On 31/01/2017 23:03, rickman wrote:
> There would appear to be something wrong with your numbers.  If you
> raise the ambient temperature 1 degree, the core of the CPU should rise
> 1 degree.  If you lower the ambient temperature 1 degree, the core of
> the CPU should lower 1 degree.

Only if there is a perfect heat transfer between the chip's core and the
surrounding environment.

> Your first example is close enough it can be chalked up to measurement
> uncertainty (electronic thermometers are not very accurate).  The second
> example is hard to explain.  I suppose there could be some effect from
> the air being dryer at temps below freezing and so not being as
> effective at carrying away the heat.

I suspect its the difference between the active cooling in the fridge,
and the passive cooling inside the car. The Pi had no heatsink and was
in a case, albeit one with quite a lot of ventilation, but probably
enough to retain some heat. All the other temperature sensors were some
distance away from the case.

What I'll do if I try it again, is to put one of the probes inside the
case to see how the chip, ambient and case temperatures are related.

---druck



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