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PTB-Mitteilungen 3/2011


Karl Jousten

Die PTB richtete vom 1. bis zum 5. Mai 2011 die “5. CCM International Conference on Pressure and Vacuum Metrology“ aus. Es ist die weltweit maßgebende Konferenz auf dem Gebiet der Druck- und Vakuummetrologie und wird alle 6 Jahre von den Arbeitsgruppen für Druck und Vakuum im CCM (Comité consultatif pour la masse et grandeurs apparentées) des CIPM organisiert.
Sie wurde 2011 verbunden mit der 4. Konferenz des Technischen Komitees 16 „Druck und Vakuum“ der IMEKO.

Dieser Band veröffentlicht überwiegend die auf der Konferenz vorgestellten Beiträge, die eine enge Verbindung zu Primärnormalen haben.
Die übrigen Beiträge werden in der Zeitschrift «Measurement» erscheinen.

Historical perspectives of high pressure metrology using pressure balances

Gianfranco Molinar Min Beciet

Development of pressure balances dates back to the beginning of the nineteenth century and was stimulated by the growth of industrial applications of steam engines and by the need of measuring accurately thermodynamic properties of gases and liquids at different pressures and temperatures. An historical review illustrating the fundamental steps in the development of pressure balances in gas and liquid media up to a maximum pressure close to 1 GPa is given.

Pressure measurements in gas media up to 7.5 MPa for the Boltzmann constant redetermination

W. Sabuga

For the redetermination of the Boltzmann constant using a dielectric-constant gas thermometer (DCGT), which requires absolute pressure measurements in helium up to about 7 MPa with a relative standard uncertainty (u) as low as 1 · 10–6, new special absolute pressure balances were developed and characterised. Traceability of pressure measurements up to 7.5 MPa to the SI base units on a low uncertainty level is achieved by improvements in the determination of the piston-cylinder units’ (PCUs) effective area (A0) from dimensional measurements, quality of weights, knowledge of the local gravity acceleration and the cross-float performance of the pressure
balances. With enhanced dimensional measurements and advanced models, A0 of primary 20 cm2 PCUs was determined with u ≤ 0.7 · 10–6. Pressures up to 7.5 MPa are measurable with three 2 cm2 PCUs traceable to the three 20 cm2 PCUs. Pressure distortion coefficients were determined by the finite element method using PCUs’ dimensional and elastic constants, the latter measured by resonant ultrasound spectroscopy. Cross-float measurements were performed in absolute mode using differential pressure cells with υ ≤ 1 · 10–6. The present combined uncertainty of pressures (1–7) MPa is (1.8–2.1)·10–6.
Keywords: Gas pressure balance, effective area, pressure distortion coefficient, finite element analysis, Boltzmann constant

Design and Evaluation of Pressure Balances with 1 ∙ 10–6 Uncertainty for the Boltzmann Constant Project

Wladimir Sabuga, Tasanee Priruenrom, Rob Haines, Michael Bair

In support of the project for determination of the Boltzmann constant by dielectric constant gas thermometry, a system of pressure balances has been designed and constructed with the goal of defining pressures in helium in gauge and absolute measurement modes up to 7 MPa with a relative standard uncertainty of 1∙106. The design addresses temperature stability, mass uncertainty, effective area and pressure distortion coefficient in particular. The system includes two pressure balance platforms, three 20 cm2 and three 2 cm2 piston-cylinder assemblies (PCAs), two 150 kg mass sets and automated mass handlers. The design of the PCAs was optimized to reduce pressure distortion coefficients and mounting induced deformations. In order to perform automated cross-floats with the pressure balances in gauge or absolute mode differential pressure cells (DPCs) were applied to indicate pressure equilibrium. The effective area ratios obtained from cross-floats for all possible combinations of PCAs are consistent within 0.96∙10–6. Using dimensional measurements, the effective areas of the 20 cm2 and 2 cm2 PCAs were determined with relative standard uncertainties of 0.7∙10–6 and 1∙10–6, respectively. Based on the currently available  dimensional and cross-float data the relative standard uncertainty of the absolute pressure of 7 MPa is equal to 2.1∙10–6.

