Spectral emissivity of surface blackbody calibrators

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    Abstract

    The normal spectral emissivity of commercial infrared calibrators is compared with measurements of anodized aluminum samples and grooved aluminum surfaces coated with Pyromark. Measurements performed by FTIR spectroscopy in the wavelength interval from 2 to 20 mu m and at temperatures between 5 and 550 degrees C are presented with absolute uncertainties from 0.25% to 1% in spectral regions with sufficient signal and no significant atmospheric gas absorption. A large variation in emissivity with wavelength is observed for some surfaces, i.e., from 1% to 3% to more than 10%. The variation in emissivity using similar materials can be reduced to 0.5-1% by optimizing the coating process and the surface geometry. Results are discussed and an equation for calculation of the equivalent blackbody surface temperature from FTIR spectra is presented, including reflected ambient radiation. It is in most cases necessary to correct temperature calibration results for calibrators calibrated at 8-14 mu m to obtain absolute accuracies of 0.1-1 degrees C in other spectral regions depending on the temperature. Uncertainties are discussed and equations are given for the correction of measured radiation temperatures.
    Original languageEnglish
    JournalInternational Journal of Thermophysics
    Volume28
    Issue number6
    Pages (from-to)2145-2154
    ISSN0195-928X
    DOIs
    Publication statusPublished - 2007

    Keywords

    • Blackbody
    • Calibration
    • Emissivity
    • FTIR
    • Infrared
    • Temperature

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