How can I get the FFT (Amplitude - Frequency) from Time (s) - Acceleartion(m/s^2) data?

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Bob
Bob on 21 Mar 2016
Commented: Star Strider on 21 Mar 2016
clc;
clear all;
close all;
Time = xlsread('Data','A2:A513'); % Time (s)
Acceleration = xlsread('Data','B2:B513'); % Acceleration (m/s^2)
n = length(Acceleration);
Ts = Time(2)-Time(1); % Sample Time
Fs = 1/Ts; % Sampling Frequency
NFFT = 2^nextpow2(n); % Next power of 2 from length of data
Y = fft(Acceleration,NFFT)/n;
f = Fs/2*linspace(0,1,NFFT/2+1);
plot(f,Y)
xlabel('Frequency (Hz)')
ylabel('Amplitude (m)')
I am trying to get the FFT from Time Acceleration Data.
Error using plot
Vectors must be the same length.
P.S I have attached the Data.xlsx

Accepted Answer

Star Strider
Star Strider on 21 Mar 2016
In your code, ‘f’ is half the length of ‘y’ so you need to create an ‘index vector’.
Try this:
... CODE ...
Y = fft(Acceleration,NFFT)/n;
f = Fs/2*linspace(0,1,NFFT/2+1);
Iv = 1:length(f); % Index Vector
plot(f,abs(Y(Iv)))
xlabel('Frequency (Hz)')
ylabel('Amplitude (m)')
That should work.
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