Message-ID: <003001c0c133$be14c920$f208e289@mpaul> From: "Matthias Paul" To: References: <01FD6EC775C6D4119CDF0090273F74A4022027 AT emwatent02 DOT meters DOT com DOT au> Subject: Re: Power measurement Date: Mon, 9 Apr 2001 19:52:17 +0200 Organization: Rechenzentrum RWTH Aachen MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 5.50.4522.1200 X-MIMEOLE: Produced By Microsoft MimeOLE V5.50.4522.1200 Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from quoted-printable to 8bit by delorie.com id QAA14134 Reply-To: opendos AT delorie DOT com 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 ------------------------------------------------------------ Matthias Paul, Ubierstrasse 28, D-50321 Bruehl, Germany http://www.uni-bonn.de/~uzs180/mpdokeng.html ------------------------------------------------------------ My homepage has moved, please update your pointers.