Pretoria, South Africa
Pretoria, South Africa
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Kruger O.,NMISA | Hungwe F.,NMISA | Farid N.,NIS | Schreve K.,SUN
International Journal of Metrology and Quality Engineering | Year: 2014

At NMISA the SI unit for length is realised by an iodine stabilised He-Ne laser, an optical measurement. In industry most measurements are performed by mechanical probing. Gauge blocks are the link between the optical measurements and the mechanical measurements, and are therefore critical in disseminating traceability. The gauge block length is currently determined by wringing the gauge block onto a platen. This is laborious, requires skill and causes contact errors. Since around 1943, there have been efforts to build a double ended interferometer where gauge block length can be determined without wringing it onto a platen. While there has been a lot of progress in building DEIs, to date, there is still no commercially available DEI. We present a collaboration project between the National Metrology Institute of South Africa (NMISA), the National Institute of Standards (NIS Egypt) and Stellenbosch University (SUN) in South Africa to build a double ended interferometer for use at the respective National Metrology Institutes. We investigate improvements to the interferometric calibration of gauge blocks and recent developments. The different systems currently in use in the national metrology laboratories are described and various designs are investigated. Lastly the expected outcome of the project will be discussed. © 2014 EDP Sciences.

Bailat C.J.,IRA | Keightley J.,NPL | Nedjadi Y.,IRA | Mo L.,Australian Nuclear Science and Technology Organization | And 21 more authors.
Metrologia | Year: 2014

Detailed uncertainty reporting is imperative for proficiency tests and comparison exercises since uncertainties need to be comparable and trusted by all the participants. Even though participants do their best to follow the Guide to the Expression of Uncertainty in Measurement1, ambiguities and divergences about uncertainty evaluation remain. Consequently, to analyze the situation, the CCRI (II) Uncertainties Working Group proposed a comparison exercise (CCRI(II)-S7) about the uncertainty evaluation of a relatively simple primary activity measurement: The standardization of a 60Co source by coincidence counting. To be able to understand how various NMIs calculate coincidence counting uncertainties, our study focused on two of the dominant uncertainty components commonly quoted for 4 αβ-γ coincidence counting in the International Reference System (SIR) submissions and Key Comparison exercises: Efficiency-extrapolation and weighing. Participants from twelve different laboratories were sent the same set of measurement data from the analysis of a 60Co solution standardized at the National Physical Laboratory (NPL). Our study demonstrated the extent of the different interpretations of the uncertainty components. Some factors causing large discrepancies were isolated and are discussed. Further studies of other techniques using a similar approach would be beneficial for the metrology community.

Yu K.M.,Korea Research Institute of Standards and Science | Kim W.S.,Korea Research Institute of Standards and Science | Han K.S.,Korea Research Institute of Standards and Science | Hsu J.C.-M.,CMS | And 11 more authors.
CPEM Digest (Conference on Precision Electromagnetic Measurements) | Year: 2014

A key comparison for the 10 Mo and 1 Go resistance, APMP.EM-K2, has been carried out by the Asia-Pacific Metrology Program(APMP) Regional Metrology Organization(RMO). The purpose is to establish the degree of equivalence of resistance among the national metrology institutes(NMIs) within APMP, in support of CIPM Mutual Recognition Agreement(MRA). The key comparison artifacts are three 10 Mo and three 1 Go resistance standards which was loaned from NIST and the 13 NMIs were participated in the comparison. The results will be presented at the conference. © 2014 IEEE.

Tan S.L.,Industrial Technology Research Institute of Taiwan | Chin J.-H.,Japan National Institute of Advanced Industrial Science and Technology | Takatsuji T.,Japan National Institute of Advanced Industrial Science and Technology | Horita M.,Japan National Institute of Advanced Industrial Science and Technology | And 12 more authors.
Metrologia | Year: 2014

A total of 15 parameters were measured on 5 diameter standards. Calibration is performed by comparison with reference standards. Uncertainty of the calibration by comparison is influenced by the multipurpose length measuring machine, the environment temperature, and the setting and adjustment of the object calibrated, among others. The measurement schedule was planned to last approximately 30 months; however, due to some delays, was actually completed in 32 months. The delay of the diameter standards circulation was partly due to custom operations. Nevertheless, measurement results have been submitted by all NMIs despite some scratches of the diameter measuring sections being reported during circulation. The repeated measurements by the pilot institute showed an acceptable stability except for the 24 mm plug gauge.

