I am glad that we are slowly narrowing in on your misconception here. I hope the precise answers below help?
Quote from randombit0Mr Clarke ! You are mixing properties of the body and of the instrument calling that a definition of s property of the body!
No, I' never said band emissivity was a property only of the alumina - it is the definition of emissivity needed for thermography calculations with a sensor that defines the band... Of course it depends on the instrument!
Quote from randombit0
Are you writing your own science ?
This is a rhetorical flourish with no meaning? Which bit of science do you think I'm writing?
Quote from randombit0
Have you ever realized also that every pixel has his OWN B(V) ?
Now who is mixing things up? But I think you are confused. The bolometer sensitivity B(v) is the same for each pixel. What you mean is that the band (effective) emissivity eb(T) that you need to put in to the camera to get a temperature out can be varied pixel by pixel and this will (should) be in a case where eb depends on temperature. Note that v = optical frequency, completely different from T = surface temperature
Quote from randombit0
Calibration files serve just the purpose to eliminate the need to knowing the B(v) !
You never normally need to know B(v) because you calibrate eb(T) by measuring it, with the camera, at the operating temperature. That is Thermography 101 and what you are told to do in every thermography handbook. The authors here only did it at low temperatures (where they say they found errors in the book values), but used the "book emissivity value" for the high temperatures - not realising that book "total emissivity" is different from "band - or - measured by Optris" - emissivity.
Quote from randombit0
I think you are hopeless ! But try to read this page:en.wikipedia.org/wiki/Emissivity
You will read that the values are referred to Total Hemispherical Emissivity.
Correct (but I remain hopeful)
Quote from randombit0
And if you read the big amount of literature and Emissivity Tables available you will see that they all have very similar numbers even for alumina.
Correct. Because they are all giving total emissivity. Some of these tables actually say it is total emissivity. Some do not bother to say it and just call it emissivity.
Quote from randombit0so there is NOT a detector dependency on the numbers and nowhere is written "use this numbers ONLY with model XXX" !
That is correct, because no-one expects thermographers to use book emissivity values. It is as you point out not in general possible because the value you would need varies over the IR spectrum and depends on the camera. And it is contrary to what all the thermography manuals tell you to do.
You will find that nowhere in the thermography literature does it tell anyone ever to use total emissivity (without a calibration check) to determine temperature of some surface. They do say you should use emissivity for this purpose - meaning of course emissivity as determined by the specific camera. They say you should always do this calibration at temperature. If you do, then there is no problem.
One more thing. When the surface is a grey body - which is mostly true - book total emissivity, and band emissivity, are the same. That is because there is no large spectral variation in emissivity. Alumina is a very specially bad case that breaks this. The Lugano testers were unlucky that they had the wrong material.
So - this is a subtle mistake. You need to understand quite a bit before you get to the bottom of it. You should thank Bob Higgins and GSVIT for understanding this issue - I merely did the calculations (and corrected one of Bob's incorrect assumptions where he did not follow through his ideas to their conclusion).
Last word - an industry help page:
http://www.infratec.co.uk/ther…pectral-thermography.html
QuoteEmissivity values of materials greatly vary throughout the infrared spectrum. Concentrating the thermographic measurements on spectral ranges with an explicitly high or low emissivity can lead to detection of special effects.
The effect here was very very special!