Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Spectral emissivity measurements for radiation thermometry

28.05.2008
Industry and research are increasingly relying on non-contact temperature measurements with the aid of heat radiation, for example, for the reliable and reproducible drying of car paint.

In order to attain exact and reliable results, the emissivity of the measured surface has to be known. It can only be determined precisely in complex measuring facilities. The Physikalisch-Technische Bundesanstalt (PTB) has developed a modern emissivity measuring facility for industry-oriented calibrations.

Today, the accuracy of industrial temperature measurements carried out with contact-free radiation thermometers, is often no longer limited by the quality of the radiation thermometers, but rather by insufficient knowledge of the emissivity of the surface observed. Industrial radiation thermometers can furnish a resolution of up to 20 mK, with an uncertainty of 1 K for temperature measurements of 100 °C. In contrast to this, the directional spectral emissivities of surfaces can often only be specified with standard measurement uncertainties of 5 %. When measuring a temperature of 100 °C in the spectral range by around 10 µm, this corresponds to a temperature uncertainty of typically 5 K.

The emissivity is not a constant, but rather changes in general with changes of the surface (roughness, oxidation, impurities etc.), the observation angle, the observation wavelength as well as the temperature. Furthermore, it is often distributed inhomogeneously over the surface. Precise temperature measurements therefore demand exact knowledge of the emissivity. To determine the variety of dependencies of the emissivity on the above-mentioned parameters, complex measuring facilities are necessary.

The spectral emissivity is measured in the PTB by comparing the radiances of a cavity radiator of high quality – resembling an almost ideal black body – with the sample to be investigated by means of a Fourier transform spectrometer, whereby the radiation of the environment and the inherent radiation of the spectrometer are taken into consideration. Holding the sample in a temperature-regulated hemisphere hereby guarantees a constant radiation exchange with the environment. The apparatus allows the determination of the directional spectral emissivity as well as of the total emissivity of opaque samples under ambient conditions in a temperature range from 80 °C to 250 °C and a wavelength range from 4 µm to 40 µm under emission angles of 5° to 70° with a relative standard measurement uncertainly of better than 2 %. The extrapolation of the measured values of the directed spectral emissivity for emission angles above 70° then allows the hemispherical spectral emissivity, which is especially important for calculations of the net radiation exchange, as well as the total emissivity to be calculated. The homogeneity of the directional spectral emissivity at 4 µm is determined with the help of a thermography camera.

The results of the first orders from customers have served, for example, to optimise the paint drying process in the automobile industry, the thermal design of furnaces as well as the monitoring of glass forming processes.

Another measuring facility is currently being set up in the PTB which will allow emissivity measurements to be performed under vacuum conditions in an extended temperature and wavelength range – in particular for space applications.

This text in the latest issue of PTB-news (08.2):
http://www.ptb.de/en/publikationen/news/html/news081/artikel/0813.htm
Contact:
Dr. Christian Monte, PTB Working Group 7.31 High-temperature Scale, Phone +4930-3481-7246, e-mail: christian.monte@ptb.de

Erika Schow | alfa
Further information:
http://www.ptb.de/en/aktuelles/archiv/presseinfos/pi2008/pitext/pi080527.html

More articles from Physics and Astronomy:

nachricht Tracing aromatic molecules in the early universe
23.03.2017 | University of California - Riverside

nachricht New study maps space dust in 3-D
23.03.2017 | DOE/Lawrence Berkeley National Laboratory

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Giant Magnetic Fields in the Universe

Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.

The results will be published on March 22 in the journal „Astronomy & Astrophysics“.

Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...

Im Focus: Tracing down linear ubiquitination

Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.

Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...

Im Focus: Perovskite edges can be tuned for optoelectronic performance

Layered 2D material improves efficiency for solar cells and LEDs

In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...

Im Focus: Polymer-coated silicon nanosheets as alternative to graphene: A perfect team for nanoelectronics

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...

Im Focus: Researchers Imitate Molecular Crowding in Cells

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

International Land Use Symposium ILUS 2017: Call for Abstracts and Registration open

20.03.2017 | Event News

CONNECT 2017: International congress on connective tissue

14.03.2017 | Event News

ICTM Conference: Turbine Construction between Big Data and Additive Manufacturing

07.03.2017 | Event News

 
Latest News

When Air is in Short Supply - Shedding light on plant stress reactions when oxygen runs short

23.03.2017 | Life Sciences

Researchers use light to remotely control curvature of plastics

23.03.2017 | Power and Electrical Engineering

Sea ice extent sinks to record lows at both poles

23.03.2017 | Earth Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>