Author Topic: Temperature accuracy with auxiliary close-up lens  (Read 1184 times)

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Offline JohnGTopic starter

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Temperature accuracy with auxiliary close-up lens
« on: April 14, 2017, 05:01:04 pm »
Folks,

I have a question about the use of auxiliary lenses for close-up temperature measurements. The application is the measurement of die temperatures of GaN power FETs, and the smallest transistors of interest are about 0.9 mm x 0.9 mm. In the ideal case, I'd want at least 9 pixels on the FET.

If I use an auxiliary lens to get close-up measurement capability, how might this affect the accuracy of the temperature measurement, i.e. how much might the absolute temperature accuracy be degraded?

Thanks,
John
"Reality is that which, when you quit believing in it, doesn't go away." Philip K. Dick (RIP).
 

Online Bill W

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Re: Temperature accuracy with auxiliary close-up lens
« Reply #1 on: April 14, 2017, 08:02:26 pm »
The simple answer is quite a bit.  However you can easily 'recalibrate' the camera and generate a lookup table from 'camera reading' back to 'real reading'.

Ambient will still be ambient.
You will have changed the 'gain' and cameras are linear in thermal radiance difference - not temperature difference.  At a guess you are looking at over 100°C so this begins to matter.  A bit of maths (there's a couple of spreadsheets somewhere on the forum already) will sort this out.

So a few measurements of known hot temperature 'black' bodies through your new close-up optics set will give you the scaling.  You may get some centre to edge shading, so stick to calibrating the centre.

regards
Bill


Offline JohnGTopic starter

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Re: Temperature accuracy with auxiliary close-up lens
« Reply #2 on: April 15, 2017, 02:42:11 pm »
Thanks, Bill.

Looks like it is doable, but I will have to review the math. I have to do it for lenses, anyway...

John
"Reality is that which, when you quit believing in it, doesn't go away." Philip K. Dick (RIP).
 


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