National Metrology Institute Of South Africa Research Articles

AFRIMETS.EM-S2: comparison on digital multimeter for DC voltage, DC current, DC resistance, AC voltage and AC current parameters

Main textDuring the 13th intra-Africa metrology system (AFRIMETS) technical committee on electricity and magnetism (TCEM) meeting held on 8th to 9th of July 2019 at Giza, Egypt, a supplementary comparison was approved on a digital multimeter. The primary aim of the comparison is to support the calibration measurement capabilities of the national metrology institutes in measuring DC voltage, DC current, DC resistance, AC voltage and AC current parameters. The National Institute of Standards, Egypt (NIS) piloted the comparison and National Metrology Institute of South Africa (NMISA) provided the comparison reference values and eight AFRIMETS national metrology designated institutes participated. The comparison commenced in January 2020 and completed in August 2021. This report describes the behaviour of the comparison standard, participants reported corrections and calculated comparison reference values with associated uncertainties of measurements at 95% confidence level, normalized errors and degrees of equivalence.To 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 https://www.bipm.org/kcdb/.The final report has been peer-reviewed and approved for publication by the CCEM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Report on the CCM.T-K2.1 Key Comparison, Measurand Torque: 10 kN∙m and 20 kN∙m, Final Report

Main textThe comparison of torque in the range of 10 kN m and 20 kN m was organized and conducted between two laboratories, the National Metrology Institute of Japan (NMIJ) in the National Institute of Advanced Industrial Science and Technology (AIST) in Japan, and the National Metrology Institute of South Africa (NMISA) in South Africa. This comparison aims to link the national torque standards in South Africa to CCM.T-K2 so that NMISA can achieve the degree of equivalence (DOE) of the CMCs of its torque standards. NMIJ, which had joined CCM.T-K2 key comparison in 2008, played a role of a link laboratory. The results of this comparison showed a good agreement in the NMISA's results with the KCRV.To 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 https://www.bipm.org/kcdb/.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).

AFRIMETS.EM-S1 supplementary comparison of resistance standards

Main textAFRIMETS.EM-S1 supplementary comparison on resistance standards at 1 Ω, 10 Ω, 100 Ω, 1 kΩ and 10 kΩ commenced November 2015 and ended June 2018. The comparison approved by AFRIMETS technical committee for Electricity and Magnetism (TC-EM) and Consultative Committee for Electricity and Magnetism (CCEM). Seven National Metrology Institutes participated including National Metrology Institute of South Africa (NMISA)the pilot laboratory. The primary objective of the comparison is aimed to underpin and strengthen the capabilities of the National Metrology Institutes and establish the degree of equivalence and comparability. The results of the participants are found to be equivalent, comparable and in agreement with the comparison reference values within stated uncertainties of measurements.To 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 https://www.bipm.org/kcdb/.The final report has been peer-reviewed and approved for publication by the CCEM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Final report of AFRIMETS.M.D-S4 - hydrometer calibrations

Main textA supplementary comparison for hydrometer calibration using Cuckow's method was proposed during the 10th AFRIMETS Committee for Mass and Related Quantities (TCM) meeting held at the National Institute of Standards (NIS, Egypt). Two laboratories only from AFRIMETS, NIS and the National Metrology Institute of South Africa (NMISA), had the capacity to participate in the comparison. Generously, Centro Nacional de Metrologia (CENAM, Mexico) accepted to participate in the comparison and provided reference values. This comparison, designated as AFRIMETS.M.D-S4, was coordinated by the NIS supported by all participants. The corrections to be applied to three stated scale readings at 20 °C of different transfer standards in the density range between 0.600 g/cm3 to 1.300 g/cm3 were determined. NIS carried out the measurement at the beginning and at the end of the comparison.To 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 https://www.bipm.org/kcdb/.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).

The operation of an ionization chamber with depleted gas for radioactivity measurement: Calibration procedure and utilising normalized manufacturer's radionuclide factors

At the National Metrology Institute of South Africa (NMISA) absolute activity measurements of γ-emitting radionuclides are maintained for longevity on a secondary standard ionization chamber. Because the ionization chamber has lower gas pressure than that normally produced by the manufacturer, this paper focuses attention on explaining a normalization scheme devised to allow NMISA to make use of the manufacturer's supplied radionuclide calibration factors when necessary. The applicability of the procedure is justified through analysis of some results from a comprehensive simulation of the chamber undertaken in an independent study. Comparisons of the derived normalized calibration factors against those obtained through measurement at NMISA are made for a variety of radionuclides.

