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How to plot ifft for a frequency signal?

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Priyom Goswami
Priyom Goswami 2021년 8월 5일
댓글: Yazan 2021년 8월 6일
I've a .dat file (attaching the .mat file of that .dat file after converting, since this platform doesn't allow to upload .dat file while asking question) which represent the frequency spectrum of a vibration signal from a bearing having a sampling frequency of (fs=32768). How to convert the frequency signal to time domain signal. Please help.
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Scott MacKenzie
Scott MacKenzie 2021년 8월 6일
Have you tried? Please post the code you've attempted so far.

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Yazan 2021년 8월 6일
편집: Yazan 2021년 8월 6일
clc, close all
fs = 32768;
fidx = z.Date23122013;
specOneSide = z.Time100351;
[fidx, idx] = unique(fidx);
specOneSide = specOneSide(idx);
fOneSide = (fidx./fidx(end))*fs/2;
plot(fOneSide, specOneSide), xlabel('Frequency - Hz'), ylabel('Magnitude spectrum');
axis tight, title('One-sided spectrum');
specTwoSide = [flip(specOneSide(1:end)); specOneSide(2:end-1)];
N = length(specTwoSide);
f = -fs/2:fs/N:fs/2-fs/N;
plot(f, specTwoSide), xlabel('Frequency - Hz'), ylabel('Magnitude spectrum');
axis tight, title('Two-sided spectrum');
sig = ifft(fftshift(specTwoSide));
t = (0:N-1)./fs;
plot(t, sig), axis tight, title('Signal');
xlabel('Time - sec'), ylabel('Amplitude');
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Yazan 2021년 8월 6일
Notice that the values of the Date23122013 (or your frequency axis points) are not unique. Also, for one value of Date23122013, you have sometimes multiple values of Time100351. My code uses the first appearing value of Time100351 for a given Date23122013 automatically, which is sometimes zero, but you might prefer otherwise. It is always a good idea to clean your data first.

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