Nel M.,NMISA | Theron B.,South African Council for Scientific and Industrial Research
EngineerIT | Year: 2010

Uncertainty contributions when performing a power responsivity calibration for a fiber optic power meter is discussed. The measurement set-up includes a source of the required wavelength of 1310 or 1550 nm and an attenuator serving to reduce back-reflections into the source and to set the power to the desired level. Uncertainty contributions of the standard and UUT associated with the calibration are obtained from a calibration certificate, specifications, or empirical measurements. To empirically quantify the effect of connector tightening, two readings are taken at each measurement, which for briefness are labeled tight and untight. The causes of the connector-tightening effects include when the connector is tighter, is more strain on the connector tip, leading to micro bending and deformation, influencing optical polarization and reflections.

Matthee C.F.,NMISA | Burger J.P.,NMISA | Kritzinger R.,MTN Inc
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2014

A new electrically insensitive optical fibre link was installed between two buildings using commercially available equipment. The aim of the link was to transfer the frequency accuracy from the South African National Measure- ment Standard for Time and Frequency (derived from caesium atomic clocks) to an optical frequency comb. This enables direct traceability of optical frequency measurements to internationally verified time standards (UTC), via the timing links at the National Metrology Institute of South Africa (NMISA). A clean-up oscillator is used to improve any degrading of the stability caused by the laser link. Highly precise loop-back experiments were done to verify the accuracy and stability of the fibre link and clean-up oscillator combination. The nature and results of such experiments are presented here, in order to demonstrate the traceability of the fibre link, and therefore the traceable link between the optical frequency comb and the National Measurement Standards for Time and Frequency of South Africa..

Veldman C.S.,NMISA | Lefenya T.M.,NMISA
XXI IMEKO World Congress "Measurement in Research and Industry" | Year: 2015

The National Metrology Institute of South Africa designed an air bearing linear translation stage (LTS) used for primary low frequency accelerometer calibration. The LTS serves as a replacement of a commercial LTS. The motivation for the new design consideration is touched on. The performances of both LTSs were evaluated in terms of their flatness, straightness, roll, pitch and dynamic transverse motion; the results and findings of which are reported in some detail. The influence of the mechanical connection between the LTS and the electrodynamics exciter was also investigated.

A common measurement model for a gas operated piston-cylinder based pressure standard effective area is the well known integral equation formulation originally developed by Dadson of the NPL. However a problem with directly applying this exact mathematical model is that it cannot be easily cast into a functional form suitable for application of the Guide to the expression of Uncertainty in Measurement (GUM) which is reliant on the concept of sensitivity coefficients without various simplifications. In this paper, we examine the standard approximations that are currently necessary in order to directly apply the GUM for a pressure standard effective area uncertainty determination. We also compare and contrast this to the exact effective area uncertainty results obtained through the direct application of the Monte Carlo Method (MCM) which has recently been published as Supplement 1 to the GUM. Based on these investigations we also draw some preliminary conclusions on the relative merits on the extent to which the shape of the piston and cylinder radii and whose uncertainties may vary along the engagement length of the piston-cylinder may be modeled and incorporated into a piston-cylinder's effective area uncertainty calculation. © EDP Sciences 2010.

Kim D.E.,Pennsylvania State University | Manga V.R.,Pennsylvania State University | Prins S.N.,NMISA | Liu Z.-K.,Pennsylvania State University
Calphad: Computer Coupling of Phase Diagrams and Thermochemistry | Year: 2011

Thermodynamic description of the AlPt binary system is modeled by combining first-principles calculations with the CALPHAD method. The four-sublattice and two-sublattice compound energy formalisms are used to model the ordered L1 2 and B2 phases, respectively. The modeling includes the solution phases and the stoichiometric Al21Pt5, Al 21Pt8, Al2Pt, Al3Pt2, AlPt, Al3Pt5 and AlPt2 intermetallic phases. The enthalpy of formation for the stoichiometric compounds and end-members of ordered L12 and B2 phases are calculated from first-principles study. In addition the enthalpies of mixing for the disordered fcc and bcc phases and the ordered L12 and B2 phases are calculated from first-principles study of special quasirandom structures. The obtained phase equilibria and thermodynamic properties are in good agreement with the experimental data in the literature as well as the first-principles calculations from the present work. © 2010 Elsevier Ltd. All rights reserved.

Korasie C.,NMISA | Eltawil A.,NIS
PTB - Mitteilungen Forschen und Prufen | Year: 2011

- 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.

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