Pressure balance, Boltzmann constant, 1 ppm, cross-float, effective area, pistoncylinder assembly

Determination of the Effective Area of Piston- Cylinder Assemblies Using a Rarefied Gas Flow Model

W. Sabuga, F. Sharipov, T. Priruenrom

Numerical solutions of gas flows between parallel plates and in an annular gap based on the kinetic equation and valid over a wide range of the gas rarefaction are applied to calculate the pressure distribution in the gap between a piston and cylinder, the viscous force acting on the piston and, finally, the effective area of real 10 cm2 and 20 cm2 piston-cylinder assemblies (PCAs) which were accurately  characterised by dimensional measurements and are used as primary gas pressure standards at PTB. The calculations are performed for the gauge and absolute mode as well as for different gases. The calculated effective areas are compared with those obtained by the Dadson theory and with the effective areas’ ratios determined experimentally by the cross float method using nitrogen, helium and sulphur hexafluoride. The results confirm that even in the case of PCAs of a large effective area (≥10 cm2), the effect of the flow regime and of the gas type should be taken into account, if a relative uncertainty in pressure measurements of the order of 10-6 is envisaged and, in particular, when the pressure balances are operated in absolute mode.

Effective area, piston-cylinder assembly, Knudsen number, Poiseuille coefficient, rarefaction parameter

New MSL twin pressure balance facility

Mark Fitzgerald, Chris Sutton, Darrin Jack

This paper describes the design and performance of the new MSL twin gas pressure balance facility which will be used for gauge, absolute and differential gas pressure standards from 1 Pa up to 11 MPa. This new instrument uses large-area piston-cylinder units and replaces the first MSL facility that was developed in the 1980’s to generate small differential pressures. Two key features of the new design are the high thermal conductivity base to minimise temperature differences between the two piston-cylinder units and increased pumping speed and flow conductance to evacuate the region above each piston-cylinder. The new twin pressure balance facility is currently being commissioned and initial results obtained from the instrument are presented including the temperature stability, base vacuum and the performance achieved when generating low differential pressures.

Calculation of Effective Area for the NIM Primary Pressure Standards

Yuanchao Yang, Jin Yue

The primary pressure standards of the National Institute of Metrology (NIM) are a group of five oil-operated piston-cylinder assemblies of 1 cm2 nominal cross-sectional area for the 10 MPa range. The five piston-cylinder assemblies were accurately dimensioned by the length division of NIM, including straightness, roundness and diameter measurements. Based on the dimensional data, the effective areas were calculated with relative standard uncertainties ranged from 5.7 · 10–6 to 11 · 10–6 using the Dadson’s theory. We also carried out the crossfloat measurements between each two of the piston-cylinder assemblies, and the effective area ratios were determined with relative standard uncertainties of about 9 · 10–6. Finally, the effective areas of the five piston-cylinder assemblies were determined taking into account the results of both dimensional characterization and cross-float experiments using generalized least-squares method.

primary pressure standard; piston-cylinder assembly; pressure balance; crossfloat experiment; effective area

