Spectral Emissivity of Surface Blackbody Calibrators

摘要

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 deg C are presented with absolute uncertainties from 0.25percent to 1percent 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 1percent to 3percent to more than 10percent. The variation in emissivity using similar materials can be reduced to 0.5-1percent 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 deg C in other spectral regions depending on the temperature. Uncertainties are discussed and equations are given for the correction of measured radiation temperatures.