Estimating internal (junction) temperature

AI Thread Summary
The discussion focuses on estimating internal junction temperature (Tj) in a motion sensor housed in a sealed metal enclosure. The user calibrates the device using an external temperature sensor but faces challenges during rapid temperature changes, particularly in the first five minutes after powering up. The significant temperature gradient between the case temperature (Tcase) and internal temperature (Tj) leads to inaccurate offset compensation. The user seeks a straightforward method to estimate Tj, assuming equal temperatures at startup. They also inquire about available online resources for further information on this topic.
Eli Hait
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Hello.

I use a kind of motion sensor located in a sealed metal enclosure.
I perform temperature offset calibrating to this device, using an external temperature sensor (attached to the enclosure). This solves the most of temperature problems except when the temperature gradient is large - for instance for 1'st 5 minutes afrer powering the device.
After checking this issue my conclusion was that in fast temperature gradients the temperature delta between the case temperature (Tcase, the one i measure) and internal (Tj) temperature is too large so i don't compensate the real offset error.

My question is if there is a simple method to estimate the internal temperature (Tj), if at the beginning (before powering up the sensor) the external and internal temperatures are equal Tcase=Tj.

Is there good information about it on the web?

Thanx,
Eli.
 
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