Static Expansion System Research Articles

Low-pressure performance of a Fabry–Pérot cavity based optical pressure standard working at the zero-thermal-expansion temperature

Fabry–Pérot cavity (FPC) refractometer based optical pressure standard (OPS) is very promising for a new realization of the pascal in the range 1 Pa–100 kPa. Although FPCs are made using ultra-low-expansion glass, cavity baseline (frequency) shifts due to temperature changes caused by gas pumping and filling are still a crucial factor limiting the accuracy of the OPS developed at the National Institute of Metrology (NIM) of China at the low-pressure end. In this study, the baseline shift in the NIM-OPS is eliminated by setting the working temperature at the zero-thermal-expansion (ZTE) point, which is determined by measuring the coefficient of thermal expansion (CTE) of the FPC in the temperature range 23–40 °C. CTE measurements are obtained under a background vacuum, and also under the condition of remaining gas in order to minimize the temperature gradient. The performance of the OPS for low-pressure measurements is investigated at two different working temperatures, i.e. 30.1 °C used previously and the determined ZTE temperature of 36.8 °C. An indirect comparison between the OPS and a static expansion system is performed at 1 Pa using a capacitance diaphragm gauge as the transfer standard. The disagreement of ∼ 254 mPa at 30.1 °C is reduced to within 10 mPa at the ZTE temperature.

Analysis of the mathematical modelling of a static expansion system

Static expansion systems are used to generate pressures in medium and high vacuum and are used in the calibration of absolute pressure meters in these pressure ranges. In the present study, the suitability of different models to represent the final pressures in a static expansion system with two tanks is analysed. It is concluded that the use of the ideal gas model is adequate in most simulated conditions, while the assumption that the residual pressure is zero before expansion presents problems under certain conditions. An uncertainty analysis of the process is carried out, which leads to evidence of the high importance of uncertainty in a first expansion over subsequent expansion processes. Finally, an analysis of the expansion system based on uncertainty is carried out to estimate the effect of the metrological characteristics of the measurements of the input quantities. Said design process can make it possible to determine a set of restrictions on the uncertainties of the input quantities.

Validation of a PTB force-balanced piston gauge primary pressure standard

Experimental methods using different pressure standards were applied to verify theoretical results obtained for the effective area of the piston-cylinder assembly (PCA) and for pressures measured with a force-balanced piston gauge (FPG). The theoretical effective area was based on the PCA’s dimensional properties defined via diameter, straightness and roundness measurements of the piston and cylinder, derived by gas-flow modelling using principles of the rarefied gas dynamics, and presented as two values: one obtained for absolute and the other for gauge pressure operation mode. Both values have a relative standard uncertainty of 5×10<sup>-6</sup>. The experimental methods chosen were designed to cover the entire operating pressure range of the FPG from 3 Pa to 15 kPa. Comparisons of the FPG with three different PTB pressure standards operated in different pressure ranges – a pressure balance, a mercury manometer and a static expansion system – were performed using the cross-float method and by a direct comparison of the generated pressures. For the theoretical and experimental effective area, as well as for pressures generated by the FPG and the reference standards, all the results demonstrated full agreement within the expanded uncertainties of the standards.

Uncertainty evaluation of the static expansion system and its long-term stability at NMIJ

A pressure standard based on the static expansion of gases has been made available at the National Metrology Institute of Japan (NMIJ) for gauge calibrations in the range of 0.1 mPa–2 kPa over the past 30 years. The static expansion system (SES) generates calibration pressures by multiple-step gas expansions using two expansion ratios (R900≃907.3 and R50≃53.4). These expansion ratios were determined using the two reference gauges method instead of the one reference gauge method, which has been in use thus far. Relative uncertainties of 0.073% (k = 1) for R900 and 0.036% (k = 1) for R50 were obtained, and the calibration uncertainties were slightly improved compared to the current calibration and measurement capability (CMC) of the SES at NMIJ as follows:U = 0.28% (k = 2) (1 mPa–10 Pa) for spinning rotor gauges (SRGs).U = 0.23% (k = 2) (0.2 Pa–10 Pa) for capacitance diaphragm gauges (CDGs).U = 0.17% (k = 2) (10 Pa–110 Pa) for CDGs.In addition, the calibration results of the check standards of the past 12 years are reported. The data suggest that the SES was stable compared to the calibration uncertainty over the years.

Characterization of spinning rotor gauge-3 using orific flow system and static expansion system

This article elucidates the calibration of newly procured spinning rotor gauge (SRG 3) from MKS Instruments, USA using primary vacuum standards: Orifice flow system (OFS) and Static expansion system (SES) established at National Physical Laboratory, India (NPLI) in the range of 10<sup>-4</sup> Pa to 1 Pa and further compared with manufacturer reported value which was calibrated by transfer standard of National Institute of Standards & Technology (NIST). The key parameters to calculate the pressure measured by SRG is the accommodation coefficients. The accommodation coefficients for N<sub>2</sub> gas obtained using OFS, SES, and calibration report form NIST USA (SRG2) are 0.957, 0.961, and 0.954 respectively.

