A Facility for Spectral Emissivity Measurement under Vacuum for Industrial and Remote Sensing Applications

Abstract

A variety of techniques for the measurement of emissivity is available today but in many cases these techniques do not adequately meet the wide range of requirements posed by modern science and industry. Furthermore, they do not provide sufficiently accurate results and lack reliable and traceable uncertainties. Therefore, a measurement setup and a validated method for highly accurate directional spectral emissivity, total directional emissivity and total hemispherical emissivity measurements under vacuum in the wavelength range from 4 µm to 100 µm and a temperature range from -40 °C to 600 °C with validated uncertainties was developed at the Physikalisch-Technische Bundesanstalt (PTB). Using a direct radiometric method with two reference blackbodies, the measurements at this facility, the Reduced Background Calibration Facility (RBCF), are traceable to the International Temperature Scale of 1990 (ITS-90).

High-Accuracy Emissivity Data on the Coatings Nextel 811-21, Herberts 1534, Aeroglaze Z306 and Acktar Fractal Black

“…The emissivity measurements of the black coatings were taken at two setups at PTBunder vacuum at the RBCF and in air at the EMAF-by applying the measurement schemes and data, and uncertainty evaluation described shortly above and described in detail in [1][2][3]6,7]. Two sets of detectors and beamsplitters were used with the IR-FTS according to the wavelength and temperature range of the measurements.…”

“…Highly accurate measurements of directional spectral, directional total and hemispherical total emissivities for four widely used black coatings-Nextel 811-21, Herberts 1534, Aeroglaze Z306 and Acktar Fractal Black-were taken by PTB in the wavelengths range from 4 µm to 100 µm at different temperatures in the range from 25 • C to 150 • C. The achieved absolute standard uncertainty (k = 1) is calculated according to [5][6][7]. It is 0.005 or better for measurements at high temperatures (T = 120 • C and T = 150 • C) and it is better than 0.022 (for some measurements better than 0.011) for measurements at 25 • C. It should be noted that the achieved uncertainty significantly depends on the experimental conditions and the investigated coating.…”

“…Furthermore, the uncertainty budget is calculated for each individual measurement, since the relevance of the individual uncertainty contributions depends significantly on the conditions of the measurement and the sample investigated. A detailed description of the data evaluation procedure and the uncertainty calculation is given in [6,7].…”