when analyzing the waveforms, right clicking while holding the CTRL key brings up a number of calculations to perform on the waveform such as max, min, avg, rms, AC rms, etc. What is the difference between AC RMS and RMS? I have a simple RLC circuit, and the power across the resistor is the between RMS and AC RMS, but it is different for the power calculations(?)?
The calculations for the power dissipated in the resistor also don’t add up to me. The Irms = .00444, Vrms across the resistor, V(n02) = .0444, so I’m expecting the power to be 0.4444*.004444 = 197uW. But, P(R1) as calculated by Qspice is ~= 242uW. *** NEVER MIND, Vrms*Irms = average power!!! ******
But, back to RMS and AC RMS, the AC RMS and RMS calculations are the same for currents and voltages, and Power for the source, but are different for the power dissipated in the resistor -why is that in a purely AC circuit?
Ivan, thank you for your response. I get it, in this case, it is separating the AC component of the rms from the DC – this makes sense. But in the updated post above, for this AC circuit, the AC RMS power and the RMS power in the resistor are different -why is that?
When you look at the power of R1, you can see that the waveform has dc offset (It is oscilating from 0 - 400 uW) and that is why you have difference between ac rms and rms.
You slipped and went for rms of the power, which doesn’t make much sense. Generally people think it wise to make the user interface “orthogonal” as they say – offer a consistent set of operations to apply to any plotted value – whether the programmer can for foresee a sensible use for the resulting combinations or not.