Investigation of the effects of valve closing in a static expansion system

The precise measurement of the pressure of the gas enclosed in the starting volume of a static expansion system is important for achieving low measurement uncertainties. This work focuses on the valve closing process and the resulting pressure difference. The condition of flow conservation is used to set up a model and an experimental procedure has been developed to investigate the pressure change caused by the moving valve plate. Various parameters are evaluated and compared with experimental data.

Remarks concerning about the characteristics of the extractor vacuum gauge and the Quadrupole Mass Spectrometer

In this study, the stability of an extractor gauge (EXG) was investigated through the determination of correction factors (CFs) over a pressure range 5 × 10−5 Pa to 9 × 10−3 Pa by using a Spinning Rotor Gauge (SRG) traceable to UME Static Expansion System, during 20 months and 15 months for N2 and He, respectively. Percent and fractional changes in CFs were studied and sensitivities of EXG were also presented for Ar and CO2. Direct comparison method was used for EXG stability measurements. Additionally, sensitivity measurements of Quadrupole Mass Spectrometer (QMS) were performed in the range of 1.0 × 10−6 Pa to 1.0 × 10−2 Pa at emission currents of 2 mA, 0.4 mA and 0.1 mA for He, N2 and Ar. Long-term stabilities of QMS for N2 and He were analyzed for about 2 years. EXG and SRG were used for QMS sensitivity measurements.The changes in CF of EXG remained within ±5% and ±6%, and fractional changes remained within about ±0.03 and ±0.05 for seven and five different measurement runs for N2 and He, respectively. The change in CF of EXG based on the mean value of the relevant pressure point is 5.8% and 7.8% at 5 × 10−5 Pa, 5.3% and 5.9% at 9 × 10−3 Pa, and maximum CF changes relative to the first calibrations ranges from −1.7% to 2.4% and from −1.0% to 4.7% within the selected pressure range for N2 and He, respectively. The changes of QMS sensitivity are strongly dependent to the electron current. Maximum changes of QMS sensitivities over a three month period are 44% and −35% for N2 and He, respectively. This study was conducted in the frame of EMRP IND12 “Vacuum Metrology for Production Environments” project that was funded by the European Metrology Research Programme (EMRP).

TÜBİTAK UME vacuum laboratory capabilities and activities

TÜBİTAK National Metrology Institute (TÜBİTAK UME) is a research and development institute that operates under the Scientific and Technological Research Council of Turkey (TÜBİTAK). TÜBİTAK UME Vacuum laboratory takes part in under the mechanics group among the groups of physics, mechanics and chemistry group laboratories. TUBITAK UME Vacuum Laboratory aims to develop and maintain national measurement standards, to establish vacuum pressure traceability to SI units and to disseminate this to industry, science and research in Turkey. The laboratory was founded in 1996 and started to provide secondary level calibration services with Vacuum Gauge Calibration System (VGCS-200). Primary vacuum standard called Multi-Stage Static Expansion System (MSSE1) was established in 2000. Commercially available secondary vacuum gauge calibration system was improved with the addition of automation under the name Vacuum Gauge Metrology System (VGMS) in 2010. The main activities of the Vacuum Laboratory are conducted in the following working fields: Primary and secondary vacuum measurements and calibrations, secondary calibrations of leak standards, primary constant pressure flowmeter (CPFM) standard establishment works, renewal works of existing primary static expansion system, European Metrology Research and Innovation Projects, Quadrupole Mass Spectrometer (QMS) characterization measurements on Dynamic Vacuum System (DVS), training and consultancy services in the field of vacuum metrology. In this paper, the Vacuum Laboratory capabilities and activities will be briefly introduced.

Final report on the key comparison, CCM.M.P-K15.1 in the pressure range from 1.0 × 10-4 Pa to 1.0 Pa

At the CCM WG-LP meeting in Berlin in April 2011 the National Institute of Metrology of the people's republic of China asked for an opportunity to be linked to the CCM.M.P-K15 comparison which just ended. METAS, which had been active as pilot for the CCM.M.P-K15, agreed to make a link with NIM. The NIM introduced a new static expansion system in his laboratory.Two spinning rotor gauges and a control electronic are used as transfer standard. The circulation of the transfer standard was made in spring 2012. The drift of the accommodation coefficient of the two SRG was measured by the pilot before and after the comparison. The stability of the transfer standards was excellent and the equivalence between METAS and NIM has been demonstrated.A link to the CCM.M.P­K15 has been established using the results from METAS. It has been possible to achieve a link with a small uncertainty due to the strong correlation of the measurements of METAS in the two comparisons.Main textTo reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Calibration of Capacitance Diaphragm Gauges with 1333 Pa full scale by Direct Comparison to Resonant Silicon Gauge and Static Expansion System

