[ltp] X61 power consumption

[James Knott]

Leszek Koltunski wrote:
>
>
>> That would be rather difficult, as in order to measure the power, you
>> have to measure current and that means cutting the power connection to
>> the chip, to insert the meter in series.  Now if you wish to volunteer
>> your ThinkPad to be butchered...
>
> Oh, come on, I am not an electrical engineer, but I am sure it's
> possible to do that in a non-invasive way, for example doing precise
> thermal imaging of the mainboard.
>
> It seems to me such hardware-level measurements would be very
> enlightening...
Well, I did study electrical engineering and have many years of hands on
experience repairing computer boards (from mini computers) among many
other items and I've never heard of such a thing.  You can certainly
determine relative temperatures, but actual power disapation depends on
a lot of other things.  For example, two devices could be consuming the
same amount of power, but one may have lower temperature because it's
cooled better or is passing some of that power onto another device or
the hotter device may be sinking power from some other device etc.  The
only way to reliably measure the power consumed by individual chips is
to measure the current and voltage and multiply them, to calculate
power.  Direct reading watt meters do just that.  Measuring voltage is
easy.  Measuring current means opening the circuit to measure current or
using some device that can measure the magnetic field caused by the
current and then applying some math to calculate current.  Bottom line,
you can't just take a picture and say this device uses this much power. 
Don't forget,  simply by taking the circuit board out of the case so you
can take that picture will affect the thermal flow from all the devices,
simply due to the change in cooling.


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