MATLAB: How to convert time domain data to frequency domain by using FFT.

fft

Hello all,

I am having the turbine shaft data in time domain.(Time And velocity in Amplitude)

i have plotted the values and got the waveform for the same data and it is matching with the analyzer data. Next is to do the FFT of it.will anyone help me to formulate this to fft.

figure,plot(time,Velocity)
figure,plot (abs(fft(velocity)))

——–so what should i do next———– i am not getting fft of it

Best Answer

fft(amplitude) already gives you the frequency domain information.

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The y-axis on a PSD estimate will not be in units of the time squared, it will be in amplitude squared per Hz, so for an ECG signal I assume that will be in millivolts, not milliseconds. The recorded values of the waveform are not in time.

Since you are using dspdata.psd, why not just use spectrum.periodogram?

    psdest = psd(spectrum.periodogram,ecg,'NFFT',length(ecg),'Fs',fs);
    plot(psdest)

If you want to plot without using dB (that is preferred by the way)

   plot(psdest.Frequencies,psdest.Data)

MATLAB: FFT of vibration data

     Fs = 800; % sampling rate of 1000 Hz
     t = 0:1/Fs:1-1/Fs;
     x = ad2;
     xdft = fft(x);
     xdft = xdft(1:length(x)/2+1);
     DF = Fs/length(x); % frequency increment
     freqvec = 0:DF:Fs/2;
     plot(freqvec,abs(xdft))

I hope this can work

Best Answer

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