Problem in FFT and harmonics analysiation

Question

s p 2017-3-27

0
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https://ww2.mathworks.cn/matlabcentral/answers/332181-problem-in-fft-and-harmonics-analysiation

回答： Star Strider 2017-3-27

Hi everybody. I am new to analysis field . I have ust started working on Vibration analysis .I got my datas recorded for mislignment of shaft and want to convert these datas to frequency domain.I tried using FFT to get frequency domain using this

% read data data = xlsread('Healthy20Hztime');

%Frequency Analysis

time = data(:,1); % sampling time

signal = data(:,2); % signal data in Time-Domain

L=length(signal); % Length of signal

Ts=time;

Fs=20000; % sampling frequency

NFFT = 2^nextpow2(L); % Next power of 2 from length of y

Y = fft(signal,NFFT)/L;

a =2*abs(Y(1:NFFT/2+1));

f = Fs/2*linspace(0,1,NFFT/2+1);

figure(1),

plot(f,2*abs(Y(1:NFFT/2+1))); % Plot single-sided amplitude spectrum.

grid off

title(' Healthy 20Hz');

xlabel('Frequency (Hz)');

ylabel('|Y(f)|');

xlim([0 1000]);

Now I would like to get 1x 2x 3x harmonics of these data . Can somebody help me in getting my codes right as well help me find out the harmonics 1x 2x 3x.

Thanks