freecell said:
there is no such thing as "RMS Power" and furthermore, The RMS value of power is not the "AVERAGE" (equivalent heating) power and in fact, it doesn’t represent any useful physical quantity. The RMS and average values of nearly all waveforms are different. A notable exception is a steady DC waveform (of constant value) for which the average, RMS, and peak values are all the same.
http://www.firecommunications.com/rmspwr.pdf
freecell, in the strictest sense there is no such thing as the RMS value of a Power signal, but rather RMS Power describes the metrics used in the calculations. The terms Average and RMS on the meters describe how the voltages or currents are calculated. Average meters rectify the signal and average the value which works OK for DC but does not work very well for AC. RMS meters are designed to read the RMS values of a sinusoid, and True RMS meters read the RMS value of any periodic waveform.
True Power, or Average Power, can only be calculated with RMS values of voltage and/or current when the signals are time varying and periodic. RMS by definition means that its value is exactly equivalent to a DCV or DCI source of the same value. This is a fact and these values are the only values that accurately represent Joules/Second => Power...
RMS will always be asscociated with True/Average power since any other method of determining the power will give the wrong results. So that is why your hear RMS Power, plain and simple.
Here is the relationship between Average Power (Pavg) and PEP, I thought I would show the relationship between these two measurements as they relate to an AM signal that is modulated between 0% to 100% with a single tone.
The modulation index (m) is the ratio of the modulation voltage (Vm) to the carrier voltage (Vc) and this value should really never exceed 1 or the output signal will be distorted.
m = Vm / Vc
However, most people use an o'scope to view the output waveform and the modulation index can be calculated from this waveform. The maximum positive peak of the envelope is measured (Vmax) and the minimum positive peak of the envelope is measured (Vmin) and these values can be used to find m. When Vmin contacts the zero voltage level, 100% modulation is achieved.
m = (Vmax - Vmin) / (Vmax + Vmin)
Once this value is known, along with the dead key or carrier power (Pc), PEP and Pavg can be determined.
PEP = Pc x (1 + m)^2
Pavg = Pc x (1 + (m^2)/2)
Now if these equations are set up as a ratio, then the following relationships exist:
Pavg = PEP x (1 + (m^2)/2) / (1 + m)^2
PEP = Pavg x (1 + m)^2 / (1 + (m^2)/2)
So, a 100% modulated 4W carrier will produce a 16W PEP signal that is actually 6W Average and both values are based on RMS values.
