1333 Pa. The results showed that the two standards are coincident with each other within the range of uncertainty at calibrated pressures 3 Pa to 100 Pa.

Simulation of the operation and characteristics of static expansion pressure standards

A flexible, detailed and realistic model for static expansion systems is described. The model is based on the solution of a system of equations relating the pressure in a system of connected vessels at arbitrary temperatures. By simulating the distribution of gas in the system, various processes and procedures associated with static expansion systems have been simulated and validation of the associated, simplified measurement equations has been described. The results reveal a number of features that would otherwise only be accessible in qualitative terms.

Final report on key comparison CCM.P-K4 of absolutepressure standards from 1 Pa to 1000 Pa

A key comparison of low absolute pressure standards, organized under the auspices of theConsultative Committee for Mass and Related Quantities (CCM), was carried out at seven national metrologyinstitutes (NMIs) between March 1998 and September 1999 in order to determine the degrees of equivalence of the standards at pressures in the range 1 Pa to 1000 Pa. The primary standards, which represent two principal measurement methods, included five liquid-column manometers and four static expansion systems. The transfer standard package consisted of four high-precision pressure transducers: two capacitance diaphragm gauges to provide high resolution at low pressures, and two resonant silicon gauges to provide the required calibration stability. Two nominally identical transfer packages were used to reduce the time required for the measurements, with Package A being circulated among laboratories in the European region (Istituto di Metrologia G. Colonnetti, Italy; National Physical Laboratory, UK; Physikalisch-Technische Bundesanstalt, Germany) and Package B in the Asia-Pacific region (CSIRO-National Measurement Laboratory, Australia; Korea Research Institute of Standards and Science; National Physical Laboratory of India). The results obtained were normalized using data obtained from simultaneous calibrations of the two packages at the pilot laboratory (National Institute of Standards and Technology, USA). The degrees of equivalence of the measurement standards were determined in two ways: deviations from key comparison reference values and pairwise differences between these deviations. Apart from results from one NMI that were identified as outliers, the absolute-pressure standards of the participants were generally found to be equivalent and the results revealed no significant relative bias between the two principal methods tested.

隔膜真空計における熱遷移現象の数値解析

The Capacitance diaphragm gauge (CDG) is one of the most important vacuum gauges in low and middle vacuum ranges. The difference of temperature between the sensor head and the vacuum chamber gives a non-linear sensitivity of the gauge depending on the pressure due to thermal transpiration effect. Change in the sensitivity of about 4% between molecular flow regime and viscous flow regime is significant for metrological use of the gauge. In this study, by using a DSMC method, pressure distribution in the connecting tube of the gauge was obtained under the pressure range from molecular flow regime to viscous flow regime with taking account of temperature distribution along the connecting tube. It was in good agreement with the pressure dependence of sensitivity obtained by static expansion system experimentally. Furthermore, influence of gas-surface interaction on the thermal transpiration was also discussed.

A discussion of methods for the estimation of volumetric ratios determined by multiple expansions

The volumetric ratios form a critical component in the characterisation of static expansion systems and periodic re-determination of the ratios is required. In order to avoid disassembly of the system an in-situ procedure is used. Simple explicit equations for the volumetric ratio may only be derived under isothermal conditions, a situation not often encountered under experimental conditions. Methods to account for the temperature gradient between the vessels and the drift in the vessel temperature during the experiment have been developed and are presented.

Volume ratio determination in static expansion systems by means of a spinning rotor gauge

Static or volume expansion systems are used to generate accurately known pressures in the high and medium vacuum range for vacuum gauge calibrations. To determine the volume ratios in such systems, different methods can be used. We have tested the method of using a spinning rotor gauge for measuring pressures before and after an expansion for several gases and compared it with two other independent methods. The results of the volume ratios obtained with the spinning rotor gauge method were in agreement (relative differences ≤3×10 -4) with the results obtained with either of the two other methods.

真空標準の国際比較の実験

Intercomparison of vacuum standards was carried out by using a spinning rotor gauge as a transfer gauge. The accommodation coefficient of the rotor was measured by the static expansion system at the Electrotechnical Laboratory and by the dynamic expansion system at the laboratorys Italian counterpart. The difference between coefficients measured in these two laboratories was 0.7%, which was smaller than the uncertainties of gauge calibration systems.

Intercomparison of vacuum standards between the Physikalisch Technische Bundesanstalt (Germany) and the National Physical Laboratory (India) using two spinning rotor gauges

The paper describes the results of a comparison of low‐pressure standards maintained at the National Physical Laboratory (NPL, India) and the Physikalisch Technische Bundesanstalt (PTB, FRG) over the range 10−3–2 Pa. The intercomparison was carried out by employing spinning rotor gauges shipped with a novel transport device. Both the laboratories, i.e., NPL and PTB, use static expansion systems for pressure generation. The gauge coefficients σ0,eff of the two gauges for Ar agree within ±0.5% for the two laboratories. This result proves agreement of the respective national standards in the above range of pressures. The small deviation of −0.4% between calibrations over a period of one year before and after air‐parcel transportation from Berlin to New Delhi and back is indicative of a careful handling of the rotors during operation and a good performance of the employed transport device.