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 Turning entanglement upside down
22.05.2018 | Universität Innsbruck

nachricht Astronomers release most complete ultraviolet-light survey of nearby galaxies
18.05.2018 | NASA/Goddard Space Flight Center

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: LZH showcases laser material processing of tomorrow at the LASYS 2018

At the LASYS 2018, from June 5th to 7th, the Laser Zentrum Hannover e.V. (LZH) will be showcasing processes for the laser material processing of tomorrow in hall 4 at stand 4E75. With blown bomb shells the LZH will present first results of a research project on civil security.

At this year's LASYS, the LZH will exhibit light-based processes such as cutting, welding, ablation and structuring as well as additive manufacturing for...

Im Focus: Self-illuminating pixels for a new display generation

There are videos on the internet that can make one marvel at technology. For example, a smartphone is casually bent around the arm or a thin-film display is rolled in all directions and with almost every diameter. From the user's point of view, this looks fantastic. From a professional point of view, however, the question arises: Is that already possible?

At Display Week 2018, scientists from the Fraunhofer Institute for Applied Polymer Research IAP will be demonstrating today’s technological possibilities and...

Im Focus: Explanation for puzzling quantum oscillations has been found

So-called quantum many-body scars allow quantum systems to stay out of equilibrium much longer, explaining experiment | Study published in Nature Physics

Recently, researchers from Harvard and MIT succeeded in trapping a record 53 atoms and individually controlling their quantum state, realizing what is called a...

Im Focus: Dozens of binaries from Milky Way's globular clusters could be detectable by LISA

Next-generation gravitational wave detector in space will complement LIGO on Earth

The historic first detection of gravitational waves from colliding black holes far outside our galaxy opened a new window to understanding the universe. A...

Im Focus: Entangled atoms shine in unison

A team led by Austrian experimental physicist Rainer Blatt has succeeded in characterizing the quantum entanglement of two spatially separated atoms by observing their light emission. This fundamental demonstration could lead to the development of highly sensitive optical gradiometers for the precise measurement of the gravitational field or the earth's magnetic field.

The age of quantum technology has long been heralded. Decades of research into the quantum world have led to the development of methods that make it possible...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Save the date: Forum European Neuroscience – 07-11 July 2018 in Berlin, Germany

02.05.2018 | Event News

Invitation to the upcoming "Current Topics in Bioinformatics: Big Data in Genomics and Medicine"

13.04.2018 | Event News

Unique scope of UV LED technologies and applications presented in Berlin: ICULTA-2018

12.04.2018 | Event News

 
Latest News

Designer cells: artificial enzyme can activate a gene switch

22.05.2018 | Life Sciences

PR of MCC: Carbon removal from atmosphere unavoidable for 1.5 degree target

22.05.2018 | Earth Sciences

Achema 2018: New camera system monitors distillation and helps save energy

22.05.2018 | Trade Fair News

VideoLinks
Science & Research
Overview of more VideoLinks >>>