Acceleration vs Time data into FFT

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nur yusof
nur yusof 2015-1-17
评论： nur yusof 2015-1-21
I have acceleration vs time data. I want to get FFT value from the data.Can someone show me the way?

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Image Analyst
Image Analyst 2015-1-17
spectrum = fft(signal);
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nur yusof
nur yusof 2015-1-18
I import the data into matlab. Thats means the coding should be spectrum = fft(signal); plot(1:N,abs (spectrum));
Is it true??
nur yusof
nur yusof 2015-1-21
I got the FFT value from your coding image analyst.Is the bandwidth of FFT data according to my time history domain data?If not,how to ensure the bandwidth is within the interval?Can you brief me about the coding? My bandwidth range is 50Hz-500Hz from time domain history data.

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Shoaibur Rahman
Shoaibur Rahman 2015-1-17
Define the number of DFT points N, and then perform the fft.
N = pow2(nextpow2(length(signal)));
y = fft(signal,N);
plot(1:N,abs(y))
If the length of your signal is a big number then set the value of N manually to a lower value, like N = 64, 128, 256, etc. This will make your figure to look better sometime, but note that that may not be accurate always from the computational point of view.
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nur yusof
nur yusof 2015-1-18
Attached previous figure is solve by Shoaibur's coding. While, attached figure solve by image analyst.I dont know why the figure look like that.I think the frequency solve by Shoaibur is high maybe due to the the vibration of bridge,vehicle and noise from environment.So, it has high value.
nur yusof
nur yusof 2015-1-21
I got the FFT value from the coding.Is the bandwidth of FFT data according to my time history domain data?If not,how to ensure the bandwidth is within the interval?Can you brief me about the coding? My bandwidth range is 50Hz-500Hz from time domain history data.

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