RMS Power?

Hi Roger,

I haven't read any of the Wikipedia article besides the paragraph Kijanki quoted in his post, and I don't consider whatever flaws the article may have to be relevant to Kijanki's point about terminology, especially given the further explanations of his point that I have provided.

I provided a link to the article simply because you requested it, and I was able to find it quickly.

Regards,
-- Al 

@almarg 

To be sure it’s clear, I absolutely did not say that "RMS power" varies as a function of time, although I can see how my statement might have been misread. I said that...

... what the words "RMS power" literally mean is the RMS value of a waveform that defines how power varies as a function of time.

(The "waveform defines how power varies as a function of time"; the RMS value of that waveform of course does not define how power varies as a function of time).

The paragraph above appears to me contradictory. First you say the waveform defines how power varies as a function of time. That would be instaneous power or instaneous heating, agreed? The RMS also defines how power varies as a function of time and defines its DC heating value. We needed that when Tesla won the "war of the currents" over Edison. How else were we to specify the voltage of the required sine wave.

As to the WIckipedia article i did find it and its many flaws. If you have the time, rather than defend kijanki do some reading yourself. There are 18 complaints about this article on the talk page of which 13 and 14 pretty much kill the whole thing. If kijanki learned this from articles like this then he is in the same mistaken camp. Shall we leave him there?

Would you care to tell me why an amplifier producing 100 watts RMS is any different than an AC generator producing 100 watts RMS. We are talking about sine waves here, that is all. 
 
And then please where 141 watts comes from. What kind of inbetween power is that to be called?

@kijanki . FWIW some respected manufacturers quote power output as for example 200 watts RMS. I am with atmosphere - the term is used,usefully, in the trade, for amplifiers. This is not hard for you to verify. Interesting post thanks. 

That would be instaneous power or instaneous heating, agreed?

Yes.

The RMS ... defines its DC heating value.

Yes.

The RMS also defines how power varies as a function of time ...

Well, if the waveshape is known, for example if it is known to be a sine wave, then of course one can determine the amplitude of that waveform from the RMS value. But I don’t see how my statement that you were referring to is contradictory, as you claimed. My statement, once again, being as follows:

... what the words "RMS power" literally mean is the RMS value of a waveform that defines how power varies as a function of time.

Honestly, I think you may be misreading my statement.

Would you care to tell me why an amplifier producing 100 watts RMS is any different than an AC generator producing 100 watts RMS.

The 100 watts is the same in both cases, of course. I have never said anything that is in any way to the contrary, and as far as I can recall neither has Kijanki.

And then please where 141 watts comes from. What kind of inbetween power is that to be called?

As I have said, it is the RMS value of a sinusoidal power waveform having a peak value of 200 watts.

There are 18 complaints about this article on the talk page of which 13 and 14 pretty much kill the whole thing. If kijanki learned this from articles like this then he is in the same mistaken camp. Shall we leave him there?

The fact that the article has numerous flaws has nothing to do with the subject matter of this thread. And Kijanki is a very experienced engineer who doesn’t need any such help.


I have nothing further to say on this matter.


Regards,
-- Al

@almarg 

And then please where 141 watts comes from. What kind of inbetween power is that to be called?

As I have said, it is the RMS value of a sinusoidal power waveform having a peak value of 200 watts.

Well its not. We have agreed that a 100 watt RMS amplifier supplies 40 volts peak into an 8 ohm load. 40 x 40 / 8 = 200 last time i checked. 

As Monty Python says... say no more, say no more.