<p>Two capacitance diaphragm gauges (CDGs) with 1333 Pa full scale, with a heated sensor head and an unheated one, respectively, were calibrated by three different methods; direct comparison to a resonant silicon gauge calibrated by a pressure balance, direct comparison to a CDG with 133 Pa full scale calibrated by a static expansion method, and the static expansion method. The calibration results of the three calibration methods show good agreement within their claimed uncertainties. Calibrated higher pressure points of CDGs by the pressure balance and lower pressure ones by the static expansion system are linearly interpolated within the calibrated uncertainty. Here, compensation of the thermal transpiration effect is important when a CDG is used with a heated sensor head.</p>

Measurement Uncertainties for Vacuum Standards from a Low to an Ultra-high Vacuum

The Korea Research Institute of Standards and Science (KRISS) has three major vacuum systems: an ultrasonic interferometer manometer (UIM; Section II, Figs. 1 and 2) for a low vacuum, a static expansion system (SES; Section III, Figs. 3 and 4) for a medium vacuum, and an orifice-type dynamic expansion system (DES, Section IV, Figs. 5 and 6) for high and ultra-high vacuum systems. For each system, explicit measurement model equations with multiple variables are given. According to ISO standards, all of these system variable errors were used to calculate the expanded uncertainty (U). For each system, the expanded uncertainties (k = 1, confidence level = 95%) and relative expanded uncertainty (expanded uncertainty/generated pressure) levels are summarized in Table 4. Within the uncertainty limits, our bilateral and key comparisons [CCM.P-K4 (10 Pa to 1 kPa)] are extensive and in good agreement with those of other nations (Fig. 8 and Table 5).

Measuring volume ratios of vacuum vessels using non-evaporable getters

Several methods have been used in vacuum metrology for volume determination. Volume ratios can be determined by different gas expansion methods, which were primarily developed for the precise determination of expansion ratios in static expansion systems. Measurements of the volume ratios using the gas expansion methods below 10−2 Pa are influenced by outgassing from chamber walls. To reduce outgassing in the expansion chambers during measurements at low pressures, we have installed non-evaporable getter (NEG) pumps, which pump hydrogen and other active gases but have a negligible pumping speed for inert gases. The volume ratio of two chambers of an experimental static expansion system has thus been measured using the inert gases argon, helium and krypton. The obtained results were compared with the measurements without the use of an NEG pump. Measurements of the pressure ratios were performed with a spinning rotor gauge (SRG).

The Improvement of the Volume Ratio Measurement Method in Static Expansion Vacuum System

Abstract Expansion ratio or volume ratio is the most important parameter in the static expansion system. To determine the volume ratios in such systems, different methods can be used. We have improved the methods with the reference volume method, the sequential increment method and the pre-pressurization accumulation method. The deviations of there results are about 10 -4 .

The characterization of new VGMS (vacuum gauge metrology system) by the traceability of multi stage static expansion system

In this study, the design and characterization of vacuum gauge calibration system which was upgraded is described. A capacitance diaphragm manometer is used to characterize the system performance. 1Torr and 10Torr CDGs are available to compare the performance of VGMS system which is traceable to the static expansion system generating calibration pressures in the range of 9×10−4Pa up to 1×103Pa. The working pressure range of VGMS system is 1×10−4–1.3×105Pa. It is used a comparison method as a calibration process. After making the system description and process, the results of calibrations included uncertainty values are given to determine long term instability and show the performance of the system.

진공측정표준의 불확도 평가모델 개발

한국표준과학연구원(Korea Research Institute of Standards and Science, KRISS)에는 초음파간섭 수은주압력계(ultrasonic interferometer manometer, UIM), 정적형표준기(static volume expansion system, SVES), 오리피스형 정압표준기(orifice-type dynamic expansion system, ODES) 등 세 개의 주요한 국가 진공표준기가 있다. 이 장치들의 불확도 평가를 위해 각각 변수들의 측정 및 계산 모델을 개발하였다. 국제표준화기구(International Organization for Standardization, ISO) 지침에 따라 표준기들의 확장불확도(expanded uncertainty, U)를 계산하였다. The Korea Research Institute of Standards and Science (KRISS) has three major vacuum systems: an ultrasonic interferometer manometer (UIM), a static volume expansion system (SVES), and an orifice-type dynamic expansion system (ODES). For each system explict measurement model equations with multiple variables are respectively given. According to ISO standards, all these system variables errors were used to calculate the expanded uncertainty (U).

