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Braunschweig, Germany

This report presents the results of the bilateral comparison on10 Ω and 100 kΩ resistance standards performed by the national metrology institutes of Georgia (GEOSTM) and Germany (PTB).

Richter S.,BAM Federal Institute of Materials Research and Testing | Sargent M.,LCG Group | Schiel D.,PTB | Kipphardt H.,BAM Federal Institute of Materials Research and Testing
Journal of Analytical Atomic Spectrometry | Year: 2013

Millions of measurements are performed each year by liquid based analytical atomic spectrometry to support healthcare, diagnostic tests, environmental monitoring, material assay, product development and safety. Despite the effort to develop absolute methods, most methods still depend on calibration solutions, which are gravimetric mixtures of high purity solvents and high purity (source material) metals or compounds. As in the real world ideal purity does not exist, the impurity of the solvent and the purity of the source material needs to be known. The impurity of a solvent with respect to one analyte can be measured rather easily and with low limits of determination. In contrast the measurement of the purity of the source material, i.e., the mass fraction of the main constituent in a high purity metal, is more difficult to determine. It becomes even more difficult when the source material is not a pure metal but a compound since problems regarding stoichiometry arise additionally. Although the major producers of calibration solutions make a special effort to determine the purity of the source material, the actual purity statement is often incomplete or not demonstrated. The main reason for this situation is the complexity and high effort necessary to fully characterize such a material. This problem holds to a very wide extent also for the primary standards for element determination at the National Metrology Institutes and Designated Institutes (NMIs and DIs). It is the task of the NMIs and DIs to realise and disseminate primary standards for providing traceability to the International System of Units (SI). The primary elemental standards at the NMIs should provide the link to secondary standards produced by commercial producers and other independently prepared standards for element determination. Without such primary standards, elemental calibration solutions may vary and, depending on the uncertainty required, comparability of measurement in time and space results cannot be achieved. © The Royal Society of Chemistry 2013.

News Article | November 5, 2015
Site: phys.org

Vector network analyzers (VNA) are among the most precise high-frequency measurement devices available today. Due to continuous development within the last decades VNAs are usable up to frequencies of 1 terahertz (1012 Hz) and complex error correction algorithms exist. However, VNAs are very expensive and require multiple frequency extenders in order to cover a wide frequency range. At the Physikalisch-Technische Bundesanstalt (PTB) a VNA has been developed which utilizes optoelectronic techniques based on femtosecond lasers. Such devices constitute a cost-effective alternative to conventional VNAs and might be used for high-frequency measurements in the future. The results have been published in the present issue of the renowned journal IEEE Transactions on Microwave Theory and Techniques.

The mirrors of these telescopes, which are used at temperatures below ‑190 °C, are made of special, ultrastable ceramics such as silicon carbide. In order to plan the exact dimensions correctly, even at such low temperatures, the precise thermal expansion of the materials used must be known. Within the scope of a recently completed ESA project, the Physikalisch-Technische Bundesanstalt (PTB) in Braunschweig measured the thermal expansion of these ceramics as well as that of single-crystal silicon in the temperature range from ‑266 °C to 20 °C with high accuracy. In vast parts of the temperature range investigated, the accuracy attained corresponds to a relative change in length of approx. one billionth per degree Celsius. The investigations have also shown that the values used to date for the reference material of "single-crystal silicon" must be corrected. The latest issue of the renowned scientific journal Physical Review B contains a report dedicated to the latter of these two subjects.Space telescopes such as Herschel explore spectral ranges that are not accessible from the Earth; they can therefore only be used in space. How critical it is to know the exact thermal expansion of the materials used when setting up such telescopes was clearly demonstrated during one of the latest ESA missions, as it was revealed that the simulations performed previously were not in agreement with the manufactured mirrors. The discrepancies were fortunately not discovered in space, but still led to unnecessary delays. To prevent such unpleasant surprises from recurring in the future, in-depth investigations of the materials used were required. For their investigations within the scope of the ESA project, René Schödel's research group used PTB's ultra-precise interferometer to measure the length of the samples across the whole temperature range with nanometer accuracy. This interferometer is the only one of its kind in the world. To allow measurements to be taken with similar accuracy but with less effort, even at other institutes, reference materials whose exact thermal expansion is known are usually used for comparison. One such reference material is single-crystal silicon, which is characterized by a continuous lattice structure with very few defects; it was also investigated by the researchers. Similar to some of the ultrastable ceramic materials, silicon exhibits a peculiar behavior: at low temperatures, it starts re-expanding below a certain temperature. This dynamic characteristic – which is rather unexpected in everyday life – was also exactly measured by the scientists from PTB. Their measurements yielded an important result: across a vast temperature range, they discovered significant deviations from the reference values used to date for single-crystal silicon. This suggests that the reference values must be corrected. The results of the project are of importance for further space missions that have already been planned, such as the James Webb Space Telescope (JWST), for which temperatures of use below ‑220 °C are planned, or the Space Infrared Telescope for Cosmology and Astrophysics (SPICA), for which even lower temperatures of use are envisaged. Explore further: Image: Simulating space for JWST's four infrared instruments More information: Thomas Middelmann et al. Thermal expansion coefficient of single-crystal silicon from 7 K to 293 K, Physical Review B (2015). DOI: 10.1103/PhysRevB.92.174113

Shore P.,Cranfield University | Cunningham C.,UK ATC | Debra D.,Stanford University | Evans C.,Zygo Corporation | And 5 more authors.
CIRP Annals - Manufacturing Technology | Year: 2010

The fields of astronomy and gravitational science have presented significant precision engineering challenges. Numerous solutions for these fields of science have achieved unprecedented levels of accuracy, sensitivity and sheer scale. Notwithstanding of their importance to science understanding, many of these precision engineering developments have become key enabling technologies for wealth generation and other human well-being issues. This paper provides a brief historical overview of astronomy and gravitational instruments. Later, details of critical precision engineering developments that supported the establishment of leading astronomical and gravitational instruments are illustrated. Details of specific developments having wider application to the benefit of mankind are provided. Finally, significant precision engineering demands to enable future science programmes are introduced. © 2010 CIRP.

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