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Radiation thermometry

Radiation thermometry. Uncertainties on measurements on Tungsten strip-lamps . Subject of interest. Strip. Base. Uncertainty budget. Phrase subject into context Sources (alphabetic order) Base temperature Current Drift Emissivity Positioning Quality of polynomial fit

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Radiation thermometry

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  1. Radiation thermometry Uncertainties on measurements on Tungsten strip-lamps

  2. Subject of interest Strip Base

  3. Uncertainty budget Phrase subject into context Sources (alphabetic order) • Base temperature • Current • Drift • Emissivity • Positioning • Quality of polynomial fit • Scale realization • Transmission of window 1. Derive its magnitude 2. Find order of importance

  4. Magnitude - Base temperature Base temperature has influence on temperature of strip and needs to be corrected for when deviating from Trefbase (Uncertainty 10%) • Minimize correction, water-cooled base: Tbase=(20±0.1)°C over entire range of operation • Magnitude 5 mK at 962°C • Type B evaluation

  5. Magnitude - Current Instruments involved • Current supply (stability I/I 5x10-5) • Zero-flux meter (equivalent I/I1x10-5) • Voltmeter (equivalent I/I  1x10-4, Keithley 181) • Magnitude 0.44 mA @ 4 A  54 mK at 962°C • Type A evaluation

  6. Magnitude - Drift Stability test: operate lamp for100 hrs @ 1700°C Requirement: T/t < 3 mK / hr over 100 hrs • History provides information on correction • Drift behaviour can be used to give an estimate of drift during calibration • Traceability route and context of measurement determines whether this source of uncertainty is relevant • Magnitude negligible • Type B evaluation

  7. Magnitude - Emissivity The emissivity () of Tungsten is involved when converting Trad from pyrometer to 650 nm. • Values () of de Vos are used • Only uncertainty in relative change of () is of importance; estimate 0.5% • Magnitude 3 mK at 962°C • Type B evaluation

  8. Vert. Rot. Hor. Rot. Hor. Magnitude - Positioning-1 • Displacement 2x horizontal, 1x vertical • Rotation around vertical/horizontal From profile measurements • Determine sensitivity around zero (%/mm, %/°) • Estimate uncertainty in determination of position • Magnitude 53 mK at 962°C • Type A evaluation

  9. Magnitude - Positioning-2 Total 0.06%  53 mK

  10. Magnitude - Quality of fit Polynomial fit: t90= ai ln(S), with a=0..5 Least squares residuals result in 26 mK • Magnitude 26 mK at 962°C • Type A evaluation

  11. Magnitude - Scale realization Standard pyrometer @ 650 nm • Magnitude 51 mK at 962°C • Type B evaluation

  12. Magnitude - Trans. window The transmission () of the window is involved when converting Trad from pyrometer to 650 nm. • Values () of Pyrex material are used • Only uncertainty in relative change of () is of importance; estimate 0.1% • Magnitude 1 mK at 962°C • Type B evaluation

  13. Order of importance

  14. EA-4/02 Expression of the uncertainty of Measurement in Calibration

  15. Conclusion • Uncertainty in measurements associated with Tungsten strip lamps is at NMi-VSL dominated by 4 contributions (1. Current) 2. Positioning 3. Scale realization 4. Quality of the fit • For NMi-VSL the overall uncertainty is evaluated to values for k=2 and 95% confidence interval:

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