Re: [opensuse] [OT] How much power does a PC really consume?
Neil wrote:
On 2/18/08, Aaron Kulkis <akulkis00@hotpop.com> wrote:
James Knott wrote:
Ummm... He was talking about RMS, which implies voltage or current. There's no such thing as RMS power. RMS is short for Root-mean-squared i.e. _______ / 2 V X
Sqare root (x^2) is only a way of getting the absolute version of x. To get the actual RMS (normally used version) value of that you'd have to average that over a full cycle.
That's why there was a bar "_" over the X. It was there, ... someone's reply seems to have removed it.
RMS can apply to any function vs. time (voltage, current, power, etc.)
RMS is just as statistical method, which is useful for making sense of any time-variant function.
The square root of the square of power is just as much related to power as the square root of the square of voltage is related to voltage (NOT power).
I learned RMS was the exact calculation of the energy transmitted over a waveform and could be seen as the average of the sinus after rectification. The original measurement was measuring the heat of a resistor, and therefore the power flowing through it. I could be wrong (actually I'm quite good at that).
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On 2/18/08, Aaron Kulkis <akulkis00@hotpop.com> wrote:
Neil wrote:
On 2/18/08, Aaron Kulkis <akulkis00@hotpop.com> wrote:
James Knott wrote:
Ummm... He was talking about RMS, which implies voltage or current. There's no such thing as RMS power. RMS is short for Root-mean-squared i.e. _______ /_2 V X
Sqare root (x^2) is only a way of getting the absolute version of x. To get the actual RMS (normally used version) value of that you'd have to average that over a full cycle.
That's why there was a bar "_" over the X.
It was there, ... someone's reply seems to have removed it.
Sorry, I did. It fell off when I fixed the shifts that apeared when copying. Fixed it again. I seem to have forgotten what the bar meant. I knew it when I needed it for a test, but I lost it. Is it the arithmic mean? The arithmic mean is a way of averaging, if wikipedia (http://en.wikipedia.org/wiki/Arithmetic_mean) is correct. The average of a sine (if N cycles are taken) is 0. If the arithmic mean of a sine is plotted over a time period the result would be the exact same sine. The result of this would be that RMS is a useless value. It is not, and therefore my reasoning must be flawed somewhere. Does anyone have the time, knowledge and will to take the quest of finding this flaw? I seem to be unable to.
RMS can apply to any function vs. time (voltage, current, power, etc.)
RMS is just as statistical method, which is useful for making sense of any time-variant function.
The square root of the square of power is just as much related to power as the square root of the square of voltage is related to voltage (NOT power).
I learned RMS was the exact calculation of the energy transmitted over a waveform and could be seen as the average of the sinus after rectification. The original measurement was measuring the heat of a resistor, and therefore the power flowing through it. I could be wrong (actually I'm quite good at that).
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Neil wrote:
On 2/18/08, Aaron Kulkis <akulkis00@hotpop.com> wrote:
Neil wrote:
On 2/18/08, Aaron Kulkis <akulkis00@hotpop.com> wrote:
James Knott wrote:
> Ummm... He was talking about RMS, which implies voltage or current. > There's no such thing as RMS power. > RMS is short for Root-mean-squared i.e. _______ /_2 V X
Sqare root (x^2) is only a way of getting the absolute version of x. To get the actual RMS (normally used version) value of that you'd have to average that over a full cycle.
That's why there was a bar "_" over the X.
It was there, ... someone's reply seems to have removed it.
Sorry, I did. It fell off when I fixed the shifts that apeared when copying. Fixed it again. I seem to have forgotten what the bar meant. I knew it when I needed it for a test, but I lost it. Is it the arithmic mean? The arithmic mean is a way of averaging, if wikipedia (http://en.wikipedia.org/wiki/Arithmetic_mean) is correct. The average of a sine (if N cycles are taken) is 0. If the arithmic mean of a sine is plotted over a time period the result would be the exact same sine. The result of this would be that RMS is a useless value. It is not, and therefore my reasoning must be flawed somewhere. Does anyone have the time, knowledge and will to take the quest of finding this flaw? I seem to be unable to.
RMS can apply to any function vs. time (voltage, current, power, etc.)
