Imagine you want to measure the temperature of an electronic circuit and use an IR camera to take an image.
Some cameras don't take into account the emissivity of different materials or surfaces, so the temperature map has an error.
What is the magnitude of this error in comparison with the maximum temperature value? Can the influence of the emissivity be neglected? If yes, under which conditions?
Thank you in advance for your help!
I am terrified to say considerable difference may arise as per https://www.optotherm.com/emiss-effects.htm
Indeed... the contents of this page is very pragmatic! This means that the first thing to know is to determine the emissivity of the different elements / materials. Only then I'll have an idea about the measurement error.
I used to take into consideration emissivity when measuring the temperature of different metallic filaments, but in this case it was an easy task, I just had to give the emissivity value of the metal as an input to the optical pyrometer and the measured temperature was quite accurate.
Now if want to use an IR camera to measure the temperature of different elements on a circuit board things are not as simple...
Typing error led to terror :-)
It appears anything having less than 0.6 emissivity should not be measured by IR camera for temperature.
https://www.fluke.com/en/learn/best-practices/measurement-basics/thermography/how-emissivity-affects-thermal-images
Most metals, especially the polished ones are not for IR cameras!!!
https://www.instrumart.com/pages/209/metals-emissivity-table
The table shows electrical terminal blocks have 0.6 value. I am not sure if that helps....
If I'm understanding correctly, the issue you are facing is that in your IR camera image you have few different materials (which will have different emissivity values), but in your IR camera setting you have option to input only one emissivity value. I have seen IR camera where a small region can be selected, and the user can input emissivity for that small region. In this way the measured temperature is accurate. If this option is not available, then I can suggest this. Say you have 5 different materials in the image and you know the 5 different emissivity values. Now take 5 different images with these 5 emissivity values. In this way you'll get the temperature of the 5 different materials accurately. Only, you will not get one correct IR image (radiometric image) with temperature map. One nuance to this approach is that the material directly under the IR camera will give more accurate result compared to components which are in an angle with the camera.
In a broad sense, the relative error in temperature measurement due to incorrect value of emissivity will depend two things: (1). the variation of emissivity value, (2) the temperature range. Since you mentioned electronic circuit, in there, the shiny parts can have very low emissivity (less than 0.5). While some other components, say something painted with black paint can have emissivity > 0.9. So, depending on your emissivity range the IR camera temperature will vary. You can quantify the temperature error by varying the emissivity. You'll see as you increase emissivity, the IR camera temperature decreases and vice versa.
I remember that, the heat flux sensed by the IR camera is proportional to the emissivity times the temperature power 4. So, I think at higher temperature, your temperature reading error due to incorrect emissivity will be lower.
Hi Farhan Rahman , thanks for the detailed reply. I guess that taking photos with the different emissivity values is the best way to go in my case.
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