Interesting topic here guys - I've been saying "RMS power" since forever without giving it a second thought; it seems I may have been wrong!
To try and get a clarification on the original question (as I understand it, at least) am I correct in saying we are all agreed that "Average Power" and "RMS Power" are the same thing. Even if the nomenclature is not correct, these two terms *don't* represent different measurements that might produce different results when carried out on the same piece of equipment?
Hi,
Yes. RMS Power refers to the power when using RMS values to calculate it. This would differ from using peak values to calculate the power.
For example, if the RMS voltage is 10 volts and the RMS current is 1 amp, then the RMS power is 10*1=10 watts.
If we used peak values, then the peak voltage is 14.14v and the current is 1.414 amps which comes out to 20 peak watts, and if we used the RMS conversion factor of 0.7071 we would get 14.14 watts which would not be correct, but if we knew what we were doing we would realize that the two waveforms when multiplied together do NOT form a sine wave and so we can not use the conversion factor of 0.7071 (see below 'crest factor'), we must use the conversion factor of 0.5 instead. That would give us 10 watts too.
Another way of looking at it is that when we do a conversion using a simple constant factor like K=0.7071 we have to be aware of the wave shape, and that would be called the "Crest Factor". What we learned is that we can not blindly apply a crest factor to a problem WITHOUT knowing the wave shape. Obviously the crest factor for a squared sine is 0.5 and so we must use that factor instead to calculate the RMS power. Interestingly when we do take the time to observe the wave shape and correct crest factor, we do in fact get the right value which in the above example was 10 watts. So "RMS Watts" does in fact make sense, we just have to understand that when we use a short cut like the 0.7071 rule it is actually a crest factor and since that applies only to a sine wave we have to find the right factor for this new wave, which is a squared sine wave and therefore we must look up the correct crest factor for that wave instead and observe that we are calculating power not an actual RMS value.
So we have:
RMS Voltage=PeakVoltage*CrestFactor
RMS Current=PeakCurrent*CrestFactor
and lastly we have:
RMS Power=PeakPower*CrestFactor
so there is really no difference except we must have the right crest factor to fit the waveshape and application we are dealing with. The crest factor in this case may have to be called something else however such as the crest factor squared. Also, the actual crest factor may be 1/K as applied here.
And yes, RMS Power in this context means the same as Average Power and it looks like the standard at least in some places in the world was changed to read "Average Power" instead.