New Model Of Fluid Flow To Determine Pressure Balance Characteristics

P. Wongthep, T. Rabault, C. Sarraf and R. Noguera

Some projects like the Euramet Project 463 have underlined the lack of agreement between experimental measurements and calculations by finite element methods (FEM), used to determine the piston fall rate of high-pressure balance used in primary standards. Yet, piston fall rate is an essential parameter to characterize experimentally the mean gap between the piston and the cylinder and to determine the effective area (Ap) at each pressure (p) point. Adjusting the methods to estimate this parameter will improve the characterization of the gap, the determination of Ap and consequently the pressure distortion coefficient. One of the first possible explanations of the significant difference observed between the calculated and measured piston fall rates could be due to the determination of the fluid flow. Indeed, the former quasi 1D Stokes model assimilates the gap between piston and cylinder as formed by two parallel walls, which is an approximation. In addition, the velocity of the piston wall was neglected. In order to evaluate the influence of this model, the equations of the fluid flow are modified and are presented in this paper. Equations that were defined in a parallel planes model are defined in an annular gap model. Besides this, corrections due to the velocity of the piston wall are inserted. This research work is applied on a Desgranges et Huot DH 7594 piston-cylinder unit of PTB with a pressure up to 1 GPa, in the continuity of EURAMET Project 463 in order to quantify the influence of each correction that has been inserted in the new equations. This is carried out by using FEM. This evaluation will allow us to evaluate the improvement of our knowledge on the behavior of piston gauges and consequently to better evaluate the uncertainties due to the models.

Multiple cross-float system for calibrating pressure balances

Tokihiko Kobata

Multiple cross-float system for calibrating pressure balances has been developed. The system mainly consists of multiple pressure balances, multiple air-operated constant volume valves, a pressure controller and a precise pressure transducer. For comparing the pressures generated by the pressure balances accurately, the differential pressures between them are measured by using a comparator method. In the system, one pressure balance can be used as a reference and other test pressure balances are compared with the reference one after another by switching the valves. From the differential pressures obtained, the pressure generated by each test pressure balance is calibrated. The system can calibrate the unknown pressures generated by multiple pressure balances nearly simultaneously. In this article, the system configuration and the measuring principle are described. The typical measurement result using the system is also shown.

Stability of pressure generated by controlledclearance pressure balance up to 1 GPa

Hiroaki Kajikawa, Kazunori Ide, Tokihiko Kobata

The large pressure balance equipped with a controlled-clearance piston-cylinder (CCPC) and weights of totally 1100 kg has been developed in NMIJ with the aim of improving the hydraulic pressure standard up to 1 GPa. Among several CCPCs, a newly-developed 1 MPa/kg CCPC is evaluated in terms of the stability of generated pressure and the piston fall-rate at pressures up to 1 GPa. The stability of generated pressure is similar to or better than that by top-level commercial pressure balances. The piston fall-rate is less than 0.15 mm/min under the ordinary crossfloating condition. It is confirmed that the 1 MPa/kg CCPC can generate the pressure stably during characterization experiments and calibrations.

Linking Hydraulic and Pneumatic Pressure Scales Using a Common Piston Gauge

Neville Owen

NMI Australia realises a pneumatic pressure scale using a mercury manometer and a hydraulic pressure scale using a 490 mm² piston gauge (DHI01). To compare these two scales we have a very low clearance 100 mm² stainless steel piston gauge (R123) which can be operated using Di‑2‑Ethylhexyl Sebacate (DHS) or nitrogen as the pressure transmitting fluid. To allow effective cross floating between piston gauges with large fall rate differences required improved fall rate systems which will be briefly discussed. The cross floats conducted have provided valuable information when implementing DHI01 as a primary standard by confirming correct accounting for all forces on the piston gauge and have allow linking these two pressure scales with greater confidence. This work has also provided a much better estimate of the real distortion coefficient operating on the pneumatic range piston gauges.

pressure scale; calibration; crossfloat method

Traceability of the pressure balance effective area at MIKES

Sari Saxholm, Björn Hemming, Martti Heinonen, Pierre Otal, Markku Rantanen, Veli-Pekka Esala, Antti Lassila

Centre for Metrology and Accreditation (MIKES) is using pressure balances as national measurement standards for pressure. Pressure balances are used in ranges 0 to 500 MPa gauge pressure and 20 Pa to 1,8 MPa absolute pressure. MIKES has now started to determine effective areas by itself and aims to be a primary pressure laboratory.

Two of the piston cylinder units are selected to be the reference standards, one with a diameter 35 mm and the other with a diameter 50 mm. The effective area for the piston cylinder unit no. 6687 (35 mm) is determined from dimensional measurements made by MIKES and from crossfloating results made by LNE. The effective area for the piston cylinder unit no. 451 (50 mm) is determined from dimensional measurements made by MIKES and LNE and complemented with cross-floating made by LNE.

