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wrobelek
Poland
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 Posted - 03/18/2004 : 10:37:48 AM
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how can I use a graph result of FFT? what does it mean Angle(deg)?
where is the score of frequency? |
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wrobelek
Poland
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Posted - 03/18/2004 : 12:04:00 PM
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| Can anybody help me, and explain, how can I use FFT to count frequency? |
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Mike Buess
USA
3037 Posts |
Posted - 03/18/2004 : 12:44:34 PM
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Angle(deg) refers to the phase angle. The plot shows the amplitude (layer 1) and phase (layer 2) of the fourier transformed results. If the plot name is FFTPlot1 then the data are contained in the worksheet FFT1 which has 6 columns:
Freq, Real, Imag, r, Phi, Power
Frequency values are in the first column. Select the Real and Imag columns and then Plot->Line to see the Real and Imaginary values versus frequency.
...Your original FFT plot may have only displayed the values for positive frequencies.
Mike Buess
Origin WebRing Member
Edited by - Mike Buess on 03/18/2004 12:47:27 PM |
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wrobelek
Poland
Posts |
Posted - 03/19/2004 : 09:05:42 AM
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| Thank you, but my problem did not disappeared. I have lot of different peaks on my graph.I want to know how can I count a main frequency of their. Where a result is? I want to know which of there are real peak or noise? |
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Mike Buess
USA
3037 Posts |
Posted - 03/19/2004 : 09:52:28 AM
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The Analysis->FFT command in Origin 7.0 and 7.5 appears to have a bug which prevents the amplitude plot from showing. In that case your Amplitude vs Frequency graph will be empty. Is that what you mean? If so you can do this to show the amplitude plot in a new graph...
1. Right-click anywhere inside the Angle(deg) graph at the top of the FFT graph window and select "Go to FFT1" (the FFT number may be different) on the context menu. That will bring up the worksheet that contains the FFT data. (I described that worksheet in my previous post.)
2. Select (highlight) column r(Y) in the FFT worksheet.
3. Select Line on the Plot menu. That will create a new plot of amplitude versus frequency.
Mike Buess
Origin WebRing Member |
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easwar
USA
1965 Posts |
Posted - 03/19/2004 : 2:55:44 PM
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quote:
The Analysis->FFT command in Origin 7.0 and 7.5 appears to have a bug which prevents the amplitude plot from showing.
Hi Mike,
I did a quick test and could not reproduce this problem. Can you provide more details?
wrobelek, you say you see a lot of different peaks cannot determine what is noise and what is real...FFT does not distinguish this automatically for you. All it will provide is the frequency spectrum. You need to decide. There are various filter utilities in Origin under the Analysis->FFT Filter menu, such as lowpass, high pass, threhsold filter etc. Maybe you could try those instead?
Easwar
OriginLab
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Mike Buess
USA
3037 Posts |
Posted - 03/19/2004 : 3:49:26 PM
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Hi Easwar,
This is how it works for me starting with a worksheet with 3 columns... A(X), Real(Y), Imag(Y).
1. Select the Real and Imag columns. (Or plot those columns.)
2. Analysis->FFT
3. Settings tab...
Sampling, Real and Imaginary datasets identified correctly
Sampling Interval correct
Rectangular Window
Normalize unchecked, Shift and Unwrap checked
Exp phase factor = -1
4. Operation tab...
Forward FFT
Amplitude Spectrum
5. On OK I get a plot of phase data in layer 2 and nothing in layer 1. Layer Contents dialog for layer 1 also lists nothing although the r dataset is available on the left.
...I doubt that it matters, but the worksheet had 512 rows.
...It appears that one of my own DialogBuilder dialogs interferes with the FFT dialog. The amplitude plot shows up fine when I close my dialog before doing the FFT.
Mike Buess
Origin WebRing Member
Edited by - Mike Buess on 03/19/2004 4:04:31 PM
Edited by - Mike Buess on 03/19/2004 4:35:29 PM |
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FFT