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Unread 11-25-2005, 07:12 AM   #305
Cooling Savant
Join Date: Sep 2003
Location: Vallentuna, Sweden
Posts: 410

Originally Posted by RoboTech
. The temperature probe is mounted into a tiny hole drilled into the bottom of the copper heat spreader and is potted with thermal epoxy. The temp probe lead wires exit thru a hole drilled up thru the center of the heat die. This places the temp probe ~0.5mm from the top surface and eliminates the variability’s caused by the TIM joint.

Originally Posted by unregistered
...would set the sensors differently ...

Lee, I like this arrangement for many reasons but there is one problem with the vertical hole for the temperature sensor that I think is insurmountable.

Basically it means that there is a large uncertainty in the vertical location of the point that is measured which makes it impossible to use the data for any kind of modelling. The vertical shaft will have a different temperature gradient than the copper around it and the position of the sensor is uncertain.
Compare this to a horizontal hole. The gradient (in the vertical direction ) is the same as the surrounding copper, the measured temperature is some kind of average of the temperature of the hole surfaces and does not vary by more than a tiny amount along the length of the hole. In the case of the vertical shaft the same applies, namely that the measured temperature is some kind of average of the shaft surfaces, except that the temperature is varying hugely along these surfaces and a small "position error" would have a large impact on the measured temperature.

Edit: I have drawn something to try and explain explain this, I believe it is very important that you don't do this. The holes should be horizontal. Always. Their effects (heat shadowing) can be modelled, the effects in a vertical shaft can't.
Attached Images
File Type: gif tc_errors_from_pos.gif (16.4 KB, 17 views)

Last edited by Incoherent; 11-25-2005 at 07:32 AM.
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