The effective areas for working standards are derived from the two dimensionally characterised piston cylinder units. There are totally 13 piston cylinder units as working standards. The cross-floating method [1] is performed for the units which overlap. The effective areas for higher pressures are calculated with help of the pressure distortion coefficients. One of the reference standards and four of the working standards has been traceable to LNE for almost 20 years. The data from this gives a strong support to the  implementation of the in-house traceability and the new traceability chain of MIKES pressures.

Traceability of NIS Piston-Cylinder Assemblies up to 500 MPa

Alaaeldin A. Eltawil, Shaker A. Gelany, Ali H. Magrabi

Measurement made using single equipment with one-to-one correspondence, without any functional relationship, is called direct measurement. This is not the case with pressure measurements where the parameter under test is functionally related to other parameters  and has to be indirectly evaluated. Traceability of pressure measurements up to 1 MPa using pneumatic gauge pressure with relative  uncertainty of few ppm was established from dimensional measurements of the piston cylinder assembly (PCA) in conjunction with mass  measurements and adequate measurements for the acceleration of gravity.

Using a set of cross floating experiments the traceability was transferred to the pneumatic pressure up to 40 MPa and hydraulic pressure measurements up to 500 MPa in NIS pressure lab. Such traceability was validated by participating in several key comparisons with all accepted measurements within the claimed uncertainty and set of measurements using PCA that was calibrated by other recognized NMI.

EURAMET Key Comparison for 500 MPa Range of Hydraulic Gauge Pressure (EURAMET.M.P-K13)

I. Kocas, W. Sabuga, M. Bergoglio, A. E. Eltawil, C. Korasie, P. Farar, J. Setina, B. Waller

The regional key comparison
EURAMET.M.P-K13 for pressure measurements in liquid media from 50 MPa to 500 MPa was piloted by the TÜBİTAK UME Pressure Group Laboratories, Turkey. The transfer standard was a DH-Budenberg pressure balance with a free deformation piston-cylinder unit of 2 mm2 nominal effective area. Seven laboratories from the EURAMET region, namely PTB, INRIM, NIS, SMU, IMT and NPL, and one laboratory from the APMP region, NMISA, participated in this comparison. PTB participated in this comparison as a link between this comparison, previous 500 MPa comparison EUROMET 881 and 500 MPa CCM key comparison CCM.P-K13. All participants’ results with exception of only one value at 500 MPa at were found to be consistent with each other and with the calculated reference value, within their claimed uncertainties, at all pressures. The results are therefore considered to be satisfactory.

Evaluation of cross-float measurements with pressure balances – Results of EURAMET project 1125

P. Otal, I. Morgado1, D. Steindl, N. Medina Martín, A. Lefkopoulos, A. Altintas, L. Grgec Bermanec, S. Bursic, J. Setina, M. Bergoglio, I. Spohr, C. Wüthrich, M. Rantanen, C. Vámossy, W. Sabuga, I. Koçaş

Fifteen European metrological institutes have compared their approaches to estimate the effective area parameters resulting from the calibration of pressure balances by cross-floating. The methods in estimating these parameters and the associated uncertainties are tested by applying four calibration data sets simulated numerically, two in gas (up to 10 MPa) and two in oil (up to 500 MPa). The performance of the methods is evaluated in terms of robustness and ability to estimate the uncertainties of the effective area parameters.