Development of vacuum metrology in National Institute of Metrology

Overview of the vacuum metrology development at the National Institute of Metrology, China is presented, including the different vacuum standards established years ago, the recently developed static expansion system and its characterization and the new compensated micro-manometer. Recent research of the performance of capacitance diaphragm gauges (CDGs) in Knudsen flow region, as well as the ongoing project on the constant pressure flow meter, micro-conductance measurement are also outlined.

中真空標準場装置（膨脹法装置）の安定性

中真空標準場装置（膨脹法装置）の安定性

Compensation of Thermal Transpiration Effect for Pressure Measurements by Capacitance Diaphragm Gauge

The thermal transpiration effect shown in intermediate flow and molecular flow regions influences the sensitivity of a capacitance diaphragm gauge (CDG) with a temperature controlled sensor head. This apparent change in the sensitivity of CDG owing to the thermal transpiration effect has to be compensated for precise pressure measurements in the range of lower than 150 Pa. In this study, the method and the uncertainty of the compensation are reported. Seven types of equations for the thermal transpiration effect were compared with the calibration results of high accuracy CDGs by the static expansion system. Takaishi-Sensui equation, Miller equation, and Setina equation show good agreement with the calibration results. The calibration results of CDGs also show that increasing the temperature of the vacuum chamber from 22.5°C to 26.0°C caused decreasing the sensitivity of CDGs by the thermal transpiration effect. The magnitude of the decrease in the sensitivity was from 0.09% for 10 Pa to 0.5% for 0.1 Pa. Such apparent changes in the sensitivity owing to the thermal transpiration effect could be compensated within 0.2% by Takaishi-Sensui equation using parameters quoted from the catalog and the literature values. In addition, this deviation could be reduced to less than 0.1% by fitting Takaishi-Sensui equation using the parameter c or the sensor temperature T2.

Static expansion primary vacuum standard — Part 1: Determination of the volume ratio of the expansion stage

Measurement of volume ratio forms an essential part of the characterization of a static expansion system (SES) for the generation of pressures in the medium and high vacuum region. Because of the complexity of the vacuum chambers, it is not possible to determine the absolute volumes of the chambers involved. Hence an expansion process is resorted to, in which the gas enclosed in the small volume at a known pressure is allowed to expand, under isothermal conditions, into the large volume. The accuracy of the volume ratio thus determined depends on the stability of the vacuum gauges used for the measurement of initial and the final pressures and the ambient temperature. High accuracy resonant silicon gauges (RSGs) of two different ranges, one 130 kPa full scale and the other 1 kPa full scale for measurement of the initial and final pressures are found to be useful. This paper reports the results obtained with these RSGs for the measurement of the volume ratio of the National Physical Laboratory, India (NPLI) SES which is nominally 2820. With the use of the RSGs, and calibrated platinum resistance thermometers (PRTs) mounted inside the vacuum chambers, it has been possible to measure the volume ratio within the relative expanded uncertainty (k = 2) of 0.0014. The results of the volume ratio determination exercise are given in this paper while the Part 2 of this paper will discuss the procedure for the calibration of spinning rotor gauges on the Static expansion primary standard.

Measurement uncertainties for vacuum standards at Korea Research Institute of Standards and Science

The Korea Research Institute of Standards and Science has three major vacuum systems: an ultrasonic interferometer manometer (UIM) (Sec. II, Figs. 1 and 2) for low vacuum, a static expansion system (SES) (Sec. III, Figs. 3 and 4) for medium vacuum, and an orifice-type dynamic expansion system (DES) (Sec. IV, Figs. 5 and 6) for high and ultrahigh vacuum. For each system explicit measurement model equations with multiple variables are, respectively, given. According to ISO standards, all these system variable errors were used to calculate the expanded uncertainty (U). For each system the expanded uncertainties (k=1, confidence level=95%) and relative expanded uncertainty (expanded uncertainty/generated pressure) are summarized in Table IV and are estimated to be as follows. For UIM, at 2.5–300Pa generated pressure, the expanded uncertainty is <4.17×10−2Pa and the relative expanded uncertainty is <1.18×10−2; at 1–100kPa generated pressure, the expanded uncertainty is <7.87Pa and the relative expanded uncertainty is <7.84×10−5. For SES, at 3–100Pa generated pressure, the expanded uncertainty is <1.77×10−1Pa and the relative expanded uncertainty is <1.81×10−3. For DES, at 4.6×10−3–1.3×10−2Pa generated pressure, the expanded uncertainty is <1.04×10−4Pa and the relative expanded uncertainty is <8.37×10−3; at 3.0×10−6–9.0×10−4Pa generated pressure, the expanded uncertainty is <8.21×10−6Pa and the relative expanded uncertainty is <1.37×10−2. Within uncertainty limits our bilateral and key comparisons [CCM.P-K4 (10Pa–1kPa)] are extensive and in good agreement with those of other nations (Fig. 8 and Table V).