Is it possible to get 3db bandwidth from bode plot?

[Jaeen]

I made vi for getting displacement values from raw acceleration data  and made bode plot from FFT . But the result output is string data . Is it possible to get 3db cutoff frequencies from string data? . Any other suggestions? 

[Bob_Schor]

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@Jaeen wrote:

I made vi for getting displacement values from raw acceleration data  and made bode plot from FFT . But the result output is string data . Is it possible to get 3db cutoff frequencies from string data? . Any other suggestions? 

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Please attach the VI you made for "getting displacement values from raw acceleration data".  How did you "make bode plot from FFT"?  Please attach a "picture" of the bode plot.  I'm also confused by "the result output is string data".  What do you mean by "result output"?  

If you plot an FFT with Gain in dB, you can find the frequency on the left and right of the peak where the gain drops by 3 dB and read off the frequency bandwidth.  (Note -- I'm not an engineer, so there may be a secret handshake I don't know about, but you could also Ask Google about 3 db Bandwidth and find out if it is more complicated than I made it out to be).

Bob Schor

[JÞB]

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@Jaeen wrote:

I made vi for getting displacement values from raw acceleration data  and made bode plot from FFT . But the result output is string data . Is it possible to get 3db cutoff frequencies from string data? . Any other suggestions? 

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You are not really making any sense.

You cannot perform a Fast Fourier Transform on anything other than Discrete Time series data as [X,Y] or Waveform Data as <t0, dt, [Y]> and its output will be spectral data as [Frequency, Magnitude] and [Frequency, Phase Response] (both of the elements of a Bode Plot.)  These things are all numeric or, possibly NaN.  They can not be strings or contain strings.

Even MY Magic 8-Ball says "Ask again." 

[Jaeen]

This is vi where output is Bode Plot . This vi gets input from acceleration and impact hammer. I wand to compute damping ratio values from half power method. I am making vi such that i could get cutoff frequencies from -3db method continuously. Is it possible to automate this process in labview because i need to do it in matlab for single instance of time, i want it continiously.

[altenbach]

We don't have any data.

Can you run your Vi until the bode plot contains data, then stop the VI, right-click the bode plot...data operations...make current value default. Copy that plot to a new VI and attach it here.

(Please don't maximize the front panel to the screen and clean up your diagram. Overlapping wires with many kinks going in all directions makes editing slow and error prone)