RMS is just as statistical method, which is useful for making sense of any time-variant function.
The square root of the square of power is just as much related to power as the square root of the square of voltage is related to voltage (NOT power).
I learned RMS was the exact calculation of the energy transmitted over a waveform and could be seen as the average of the sinus after rectification. The original measurement was measuring the heat of a resistor, and therefore the power flowing through it. I could be wrong (actually I'm quite good at that).
-- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org For additional commands, e-mail: opensuse+help@opensuse.org
In practical electronics, true RMS is only needed to calculate the value needed to smooth rectified voltage from a source other than 50/60 Hz or the average power out of an audio amp into a speaker. Watts as in power supplies are simply volts times amps (E*I), the safe wattage for a resistor ie. to stop it turning into a toaster, is amps squared time resistance. Dave -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org For additional commands, e-mail: opensuse+help@opensuse.org
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 The Monday 2008-02-18 at 11:01 +0100, Neil wrote:
I seem to have forgotten what the bar meant. I knew it when I needed it for a test, but I lost it. Is it the arithmic mean? The arithmic mean is a way of averaging, if wikipedia (http://en.wikipedia.org/wiki/Arithmetic_mean) is correct. The average of a sine (if N cycles are taken) is 0.
But as in RMS it is squared first, it is always possitive.
If the arithmic mean of a sine is plotted over a time period the result would be the exact same sine.
The mean of the squares would be a flat line, at peak(squares) / root(2)
The result of this would be that RMS is a useless value. It is not, and therefore my reasoning must be flawed somewhere. Does anyone have the time, knowledge and will to take the quest of finding this flaw? I seem to be unable to.
Better here: http://en.wikipedia.org/wiki/Root_mean_square - -- Cheers, Carlos E. R. -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.4-svn0 (GNU/Linux) iD8DBQFHuW8vtTMYHG2NR9URApBQAJ9imFmAZQTNCtdM4DfCaqO57G2pWQCgmPFE hCMsXH+B5W0whdz4PFxtqV8= =Pf9E -----END PGP SIGNATURE----- -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org For additional commands, e-mail: opensuse+help@opensuse.org
On 2/18/08, Carlos E. R. <robin.listas@telefonica.net> wrote:
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1
The Monday 2008-02-18 at 11:01 +0100, Neil wrote:
I seem to have forgotten what the bar meant. I knew it when I needed it for a test, but I lost it. Is it the arithmic mean? The arithmic mean is a way of averaging, if wikipedia (http://en.wikipedia.org/wiki/Arithmetic_mean) is correct. The average of a sine (if N cycles are taken) is 0.
But as in RMS it is squared first, it is always possitive.
If the arithmic mean of a sine is plotted over a time period the result would be the exact same sine.
The mean of the squares would be a flat line, at peak(squares) / root(2)
The result of this would be that RMS is a useless value. It is not, and therefore my reasoning must be flawed somewhere. Does anyone have the time, knowledge and will to take the quest of finding this flaw? I seem to be unable to.
Better here:
Okay, here I can see: SQRT(MEAN(x^2)) (in pseudocode). The bar above the x in the original formula didn't show it was also above the ^2. Thanks. Neil
- -- Cheers, Carlos E. R.
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Neil wrote:
Sorry, I did. It fell off when I fixed the shifts that apeared when copying. Fixed it again. I seem to have forgotten what the bar meant. I knew it when I needed it for a test, but I lost it. Is it the arithmic mean? The arithmic mean is a way of averaging, if wikipedia (http://en.wikipedia.org/wiki/Arithmetic_mean) is correct. The average of a sine (if N cycles are taken) is 0. If the arithmic mean of a sine is plotted over a time period the result would be the exact same sine. The result of this would be that RMS is a useless value. It is not, and therefore my reasoning must be flawed somewhere. Does anyone have the time, knowledge and will to take the quest of finding this flaw? I seem to be unable to.
While the average of sin x over an an entire cycle is zero, it's not for sin^2 x, which of course never goes negative. -- Use OpenOffice.org <http://www.openoffice.org> -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org For additional commands, e-mail: opensuse+help@opensuse.org
participants (5)
-
Aaron Kulkis -
Carlos E. R. -
Dave Plater -
James Knott -
Neil