A comparison of different calibration strategies for the trace analysis of soil samples by inductively coupled plasma mass spectrometry (ICP-MS)

The National Metrology Institute of South Africa (NMISA) is expanding its capabilities in the field of the analysis of trace and ultra-trace levels of toxic and minor elements in environmental samples, with a special focus on soils to support projects of the University of Pretoria (UP) in the field of veterinary geology for the One Health Platform. The most accurate calibration strategy developed by the laboratory involves double isotope dilution analysis, where a stable isotope standard of the element of interest is used as the ideal internal standard. External calibration is the most commonly used calibration strategy for elemental analysis. To reduce the impact of instrumental drift on the accuracy of the measurement results, nominally the same amount of an internal standard is added to the samples and the standards. Standard addition is a calibration strategy that could eliminate the issue of matrix effects for trace and ultra-trace elemental analysis, because the calibration standards are added as spikes to aliquots of the sample to prepare the calibration curve. The purpose of the study was to compare the results obtained for the analysis of trace elements in soil samples using the calibration strategies of isotope dilution analysis; gravimetric external calibration with gravimetric internal standardisation; as well as gravimetric standard addition with gravimetric internal standardisation. The aim was to show that the application of gravimetric preparation to the more routine calibration approaches of external calibration and standard addition could achieve very comparable results and associated measurement uncertainties to isotope dilution analysis. The application of gravimetric sample preparation could assist routine laboratories, that have significant resource constraints, to improve the accuracy of their measurement results. These approaches could also be used in the experimental homogeneity and stability studies required for the production of reference materials, where high precision methods are required.

Development of ultrastable fiber-optic time and frequency reference networks in Africa.

The unparalleled accuracy of modern-day atomic clocks has stimulated the development of time and frequency comparison techniques, with optical frequency transfer over fiber networks emerging as the preferred method. It has been demonstrated that frequency transfer over optical fibers has an order-of-magnitude better stability and accuracy than traditional satellite-based techniques. Precise time has become an essential service for most critical infrastructure and applications. New progress in LTE and 5G will demand more access to precise time with accuracies of under 10 ns. Although this technology exists in Africa, continuous improvements are required. With the arrival of the Square Kilometre Array (SKA) in Africa, the National Metrology Institute of South Africa (NMISA) upgraded its time and frequency infrastructure in order to support the stringent time accuracy requirements of the MeerKAT and SKA telescopes. Over the past five years, the Centre for Broadband Communication at the Nelson Mandela University has been conducting exciting and cutting-edge research looking at new and innovative ways for coherently disseminating high-speed data and clock over optical fiber networks. This paper reports on recent research progress made in developing synchronous optical networks in South Africa and across the African continent. This paper begins by presenting a pioneering all-optical approach for measuring the round-trip latency time along a spooled G.652 single-mode fiber. This has been realized by optically injecting a pulse-per-second (PPS) signal from a distributed feedback laser into the slave mode of a 1550 nm vertical cavity surface emitting laser (VCSEL) located at the receiver end. A round-trip fiber time delay of 113.2 µs was experimentally measured over 22 km. Furthermore, the jitter instability of an optically modulated PPS was measured as a function of temperature. A jitter of 434.82 ps was measured during the night-to-day temperature cycle (5°C-25°C). The impact of polarization fluctuations on jitter stability is presented. A maximum jitter of 417.88 ps was measured for the transmitted PPS along the aerial fiber. Lastly, a novel technique for distributing a stable microwave reference frequency, using an intensity modulated VCSEL, is presented. The novel frequency dissemination and synchronization system proposes the use of a VCSEL-based phase correction actuator together with the inherent chromatic dispersion properties of the fiber. Frequency instabilities of 4.18939×10-12 at 104s without active noise cancellation and 4.86×10-14 at 104s with active noise cancellation were successfully measured across the 26 km G.655 fiber link.

Final report on AFRIMETS supplementary comparison AFRIMETS. T-S2): platinum resistance thermometer and digital thermometer calibrations over the range -50 °C to 450 °C

A Regional Metrology Organization (RMO) supplementary comparison of platinum resistance thermometer and digital thermometer (AFRIMETS.T-S2) was carried out among AFRIMETS member NMIs namely the National Metrology Institute of South Africa (NMISA), Laboratoire Public d'Essais et d'Etudes - Laboratoire National de Métrologie (LPEE-LNM), Ghana Standards Authority (GSA), and Agence Burkinabé de Normalisation, de la Métrologie et de la Qualité (ABNORM) between Dec 2015 and Sept 2018. The temperature range of the inter comparison is -50 °C to 450 °C. The results of this comparison are reported in this document, along with descriptions of the Artefacts and devices used during measurement. This report also presents the uncertainty budget. The results are analysed and En values are reported.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 CCT, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

