Both Centro Nacional de Metrología (CENAM, Mexico) and PhysikalischTechnische Bundesanstalt (PTB, Germany) are national metrology institutes and provide the dissemination of the spectral directional emissivity as a calibration service. CENAM started this service recently. The emissivity measurement capability of PTB took part in two international comparisons performed in the past among other national institutes. The measurement instrumentation and techniques used for emissivity measurements at CENAM and PTB are both based on Fourier transform infrared spectrometers. Both setups are based on the principle of a spectral comparison of the radiances of the sample and blackbody radiator. In detail, the setups differ: CENAM has the capability of measuring the directional spectral emissivity normal to the sample surface, while PTB measures the directional spectral emissivity at angles of observation ranging from 5 • to 80 • , and provides the hemispherical spectral and total emissivity of samples as well. For this comparison, it was agreed to compare the value of the directional spectral emissivity normal to the sample surface obtained by CENAM with the one determined at an angle of 5 • by PTB. Four samples of different spectral directional emissivities were measured by the two institutes. For the samples, four copper disks with a diameter of 50 mm and a thickness of 5 mm were used. Three of them were coated with Comex 1402470 (white), 1402471 (aluminum), and 1402474 (black) paints, respectively, and the other one with Nextel 811-21 paint. Measurements were References to commercial products are provided for identification purposes only and constitute neither endorsement nor representation that the item identified is the best available for the stated purpose. obtained for each sample at a temperature of about 150 • C, and in the spectral range from 400 cm −1 to 2500 cm −1 (25 µm to 4 µm). The description of the experimental setups used and the comparison results are presented in this paper. It was found that the results obtained at CENAM and at PTB agree well within the declared standard uncertainties.
This paper presents a method to accurately determine the responsivity non-uniformity of the pixels of an infrared camera. Mandatory for the use of infrared cameras for measurements of radiance temperatures with small uncertainties is the knowledge of this responsivity non-uniformity and the resulting ability to correct the responsivity non-uniformity of the measured image. Infrared cameras are optically and electronically more complex than radiation thermometers. For the calibration of infrared cameras a large-area source with a known radiance distribution is required. Practical implementations of such large-area sources are plate radiators, which generally have a non-homogeneous distribution of the radiance and of the radiance temperature over their surface. The determination of the non-uniformity of the radiance temperature of a plate radiator is mandatory for the accurate calibration of infrared cameras, i.e. for the determination and adequate consideration of the responsivity non-uniformity of all pixels of an infrared camera.
This paper describes advances in measuring the characteristic spatial distribution of surface temperature and emissivity during laser-metal interaction under conditions relevant for laser powder bed fusion (LPBF) additive manufacturing processes. Detailed descriptions of the measurement process, results, and approaches to determining uncertainties are provided. Measurement uncertainties have complex dependencies on multiple process parameters, so the methodology is demonstrated on one set of process parameters and one material. Well-established literature values for high-purity nickel solidification temperature and emissivity at the solidification temperature were used to evaluate the predicted uncertainty of the measurements. The standard temperature measurement uncertainty is found to be approximately 0.9 % of the absolute temperature (16 °C), and the standard relative emissivity measurement uncertainty is found to be approximately 8 % at the solidification point of high-purity nickel, both of which are satisfactory. This paper also outlines several potential sources of test uncertainties, which may require additional experimental evaluation. The largest of these are the metal vapor and ejecta that are produced as process by-products, which can potentially affect the imaging quality, reflectometry results, and thermal signature of the process, while also affecting the process of laser power delivery. Furthermore, the current paper focuses strictly on the uncertainties of the emissivity and temperature measurement approach and therefore does not detail a variety of uncertainties associated with experimental controls that must be evaluated for future generation of reference data.
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