The determination of the uncertainties of spectral emissivity measurements in air at the PTB

Abstract

The instrumentation of the Physikalisch-Technische Bundesanstalt (PTB) for the measurement of the directional spectral emissivity in air in the temperature range from 80 • C to 400 • C and wavelength range from 4 µm to 40 µm and the subsequent procedures for data evaluation are described. Special emphasis is placed on the calculation of the uncertainty of the directional spectral emissivity and of the uncertainty of the sample surface temperature. For samples with typical emissivities of about 0.6, absolute expanded uncertainties (k = 2) of 0.01 can be reached at a surface temperature of 200 • C in the spectral range from 5 µm to 40 µm. However, it is also shown that-due to the complex dependence of the uncertainty on the sample and the conditions of measurement-general statements about the uncertainty cannot be given. The uncertainty of the emissivity has to be calculated for each individual case of sample and temperature.

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.…”

“…The uncertainty of the directional spectral emissivity is calculated via a Monte-Carlo method [5,6] based on the final determination equation of the directional spectral emissivity and is spectrally dependent. 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.…”

“…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].…”

A Terahertz Blackbody Radiation Standard Based on Emissivity Measurements and a Monte-Carlo Simulation

“…Furthermore, a second reference blackbody of significantly different temperature from the first reference blackbody is generally applied for the correction of the background signal. The instrumentation and the associated uncertainties of this measurement principle are published in detail in [7][8][9], respectively. To determine the angular dependency of the directional spectral emissivity from a series of the above described ratio measurements the sample can be tilted in a range from 5°to 70°between the sample surface normal and the direction of observation.…”