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South Africa

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.

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.

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.

Kocas I.,UME | Sabuga W.,PTB | Bergoglio M.,INRIM - Istituto Nazionale di Ricerca Metrologica | Eltawil A.E.,Nis | And 4 more authors.
PTB - Mitteilungen Forschen und Prufen | Year: 2011

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.

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.

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