South African pilot study: End-to-end radiotherapy and medical physics dosimetry audits

Background: The National Metrology Institute of South Africa (NMISA), as an institute responsible for disseminating traceability, has embarked on establishing a national dosimetry audit programme with assistance from the International Atomic Energy Agency (IAEA). Dosimetry audits in South Africa are carried out through the IAEA using mailed thermoluminescents. Onsite dosimetry is not performed in South Africa but the IAEA has provided a dosimetry kit to NMISA to facilitate the audits. The kit consists of a Farmer type PTW 30012 ionisation chamber for photon beams and an Advanced Markus PTW 34045 chamber for electron beams with a water phantom and a Perspex plate phantom. End-to-end audits are also not performed or, if performed, they are not monitored officially in South Africa; however, the IAEA also provided a CIRS IMRT thorax phantom which can be used nationally. Aim: To test the establishment of radiotherapy and medical physics dosimetry audits at pilot centres in South Africa. Setting: NIMISA was tasked by IAEA to establish radiotherapy and medical physics dosimetry audits. A calibration kit was supplied by the IAEA for dosimetry measurement and a CIRS IMRT thorax phantom was also supplied by the IAEA for end-to-end measurements. Five hospitals were identified by the steering committee as pilot centres to test the establishment of the dosimetry audits. Methods: The audit measurements for reference beams were carried out using a Farmer type PTW 30012 ionisation chamber for photon beams and an Advanced Markus PTW 34045 chamber for electron beams with a water phantom and a Perspex plate phantom, respectively. End-to-end audits, which involved computed tomography (CT) scanning, treatment planning and treatment delivery with dose measurements, were carried out using a CIRS IMRT thorax phantom. The planning staff or the medical physicists were requested to image the phantom and create a treatment plan according to a procedure provided by the researcher on their institutional treatment planning system. On completion, the approved plan was delivered at the treatment unit by setting up the phantom and measuring the doses with an ionisation chamber at different specified reference points. Results: For photon beam reference dosimetry, variations between 0.5% and 2.48% were observed, and for electron beams, variations of up to 8.0% were observed. For end-to-end audits, variations of up to 7.1% were observed between the calculated and measured doses. Conclusion: The pilot audits provided a platform to formulate and validate the audit methodologies required for the establishment of a national end-to-end dosimetry audit programme.

The Importance of Establishing a Very High-Temperature Radiation Thermometry Measurement Capability at the National Metrology Institute of South Africa (NMISA)

The ITS-90 scale above the Silver (Ag) point is realized using a standard linear radiation thermometer by measurement at a reference point which is an Ag, Gold (Au), or Copper (Cu) point. The fixed...

Final report, on-going key comparison BIPM.QM-K1, ozone at ambient level, comparison with NMISA, June 2017

As part of the on-going key comparison BIPM.QM-K1, a comparison has been performed between the ozone national standard of South Africa maintained by the National Metrology Institute of South Africa (NMISA) and the common reference standard of the key comparison, maintained by the Bureau International des Poids et Mesures (BIPM), via a transfer standard maintained by the National Institute of Standards and Technology (NIST). The instruments have been compared over a nominal ozone amount-of-substance fraction range of 0 nmol/mol to 500 nmol/mol.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 CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Final report, on-going key comparison BIPM.QM-K1, ozone at ambient level, comparison with NMISA, June 2017

As part of the on-going key comparison BIPM.QM-K1, a comparison has been performed between the ozone national standard of South Africa maintained by the National Metrology Institute of South Africa (NMISA) and the common reference standard of the key comparison, maintained by the Bureau International des Poids et Mesures (BIPM), via a transfer standard maintained by the National Institute of Standards and Technology (NIST). The instruments have been compared over a nominal ozone amount-of-substance fraction range of 0 nmol/mol to 500 nmol/mol.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 CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Final report of AFRIMETS.M.M-S6: supplementary comparison of 100 mg, 100 g 500 g, 1 kg and 5 kg stainless steel mass standards

This report summarizes the results of AFRIMETS.M.M-S6 mass standards comparison conducted between eleven participating laboratories/countries. Two sets of five weights with nominal values 100 mg, 100 g, 500 g, 1 kg and 5 kg were used as the traveling standards. These nominal values were decided from the needs of participating laboratories submitted to the pilot laboratory through a questionnaire and agreed upon by all participants. The traveling standards were hand carried between laboratories starting from February 2014 and were received from the last participants in October 2014. The programme was coordinated by National Metrology Institute of South Africa (NMISA), who provided the travelling standards and reference values for the comparison. The corrections to the BIPM as-maintained mass unit [5] have insignificant influence on the results of this comparison.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).

