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https://designers-guide.org/forum/YaBB.pl Measurements >> Other Measurements >> Average Power Vs. RMS power https://designers-guide.org/forum/YaBB.pl?num=1103785899 Message started by crhu on Dec 22nd, 2004, 11:11pm |
Title: Average Power Vs. RMS power Post by crhu on Dec 22nd, 2004, 11:11pm Hi, forum, I am wondering what is the criteria to use average power or RMS power in power simulation. Acordingt to Poynting's theorem, Sav=Re(EXH), average power should be enough for power measurement all the EM field. However, I find that there are many places, esp. in RF ckt, RMS power is used instead. Any inputs are highly appreciated. Thanks. --crhu |
Title: Re: Average Power Vs. RMS power Post by Ken Kundert on Dec 27th, 2004, 1:13pm Charlie, Average and RMS power are the same, are they not? The equation you gave for Poynting's theorem assumed the use of phasors, which assumes sinusoidal signals. When using RMS you are allowing signals other than sinusoids to be used. -Ken |
Title: Re: Average Power Vs. RMS power Post by crhu on Dec 27th, 2004, 5:58pm Hi, forum, I googled "RMS average power" and here is something giving me some hints: http://www.dartmouth.edu/~sullivan/techniques.pdf "More generally only components of v(t) and i(t) at the same frequency contribute to average power" If it is true ( I do not know how to derive it yet), average power can not characterize the power for non-linear circuit. Am I right? Thanks. --Charlie |
Title: Re: Average Power Vs. RMS power Post by crhu on Dec 28th, 2004, 2:02pm Hi, Ken, I went through the Poyting's Therom one more time, and you are right that the Saverage = Re(SXconjugate(H)) is in the format of phasor. As any periodic inputs can be decomposed into sinusoids of different frequency, the Therom should be able to apply to all the periodic/quasi- periodic inputs. I do think right now that there is a hidden assumption in Poynting's Therom: the changing E field only generates the M field with the same frequency; so does the changing M field, as the linear, homogeous medium is assumed. So, seems to me that the average power is not a good enough measurement for a non-linear system. Thanks. --Charlie |
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