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Greetings... Waveforms Live and OpenScopeMZ have generally worked very well for me.

One small problem is the RMS calculation in the Math Menu.   It seems not to subtract off the mean value...

seems to be sqrt((1/(N-1)) (Sum (V^2))), should be sqrt((1/(N-1))(Sum((V-V_mean)^2)))...  

anyone else notice this?   I work around by outputting the .csv file and computing there.

Thanks for any help for feedback.

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Hi @HarryNNelson,

I have reached out to the engineer more familiar with the WaveFormsLive firmware about this, though I think you only subtract the mean when calculating standard deviation rather than RMS (or at least the Wikipedia page seems to confirm my memory on this:https://en.wikipedia.org/wiki/Root_mean_square )


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  • 4 weeks later...

Thanks, yup, that seems to be the documented way of doing it... the RMS when there is a significant non-zero mean isn't particularly useful though, particularly when the mean is rather larger than the standard deviation, since they add in quadrature.  The RMS just ends up being almost exactly equal to the mean.

The standard deviation is a lot more useful... quantifies noise, for example... ripple on a DC voltage source.

But I agree that the official RMS is what is given, that is consistent.  I'd suggest considering changing to the standard deviation.

all the best, Harry

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