[ltp] X61 power consumption

[Leszek Koltunski]

> 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.

I just talked to hardware engineers in my company and they say the same - 
thermal imaging would probably not suffice if we wanted to estimate how 
much power is a given chip drawing. Shows what I know.

However, we do not need to presisely measure that; we only need to 
identify which parts draw more power under Linux than they do under 
Windows. So I hope one can just image the board running Windows and 
then running Linux, and compare... Then again, I am a software engineer :)