I have started this thread to provide a home for the Optris posts, which are derailing RossiVDarden2. Apologies in advance if I missed one, or move one too many (for some). Alan
Not quite the right thread, but it will do.
How to check emissivity calculations
Wyttenbach has for a long time promoted the idea that Optris engineers have told him that the camera software incorporates emissivity e into temp measurements as:
T = T0/e^(1/3)
T is the camera calculated temperature for emissivity = e where T0 is the camera calculated temperature for emissivity = 1.
So that T scales as exponent 3 of 1/e independent of T.
Rossele, Levi and others have promoted the idea that total emissivity must be used in these calculations and hence exponent = 4 uniformly of temperature (see below).
As opposed to what the camera must do to be accurate, which is to vary the exponent smoothly with T according to the Planck function evaluated over the Optris sensor passband. We expect an increasingly higher exponent at lower temperatures as the passband gets higher in frequency relative to the Planck peak. At very high temperatures the IR passband occupies the RayleighJeans part of the Planck curve  much lower in frequency than the peak  where the exponent is 1. For the Lugano test higher temperatures in the active test we had approximately an exponent of 2. An exponent of 4 would be what Levi would I guess expect since he claims that total emissivity is the only relevant parameter. We know that this scales at T^4 because total radiation scales like this.
So let’s do some limited checking, courtesy MFMP:
(1) Download the Optris PI Connect software and a sample camera ravi file from MFMP dogbone 2 thermal assessment experiment.
(2) view the ravi file  note that segment AL with defined emissivity 0.95 temperature 59.7C in the layout (go to tools>configuration to see this).
(3) change the layout emissivity for AL area from the tools>configuration screen from 0.95 to 0.475 (1/2 of old value) and save
(4) Note the changed temperature for AL
(5) repeat to get Optris calculated temperatures for a range of emissivities.
I've tabulated some values below, and the calculations I use to work out the corresponding exponent (the site here imports cut and pasted excel spreadsheets nicely, which is great)
e 
eratio 
T/C 
T/K 
Tratio 
exponent  
0.99 
1.1 
58.4 
331.4 
1.009656005 
9.918139261 

0.9 
61.6 
334.6 



0.55 
1.1 
82 
355 
1.013802817 
6.952671482 

0.5 
86.9 
359.9 





0.22 
1.1 
142.9 
415.9 
1.020678048 
4.656737156 

0.2 
151.5 
424.5 





0.165 
1.1 
170.4 
443.4 
1.02277853 
4.231687462 

0.15 
180.5 
453.5 



0.11 
1.1 
218.1 
491.1 
1.026471187 
3.64797291 

0.1 
231.1 
504.1 
I don't easily have a way to generate additional Optris camera ravi files so cannot in this way test higher temps: 0.1 is an emissivity limit in the software. If someone can unearth and post some of these (Paradigmnoia?), we could see precisely how the Optris camera responds over the entire temperature range, and check further.
Of course, TC's paper has done this theoretically, assuming the Optris camera software works correctly. MFMP have confirmed it experimentally. But it seems some here: specifically ele and Wyttenbach will be more convinced by their own checks than what other people say? Perhaps this would help Levi, too?
After all, were total emissivity to be the relevant parameter as Levi says we would need to integrate radiance over all frequencies and therefore have an exponent uniformly of 4 regardless of temperature. And were Wyttenbach to have correctly understood the Optris support guy he spoke to we would have exponent uniformly 3.
I needed to check this since I could not otherwise be certain that Optris were not selling camera software that just did not work for greybodies, though this is a bit unlikely!
Wyttenbach  please contact your Optris support person who told you the exponent was always 3 and set them right  giving this simple check that anyone with a PC and web access can make.
It is perhaps interesting from these figures that at a temperature around that used in the Lugano dummy test we have exponent=4 consistent with what Levi thinks!