How do I calculate the RMS overall of a linear spectrum?

[rwbrook@integratedps.com]

this is a post data capture calculation, so it should be no big deal, but I can't get it right.  I have a 16,250 line linear spectrum.  I want the RMS overall for that spectrum.  That means, take each y value for each point and square it.  Add up all those squared point values and then take the square root of the summation.  THAT is the RMS overall of that spectrum.  There are ways to do it in time galore.  I am assuming I need to do it with a point to  point vi and the formula node.

Regards,

Ron

[.aCe.]

If you have the full development system, just use http://zone.ni.com/reference/en-XX/help/371361K-01/gmath/rms/#parent

If not try this:

[Julien_31]

Hello,

I don't really understand why you see it so complicated. ^^

Here are 2 different ways to calculate your RMS value :

Is it what you need to do ?

[crossrulz]

The RMS.vi is found in the Mathematics->Probability & Statistics palette.  Makes life a lot easier on you.

[rwbrook@integratedps.com · Accepted solution]

Thank you.  I wanted to try that vi but could not find it.

Regards,

Ron

[rwbrook@integratedps.com]

Gentlemen,

Same issue, different slant.  If I have already calculated the RMS overall for a time domain waveform, it is correct to multiply that overall value by 25.4 to change it to a metric reading?  Is it correct to multiply it by 0.707 to change that overall value to an RMS overall?

Regards,

Ron

[Julien_31]

Umax = 1.414 * Urms is true only for "perfect" sinus signals...That's just an approximation. And the mathematical definition if RMS is as follow :

http://en.wikipedia.org/wiki/Root_mean_square

[rwbrook@integratedps.com]

Yes, but if you consider the original RMS calulation was performed by treating every invidual frequency (bin by bin), then the conversion should work....no?

[johnsold]

No. Because of spectral leakage some components appear in multiple bins.  Calculating RMS on a bin by bin basis does not correctly account for the energy in each component. This is aggravated if the spectral leakage of separate components over lap in some bins.

Lynn