RMS Power?


I often see power specifications like "100W RMS".  There is no such thing as RMS power.  Of course, you can calculate RMS value from any curve, including power curve, but it won't represent anything.  "Real" power representing heat dissipated in resistive load is "Average Power"   Pavg=Vrms*Irms.   In case of sinewaves Pavg=0.707Vpeak * 0.707Ipeak = 0.5Ppeak,  or Ppeak = 2Pavg. 

Term "RMS Power" or "watts RMS" is a mistake, very common in audio.
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Showing 3 responses by imhififan

Faulty term watts rms or rms power came most likely from around 1975 FTC standard for power rating. FTC realized, that they goofed up and 25 years later in 2000 they corrected it .
http://www.n4lcd.com/RMS.pdf
I think Roy Lewallen explained it very well:
http://eznec.com/Amateur/RMS_Power.pdf
In his summary:
The equivalent heating power of a waveform is the average power.
The RMS power is different than the average power, and therefore isn’t the equivalent heating power. In fact, the RMS value of the power doesn’t represent anything useful.
The RMS values of voltage and current are useful because they can be used to calculate the average power.