Message Board Thread - "temperature of a copper sample"

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temperature of a copper sample Marc L 2/16/2005
Hello,

I'm looking for feedback from IR experts out there on a temperature measurement on a copper sample, clean but not polished. This is located in a UHV chamber. A tiny (diam 3mm) highly energetic X-ray beam (200W/mm2) is directed on its surface where the temperature, according to simulations, should be in the range of 600C near the impact location. The sample is water cooled and hence the temp. gradient is sharp.
An emissivity of 0.3 was derived from pyrometer and thermocouple measurements while the sample was uniformely heated with resistors in the 200C range.
An initial test with a PtSi (band 3-5um) camera and sapphire window yielded results conform to expected values.
However, another test with a micro-bolometer (7-14um) camera and Zn-Se window gave significantly lower temperatures with a 0.3 emissivity.
Idea 1: the emissivity at lower wavelength is much lower --> A GaAs(3-5um)camera measurement was performed in the same conditions: still to low temperatures!
Idea 2: the Zn-Se window is attenuating a lot --> a value of 70% transmissivity was measured: not the explanation.
Idea 3: the line of sight is at a relatively shallow angle wrt the sample surface (40deg)--> we might not get all the flux: then why would initial test give good results?
Idea 4: the surface is cleaned/altered by the energetic beam and the optical caracteristic vary widely --> visual inspection reveal some brighter patches in heated areas.

Well, if you survived this rather long stuff, you're welcome to submit you thoughts ;-)

cheers
marc
 
Re:temperature of a copper sample raffar 2/17/2005
Items 1 and 4 are both likely.
You can see the emissivity of copper vs. wavelength on our site by going to http://www.pyrometry.com/emissivity.php#materials and scrolling down. As you'll note, different behavior is possible depending on sample, conditions, etc.
Also, the beam may very well be changing the emissivity, since surface morphology & chemistry play a big part in determination of emissivity.
 


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