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Realisation of ITS-90 fixed points and associated uncertainties

Realisation of ITS-90 fixed points and associated uncertainties. Bernard ROUGIE, Mohamed SADLI ( BNM-INM). Introduction. Black body and furnace technology Sources of uncertainty Uncertainty budget : ITS-90 and beyond. Furnace characteristics.

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Realisation of ITS-90 fixed points and associated uncertainties

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  1. Realisation of ITS-90 fixed pointsand associated uncertainties Bernard ROUGIE, Mohamed SADLI (BNM-INM) Workshop on uncertainties in radiation thermometry Paris,September 7, 2001

  2. Introduction • Black body and furnace technology • Sources of uncertainty • Uncertainty budget : ITS-90 and beyond Workshop on uncertainties in radiation thermometry Paris,September 7, 2001

  3. Furnace characteristics Heating element : Ni-Cr-Al (Kanthal), max. temperature 1300 °CTechnology : 3-zone furnace associated to three temperature controllersTemperature sensors : 3 Type S thermocouples Temperature stability < 0.1 °CTemperature uniformity < 0.3 °C over 80 mm (in the central region of the furnace) Workshop on uncertainties in radiation thermometry Paris,September 7, 2001

  4. Crucible dimentions 90 mm 75 mm 35 mm 1 mm 8 mm Material : High-purity (5N) graphite.Machining by especially dedicated tools (in order to minimize pollution)Dimensions : Solidity ensured by a “rounded” design of the inner edges of the most fragile parts.Additional parts (screw or ring) to support the cavity well from hydrostatic force.Wall thickness of the cavity is 0.9 mm. Workshop on uncertainties in radiation thermometry Paris,September 7, 2001

  5. Realisation of ITS-90 43 mm 700 mm Copper, gold or siver Workshop on uncertainties in radiation thermometry Paris,September 7, 2001

  6. Crucible filling-up set-up Silver 0.515 kg Gold 0.952 kg Copper 0.422 kg Workshop on uncertainties in radiation thermometry Paris,September 7, 2001

  7. Black body Other source Sources bench Aperture stop Field stop Grating Detectors Radiance comparator Workshop on uncertainties in radiation thermometry Paris,September 7, 2001

  8. Analysis of gold test piece Global purity : 0.99985 Measured from a spark spectrum Workshop on uncertainties in radiation thermometry Paris,September 7, 2001

  9. Impurities State of the art estimate for the uncertainty components caused by impurities and isotopes B. Fellmuth, J. Fischer, E..Tegeler • Basis of the estimates: • Standard deviations of the results near (CCT-k2) or at fixed points (CCT-K3, CCT K4) of the CIPM Key comparisons Fixed pointsGa InSnZnAlAg Estimate (mK) 0.2 0.8 0.5 0.7 1.5 4 Proposal: These guideline estimates should be used for uncertainty budgets if State-of-the-art high purity materials are used and no individual information on the impurity content is available. Workshop on uncertainties in radiation thermometry Paris,September 7, 2001

  10. Emissivity :Parameters and uncertainty Workshop on uncertainties in radiation thermometry Paris,September 7, 2001

  11. Metal at uniform temperature Sint :internal surface Sout =8 mm or 1 mm =0.05 sr 9 mm 75 mm Temperature gradient through crucible wall • Heat flow is constant at each point : wall thickness, inner temperature and outer temperature are uniform; radiation loss is uniform at each point • The solid angle of emission is determined by the output diaphragm of the cavity and the first diaphragm in front of it which is almost at the same temperature • Heat loss through output diaphragm is only due to radiation (no convection). It is computed by Stefan law. Workshop on uncertainties in radiation thermometry Paris,September 7, 2001

  12. through cavity wall Computation of temperature drop Sout : output surface Sint : internal surface e : wall thickness Rth : thermal resistivity 0 : flux lost Workshop on uncertainties in radiation thermometry Paris,September 7, 2001

  13. Value and uncertainty of temperature drop Workshop on uncertainties in radiation thermometry Paris,September 7, 2001

  14. Temperature uniformity Workshop on uncertainties in radiation thermometry Paris,September 7, 2001

  15. Freezing and melting plateau Workshop on uncertainties in radiation thermometry Paris,September 7, 2001

  16. Uncertainty budget ITS-90 fixed points Workshop on uncertainties in radiation thermometry Paris,September 7, 2001

  17. Uncertainty budget Future High temperature fixed points T=2600 K Workshop on uncertainties in radiation thermometry Paris,September 7, 2001

  18. Conclusion The major component of ITS-90 fixed points uncertainty is due to the plateau determination and its reproducibility. Improvements of temperature uniformity can reduce this term to 10 mK. The influence of metal purity is not easy to evaluate but not negligible. For the higher temperature fixed points, the gradient of temperature through cavity wall will be to evaluate accurately. Workshop on uncertainties in radiation thermometry Paris,September 7, 2001

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