Featured Research

from universities, journals, and other organizations

Spectral Emissivity Measurements For Radiation Thermometry

Date:
May 28, 2008
Source:
Physikalisch-Technische Bundesanstalt
Summary:
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. Now researchers have developed a modern emissivity measuring facility for industry-oriented calibrations.

Local variation of the directed spectral emissivity ελ of a car paint sample at a wavelength of 4 micro;m, measured using a thermography camera.
Credit: Image courtesy of Physikalisch-Technische Bundesanstalt (PTB)

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.

Related Articles


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 m, 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 m to 40 m 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 m 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.


Story Source:

The above story is based on materials provided by Physikalisch-Technische Bundesanstalt. Note: Materials may be edited for content and length.


Cite This Page:

Physikalisch-Technische Bundesanstalt. "Spectral Emissivity Measurements For Radiation Thermometry." ScienceDaily. ScienceDaily, 28 May 2008. <www.sciencedaily.com/releases/2008/05/080528095657.htm>.
Physikalisch-Technische Bundesanstalt. (2008, May 28). Spectral Emissivity Measurements For Radiation Thermometry. ScienceDaily. Retrieved November 26, 2014 from www.sciencedaily.com/releases/2008/05/080528095657.htm
Physikalisch-Technische Bundesanstalt. "Spectral Emissivity Measurements For Radiation Thermometry." ScienceDaily. www.sciencedaily.com/releases/2008/05/080528095657.htm (accessed November 26, 2014).

Share This


More From ScienceDaily



More Matter & Energy News

Wednesday, November 26, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Who Will Failed Nuclear Talks Hurt Most?

Who Will Failed Nuclear Talks Hurt Most?

Reuters - Business Video Online (Nov. 25, 2014) With no immediate prospect of sanctions relief for Iran, and no solid progress in negotiations with the West over the country's nuclear programme, Ciara Lee asks why talks have still not produced results and what a resolution would mean for both parties. Video provided by Reuters
Powered by NewsLook.com
Flying Enthusiast Converts Real-Life Aircraft Cockpit Into Simulator

Flying Enthusiast Converts Real-Life Aircraft Cockpit Into Simulator

Reuters - Innovations Video Online (Nov. 25, 2014) A virtual flying enthusiast converts parts of a written-off Airbus aircraft into a working flight simulator in his northern Slovenian home. Jim Drury reports. Video provided by Reuters
Powered by NewsLook.com
Car Park Solution for Flexible Green Energy

Car Park Solution for Flexible Green Energy

Reuters - Innovations Video Online (Nov. 24, 2014) A British solar power start-up says that by covering millions of existing car park spaces around the UK with flexible solar panels, the country's power problems could be solved. Suzannah Butcher reports. Video provided by Reuters
Powered by NewsLook.com
Microsoft Adds Robot Guards, Ushers In Sci-Fi Apocalypse

Microsoft Adds Robot Guards, Ushers In Sci-Fi Apocalypse

Newsy (Nov. 23, 2014) Microsoft has robotic security guards working at its Silicon Valley Campus. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:

Strange & Offbeat Stories


Space & Time

Matter & Energy

Computers & Math

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins