Mail Archives: opendos/2001/04/09/16:30:09
On 2001-04-09, Joe da Silva wrote:
>Wow! For an O/T, this stuff about SI/Imperial/American
>terminology and measurements sure generated a lot of messages!
I value off-topic threads from time to time, because they can help
to create a more familiar atmosphere. However, I wished we
would have at least a similar amount of truely DR-DOS
related posts at the same time... It seems, there is little left
to say on DR-DOS until Lineo will eventually make up their
mind... Maybe thereīs something we can do to help them
making a good decision? ;-)
>If you measure the RMS current and multiply by the (RMS) voltage,
>what you have is the "apparent power" (VA), not the "real power"
>(W). That's the reason why the "power" figures quoted below are
>higher than expected. Now, "apparent power" (VA) is the _vector_
>sum of "real power" (W) and "reactive power" (VAR).
>
> [omitted much important stuff for shortage here]
>
>So, the only way to correctly measure the power consumption of
>PC equipment, is to either use a proper power meter (hard to find)
>or use an energy meter (eg. the one at the front or side of your
>house) and see how much energy it accumulates in one hour (if
>necessary, run the test for several hours, then divide the energy
>accumulated, by the number of hours).
Yep, all you write is correct - I didnīt go into all the physical
details because I considered this would be even more off-topic
and I would have had difficulties to explain this in English,
anyway (but itīs good to know the English terms for it now ;-).
The power providers have a strong interest in keeping the
reactive power portion (Imaginäranteil) low to reduce their
losses and it is an issue for some of these "logo programmes",
you usually find on the label of a device. Thatīs why many
electrical devices have some capacitors and/or coils near the
power inlets. Modern quality power switching supplies often
have "active power correction" so that they "look" more like
a resistive load (Ohmsche Last) to the power provider. However,
you are correct, it must be taken into account for accurate results.
I only wonder why power meters are so hard to find, as you mention.
At least over here you can lean them (for free or for a minimal
fee) from any power provider. More simple power meters in
form of plug adapters with integrated electronics and LC display
are also available in most electronics shops for about 25 - 75
USD depending on accuracy and features (f.e. measuring over
a longer duration of time and calculating average and peak
values). They should have circuits to compensate for the effects
you mentioned.
BTW. I used one of them when measuring the power consumption
of that monitor, but I guess 37 W is still an exception at the
upper limit.
But anyway, itīs not the single device that becomes a problem,
itīs the thousands and millions of similar devices that we tend
to plug in once and forget, and that waste energy without doing
anything most of the time (except for producing some heat... ;-)
Bernie mentioned that we Germans could shutdown one or two
of our nuclear power plants if this standby load could be
significantly reduced. This is in fact so, although this does not
only apply to Germany but to almost all countries...
Well, itīs a slow and sometimes difficult process to bring this
to Mr./Mrs. Averageīs attention, because people tend to give
up all too easily if they donīt see any immediate results...
Greetings,
Matthias
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Matthias Paul, Ubierstrasse 28, D-50321 Bruehl, Germany
<Matthias DOT Paul AT post DOT rwth-aachen DOT de> <mpaul AT drdos DOT org>
http://www.uni-bonn.de/~uzs180/mpdokeng.html
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