liuyonggen_1
Full Member level 4
when using "measure" demand avg and rms in hspice ,respectively, to simulate the current with many hamonics, what's difference between the two results?
thanks a lot!
thanks a lot!
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McShamrock said:The average means simply taking values, summing them, and then dividing the results by the number of total values you consider. Actually, this measure doesn't give any information about the size of values: if they are both positive and negative the average will be similar to zero! Therefore, if you are interested on size of values without regard for positive or negative, a different approach must be used. You can think of taking values, without considering their sign, and then doing the above mentioned average. That can be a kind of measure, but actually it is not the best in terms of statistics. In statistical terms, the mean is done by squaring the considered values, and then by squaring root the average (the above mentioned one) of them.
The average is better called "arithmetic mean", the rms is called "quadratic mean" instead. Their is a relationship between those kind of measures, i.e. QUADRATIC MEAN^2 = ARITHMETIC MEAN^2 + VARIANCE, where VARIANCE is the variance of that particular population of considered values.
thank you very much!
i have another question, when i would like to calculate the power (a constant voltage times a current with many harmonic frequencies), should i use "rms".
that's to say,how to include the power of harmonic frequencies of the non-ideal current.
thanks a lot!
Kral said:liuyonggen_1,
An RMS voltage, when connected to a resistive load will produce the same amount of power as A DC voltage of the same value.
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Consider a square wave with a 1V "peak" value, a 0V "valley" value, and a 0.5 (50%) duty cycle. The average value is 0.5. The RMS value is 1/SQRT(2). The power dissipated in a 1 Ohm load = [Pveak^2/R] X Duty Cycle = [1^2/1] X 0.5 = 0.5w. The power generated by the [1/sqrt(2)]RMS Voltage = Vrms^2/R = [1/SQRT(2)^2]/R = .5/1 = 0.5 (Same answer).
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The RMS value of a voltage consisting of multiple frequencies (not necessarily harmonics) is equal to the Square root of (the sum of squares of the RMS values of each frequency).
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You can get the frequency components using a spectrum analyzer, or by doing an FFT of the waveform.
Regards,
Kral
sengyee88 said:RMS= 1/sqrt(2) is only valid for pure sinusoidal.
RMS of a square wave is actually equals to the mid point of the square pulse.