Final report on AFRIMETS comparison of liquid in glass thermometer calibrations from −35 °C to 250 °C

A Regional Metrology Organization (RMO) supplementary comparison of liquid in glass thermometer (AFRIMETS.T-S5) was carried out by the National Metrology Institute of South Africa (NMISA), Zimbabwe Scientific & Industrial Research & Development Centre—National Metrology Institute (SIRDC-NMI), Zambia Bureau of Standards (ZABS), Botswana Bureau of Standards (BOBS), Namibian Standards Institute (NSI), Mauritius Standards Bureau (MSB) and Seychelles Bureau of Standards (SBS) between January and September 2016. The temperature range of the inter comparison is −35 °C to 250 °C. The results of this comparison are reported here, along with descriptions of the Artefacts used. This report also presents the uncertainty budget of each participant. The results are analysed and normalized error (En) values are reported.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 CCT, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Report on AFRIMETS supplementary comparison: platinum resistance thermometer and digital thermometer calibrations against ITS-90 over the range -50 °C to 450 °C (AFRIMETS.T-S1)

A Regional Metrology Organization (RMO) supplementary comparison of platinum resistance thermometer and digital thermometer (AFRIMETS.T-S1) was carried out by the National Metrology Institute of South Africa (NMISA), National Institute for Standards Egypt (NIS), National Metrology Institute of Ethiopia (NMIE), Kenya Bureau of Standards (KEBS), National Institute of Metrology Thailand (NIMT), Uganda National Bureau of Standards (UNBS), Tanzania Bureau of Standards (TBS), Mauritius Standards Bureau (MSB) and Seychelles Bureau of Standards (SBS) between March 2008 and October 2010. The temperature range of the inter comparison is -50 °C to 450 °C. The results of this comparison are reported here, along with descriptions of the Artefacts and devices used during measurement. This report also presents the uncertainty budget. The results are analysed and normalized error (En) values are reported.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 CCT, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

O29. International comparisons of activity measurements of Tc-99m and F-18

Introduction The short-lived radionuclides Tc-99m and F-18 are used in nuclear medicine for imaging purposes. Hospitals must accurately measure the activity of radiopharmaceuticals administered to patients with a radionuclide activity calibrator which is traceable to a national metrology institute via calibration sources. The International Reference System Transfer Instrument (SIRTI) was recently used by the International Bureau of Weights and Measures (BIPM) to measure the activity of Tc-99m and F-18 sources prepared at the National Metrology Institute of South Africa (NMISA). These on-site measurements were compared with those made with the calibrated NMISA ionisation chamber (IC). Through comparisons such as these, equivalence to international metrology institutes and quality of measurements are demonstrated. This presentation describes the comparison process. Materials and methods The SIRTI is a portable NaI(Tl) well counter used for on-site measurements of short-lived radionuclides at metrology institutes. In preparation for these comparisons, Tc-99m and F-18 were standardized by NMISA via the 4 π β γ liquid scintillation coincidence counting method. The results from the primary standardizations were transferred to the NMISA IC via primary standardized liquid sources. The current produced by gamma radiation emitted from these sources was used to determine calibration factors for Tc-99m and F-18. For the SIRTI comparisons, master solutions of Tc-99m and F-18 were prepared from new batches of material. From each master solution, one source was made for measurement with the NMISA IC and three for measurement with the SIRTI. The NMISA IC and calibrated balances were used to determine the activity concentration of each master solution. Using these values, the activities of the SIRTI sources were calculated and compared to the actual SIRTI measured activities. Results Comparison results for NMISA show agreement, within uncertainties, with the international reference values previously established for Tc-99m and F-18. Conclusion Good results from both comparisons ensure the quality of measurements and services provided via the NMISA IC for Tc-99m and F-18.

