FFT plot

[hussey]

hi

i am trying to plot a FFT of signal to find diffrent frequency of non periodic signal.

kindly help to plot Frequency Vs. Amplitude.

attached file have time Vs amplitude data

[johnsold]

The Freq. indicator does not indicate frequency.  Read the Detailed Help file for Buneman Frequency Estimator.vi  The beta output must be scaled by df = fs/N = 1/(dt*N) where df is the frequency increment, dt is the time interval between successive samples, and N is the number of samples or the size of the array. When I scale the result appropriately for your data, I get 3254.48 Hz which apears to be reasonable.

To get a spectral plot you can use any of the Spectral or FFT VIs. In any case you will need to scale the result by the timing just as is required for the Frequency Estimator.

Lynn

[hussey]

hi

can you teach me, that how you have program in block diagram panel.

it will be great help for me

[johnsold]

Other than cleaning up some of the code I changed two items.

dt is calculated from the difference of the first two elements of the time data array.

The spectrum is calculated from the amplitude array by Amplitude and Phase Spectrum.vi. A property node is used to scale the X-axis to frequency.

Lynn

[hussey]

hi

the graph you have shown in picture form provided data is not showing same result as  in your last uploaded VI

kindly check it again.

[johnsold · Accepted solution]

Is this what you are seeing?

The image I posted previously is the same graph and the same data, only the maximum of the X-axis scale was changed to 100000 from 100000000.  Just select the maximum value with the typing tool and enter the new value. This does not change the data in any way. It only changes the portion of the data which is visible in the display.

Lynn

[hussey · Accepted solution]

Yes 

exactly