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zaki
, Joined ,

zaki

,
Joined

09:19 Nov-27-2002
IR Thermography


Just for curiosity..

In Thermography method, measurement appear in Temperature (oC), but theoritically the measurement is performed in term od total receiving radiation power (W). Is there any relationship between temperature vs. radiation..



 
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Alberto Monici
Engineering, Leak Detection Service - Thermography Service -
ETS Sistemi Industriali, Italy, Joined Aug 2002, 17

Alberto Monici

Engineering, Leak Detection Service - Thermography Service -
ETS Sistemi Industriali,
Italy,
Joined Aug 2002
17
09:55 Nov-27-2002
Re: IR Thermography
Dear Mr.Zaki
For a black-body the relationship is that gived by Plank's law, in wich:
W= (2*pi*h*c^2)/((lambda^5)(e^(hc/lambdakT)-1))
in which W is the spectral emissivity [Watt/m^2*meter] and T is the black-body temperature in Kelvin.
The intergal of the Plack formula in all the lambda possible give the Total Energy Emission (Stefan-Boltzmann law):
Wt=k*T^4
where k is the Stefan-Boltzmann constant.
For a grey-Body (like that normally measured in nature), the emissivity of the body, its spectral transmittance and the spectral absorbing coefficient give a total emittance below then a black-body. So the formula is: Wt=E*k*T^4, where E is the ratio between emittance of grey and black bodies.
I Hope to be exhaustive for your couriosity. Don't exitate to contatct me for any other question.


:
: Just for curiosity..
.
: In Thermography method, measurement appear in Temperature (oC), but theoritically the measurement is performed in term od total receiving radiation power (W). Is there any relationship between temperature vs. radiation..
.



 
 Reply 
 
Robert Paynter
R & D,
U of Oxford, United Kingdom, Joined Jun 2001, 14

Robert Paynter

R & D,
U of Oxford,
United Kingdom,
Joined Jun 2001
14
01:33 Dec-02-2002
Re: IR Thermography
Alberto Monici wrote:
: Dear Mr.Zaki
: For a black-body the relationship is that gived by Plank's law ...

:: Just for curiosity..
:
: In Thermography method, measurement appear in Temperature (oC), but theoritically the measurement is performed in term od total receiving radiation power (W). Is there any relationship between temperature vs. radiation..
: .
.
Alberto Monici gave the total, but most sensors have a limited band of detection and you need to allow for that. CMT (Cadmium/Mercury/Telluride) is the favourite at typical ambient temperatures because it's response ends up being almost linear in this range. InSb (Indium Antimonide) can do these low temperatures but is much better (more linear) at higher (600K +).
They are well behaved responses so will be calibrate within the camera.

As a user you need to take care that the emission of your observed surfaces is taken into account - some are unexpectedly good with IR eg. white snow.

Robert


 
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