Quote:
Originally posted by Groth
What are people's thoughts on accuracy? Temperature resolution/accuracy, probe separation distance, thermal conductivity, non-uniformity of die heating, heat shadowing, . . . .
You're good with the numbers, Les. How will the errors propagate? Which factors warrant the most work?
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Regarding accuracy.
As far as the blocks dimensions go the outside dimensions are 7.8x14x12.1 mm. These are accurate to whatever I can get with my little mill's xyz slides and vise. Figure +/-0.05mm. I believe it is actually better than that, more like 0.02mm. The (1mm) hole spacing is 10mm, accurate to better than +/-0.04mm. Because it is a single movement with the X cross-slide I am confident that it is more like <0.01mm. However the location of the (0.5x1mm) probes
within the holes is uncertain, within +/-0.2mm is my estimate, so that is the accuracy that must be assumed. =+/-2%.
Temperature resolution is hard to say, with a lot of measurements to average it should be reasonable (0.1°C), accepting that the calibration method is valid. Accuracy is probably +/-0.1-ish, also dependent on acceptance of cal method, bearing in mind that absolute accuracy (ie relative to 0°C) is not the issue, rather linearity and compression/dilation (?) accuracy of the calibration reference, in this case an alcohol thermometer.
Non uniformity of die heat. No real idea, instinct says it's only significant for the thermistor closest to the CPU which only has 1mm to even itself out.
Heat shadowing. Also not sure. Something is dancing around my brain saying it's irrelevant but I can't qualify it yet. Something similar to the reason the TIM joint is also irrelevant. (Thinking... ...might need the hole all the way through to be true... maybe L needs an offset...)
Errors. My simplistic approach would be to do three calculations, one with measured values, one with worst case minimum and one with worst case maximum, and derive the end accuracy from that. That is not how statisticians do it though I am certain.
Cather, I am showing my ignorance here, what do you mean by "CPU disconnect"? Is this some way to force the CPU to full idle? I seem to remember some software (waterfall?) that did this.
I am calling "running no programs except Excel", Idle. Is there a more correct alternative to this?
pHaestus, seeing as I feel a bit responsible for this, I could make another one for you to try out. I would need to know the TC hole diameter and CPU type plus what hole spacing YOU feel comfortable with. If you can measure the temperatures accurately it would be advantageous to keep it as small as possible (5mm?), less secondary path loss. I haven't measured beyond stock voltages yet and already temps are getting pretty high.
Let me know if you're interested, I can do the data analysis if someone verifies it.
My data is
here in this directory.
OK, now to record some more data.
Cheers
Incoherent