P5. Hands-on radionuclide activity meter (dose calibrator) training at NMISA

Introduction Radionuclide activity meters (commonly known as dose calibrators) are used to accurately measure the activity of radionuclide solutions used in nuclear medicine. Medical physicists are required to frequently check the accuracy of hospital dose calibrators by measuring calibration sources, the results of which must be within 10% accuracy to be deemed acceptable. Administering inappropriate amounts of radioactivity to a patient can result in ineffective treatment. Materials and methods The National Metrology Institute of South Africa (NMISA) is offering training to honours and fourth year medical physics students through a project on dose calibrator measurements. The objective is to identify and calculate the activity and corresponding uncertainties of a mixture of three unknown gamma emitting radionuclides contained in a solution. The student will be required to identify each radionuclide after measuring a spectrum with a high purity germanium (HPGe) detector. Using the NMISA ionisation chamber and electrometer, the student will be required to measure the current produced by gamma radiation emitted from a standard source of each of the identified radionuclides and calculate the corresponding calibration factors, with uncertainties. The student will be required to measure the total current produced by the three radionuclides over a period of one to two months and extract the activity of each radionuclide by deconvolution and using the calibration factors determined. An uncertainty budget will be compiled for each radionuclide. Results The project feasibility has been demonstrated through simulation of the current produced by a mixture of Ga-67, I-131 and Fe-59 over a period of one month. Statistical variation was included by altering the simulated total current appropriately, and an uncertainty on each data point was added, both procedures following a Gaussian distribution between 0 and 0.5%. The extracted activities showed agreement within 3 standard deviations, with 3% discrepancy from the expected values. Conclusion Students will receive relevant hands-on training, a requirement to become a medical physicist.

How well do our measurements measure up? An overview of South Africa’s first proficiency testing scheme for organochlorine pesticides in water

Access to safe drinking water is a basic human right in South Africa. Therefore, the accurate measurement of water quality is critical in ensuring the safety of water prior to its intended use. Proficiency testing schemes (PTSs) are a recognised form of assessing the technical competence of laboratories performing these analyses. There are over 200 water testing laboratories in South Africa, with only 51 being accredited for testing some or all parameters (physical, chemical and microbiological content) prescribed in SANS 241. Only a limited number of laboratories test for organic contaminants, as this requires advanced, costly analytical instrumentation, such as GC-FID/ECD/MS and LC-UV/MS, as well as skilled staff. These laboratories are either looking at selected organic contaminants listed in the World Health Organisation (WHO) drinking water guidelines or performing the minimum requirements, as stipulated in SANS 241, for phenols, atrazine, trihalomethanes and total dissolved organic content. Whereas several local PTS providers are addressing the competent assessment of microbiological, physical and inorganic chemical testing of water, a clear need for a South African PTS provider for organic contaminant analysis in water was identified by NMISA (National Metrology Institute of South Africa) in 2012. The key drivers for the coordination of a local PTS stem mainly from the limited stability of analytes in the samples for analysis and the high cost and logistics of international PTS participation. During 2012 and 2013, NMISA conducted a PTS trial round, a workshop and 2 additional PTS rounds for organochlorine pesticides in water, for South African laboratories, and also several international participants from other countries in Africa. This paper will highlight some of the challenges faced by laboratories when analysing organochlorine pesticides at the ng/l concentration level. Issues surrounding the comparability of measurement results, traceability, method validation and measurement uncertainty are also discussed.

Activity determination of 59Fe by 4π beta–gamma counting using liquid scintillation in the beta channel

This paper reports on absolute activity measurements of iron-59 made at the National Metrology Institute of South Africa (NMISA) via 4π(LS)β–γ coincidence counting. The exercise formed part of an Asia Pacific Metrology Program (APMP) regional key comparison. Source data were analysed by the extrapolation technique for a number of gamma-ray window settings. In addition, a feasibility study was undertaken on a second technique; a non-extrapolation method based on a detection efficiency analysis. The reported activity concentration of the 59Fe solution was determined with a relative uncertainty of 0.28% (k=1), the uncertainty being due mainly to the rate vs. efficiency fitting process. The result from the non-extrapolation method was lower than that given by extrapolation by 0.33%, within two standard deviations. Possible reasons for the small discrepancy are discussed.

Accelerometer transverse sensitivity calibration; validation and uncertainty estimation

The National Metrology Institute of South Africa (NMISA) has implemented a system to measure the transverse sensitivity of vibration transducers. As a mechanical device, the principle sensing axis of an accelerometer is not 100 % perpendicular to the mounting axis. This gives rise to the effect that the accelerometer will produce an electrical output even when a mechanical input perpendicular to the principle measurement axis is applied. The quantification of this "defect" parameter is of importance when high accuracy acceleration measurements are performed using accelerometers. This paper gives a brief overview of the system developed by the NMISA to measure the transverse sensitivity of vibration transducers. The paper then explores the validation of the system along with the uncertainty of measurement associated with the calibration system.