Message Board Thread - "Emissivity of an Arc "

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Emissivity of an Arc catlinj 4/12/2001
I use my pm595 to dtect discharges over and HV bushing. I by chance caught an arc on one of my images and would like to know what my emissivity setting would be to measure this arc?

Please reply to me on John.Catlin@Eskom.co.za
 
Emissivity / Arc Temperatures Bernie Lyon 1/8/2004
Arc temperatures can vary quite a bit, but the temperatures are extremely high. They would probably be outside the range of your PM595. An object hot enough to emit white light, like the sun, would have a temperature of about 5500 degrees Celsius. Arc welders can produce temperatures of 5000 degrees Celsius. After all, these arcs are hot enough to melt steel. The tungsten filament in an ordinary 100 Watt light bulb can reach temperatures of 2500 degrees Celsius. The current and length of the arc are also factors that contribute to the temperature. I would suspect that you are outside the range of the Spot-Size-Ratio of your camera, even if you used a 12 degree lens. Arcs are small targets, and you certainly would not want to get closer for better observation. As for the actual emissivity, I do not know. You might try looking at the spectral signatures of arc lamps to get some idea. Most of these do not look at all like blackbody radiation curves, but have noticeable spikes in various wavebands. Unfortunately, most of these spectral signatures are confined to the visible or near IR wavebands and not in the longwave region (8-12 micrometers) of the PM 595. Here is a site with some additional information:

http://www.madsci.org/posts/archives/feb2000/951233685.Ph.r.html
 


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