Estimating damping ratio from frequency domain

[FReich]

Hello,

I aquire a signal and run a FFT.

To gain the damping ratio out of the FFT curve, I want to use the half-power bandwidth method.

Does anyone know about that? How can I do that with LabView?

Thanks

Franziskus 

[jcrooke]

For the lightly damped system damp ratio is approx. 1/2Q, where Q = f(res) / (f(high) - f(low)).

f(high) and f(low) are the half power points. They are the points where the squared magnitude of the response (your FFT values) are one half of the peak value, i.e. the value at the resonance frequency f(res).

If the FFT array is called g, then you want amgSqrd_g = (abs(g))^2 and then find the max and the two points nearest max that are nearest to or below the half max value.

Try the attached vi. I haven't tested it, but it may provide a starting place for you.

[laplace_transform]

Hello

What is FArray in this program?

Thanks

Moin

Q&dampFactCalculator.vi (45 kb)