Keywords: pressure balance, effective area, cross-float, pressure distortion coefficient

Comparison between GUM and Monte Carlo uncertainty frameworks in pressure field

Salustiano Ruiz, Nieves Medina

A comparison between the results of an uncertainties assessment, using different approaches, of the calibration of pressure standards (mercury column, piston cylinder assemblies and static expansion system) is made. First a classical GUM analysis is performed using the Welch-Satterthwaite formula and supposing different degrees of freedom for the uncertainties components estimated by the type B method. These results are compared with the ones obtained by Monte Carlo simulation suggested in the GUM Supplement 1. In all cases the same mathematical model is used and the same assumptions for the different uncertainty components are made. The obtained results demonstrate the equivalence of both methods for all cases except in the characterization of the static expansion system where GUM method reached  different values due to the fact that the mathematical model used is significantly nonlinear.

The laser interferometric oil manometer with floats

Irina Sadkovskaya, Aleksey Eichwald

The uncertainty of laser interferometric oil manometer (LIOM) at pressures lower than 10 Pa is determined mostly by its repeatability. The last one has been researched in the comparison of two LIOMs having similar design. It has been found to be less than the resolution of LIOM that is 1,4 mPa.

The Mercury Micromanometer at PTB

J. Könemann, S. Ehlers, M. Jescheck, W. Sabuga

In this work, we present for the first time the mercury micromanometer experiment at PTB. Our system consists of a classical three-limb U-tube manometer for gauge pressures in the range of (-10 to 10) kPa and absolute pressures in the range between 170 mPa and 10 kPa. The length determination of the mercury columns is performed by plane mirror interferometer systems and heterodyne signal processing. As a result, we are able to demonstrate first measurements of the operation and a preliminary estimation of the combined measurement uncertainty.

Keywords: Low pressure, Interferometers, Units and standards, Mass and density

Static Expansion System Validation at CEM

D. Herranz, N. Medina1, S. Ruiz, J. Torres-Guzmán

The static expansion system of CEM has been validated by a comparison with a force-balanced piston gauge and the static expansion system of CENAM by using a capacitive diaphragm gauge (CDG 133.32 Pa) and a spinning rotor gauge (SRG) as transfer standards. This paper shows the results of this validation.

Characterization of the medium and high vacuum primary standard at CENAM, Mexico

A. Navarro-Nateras, J. C. Torres-Guzman

A static expansion systems (SEE-1) is the primary standard for vacuum at the Centro Nacional de Metrología, this system has four volumes, it’s measurement range is from 10-4 Pa to 103 Pa. This article describe a new characterization of the system, basically the determination of the expansion ratios by two methods: the gas accumulation method and the method with a linearized spinning rotor gauge (SRG).

Characterization of the LNE constant pressure flowmeter for the leak flow rates measurements with reference to vacuum and atmospheric pressure

Frédéric Boineau

The Laboratoire national de métrologie et d’essais (LNE) developed a constant pressure gas flowmeter to implement the continuous expansion standard. The characterization of this new standard and the associated uncertainty budget are presented in this paper.  Comparisons were carried out between the constant pressure flowmeter and our other flowmeters for leak rates flowing in vacuum (constant volume flowmeter) and atmospheric pressure (infrared detection flowmeter).

gas flow rates / gas flowmeter / leak detection

International standardization for vacuum metrology and technology in recent years

K. Jousten

International standardization for vacuum metrology and technology has in recent years focused on laying down the basics for pressure dissemination in the vacuum range and on the characterization of vacuum pumps. Other issues were the safety of turbomolecular pumps and compatibility of vacuum hardware. Traceability to the SI and the evaluation of measurement uncertainties play an important role in the standardization for vacuum instrumentation.

Keywords: Vacuum metrology, standardization, ISO, vacuum technology

Traceability and accreditation process for vacuum and pressure laboratories in AFRIMETS

C. Korasie, A. Eltawil

This paper will look at the process, developing NMI’s in Africa go through to establish an NMI from mostly Trade and or Legal Metrology requirements. The aim is to investigate the challenges countries are faced with in obtaining traceability and eventually accreditation. A case study will be made of the roadmap followed by NMI’s that has successfully entered CMC’s in the BIPM database. With limited resources the tools required to maintain these newly formed NMI’s and how to increase capability in various parameters will be scrutinized.

Keywords: accreditation, traceability, capability