| T O P I C R E V I E W |
| cristinaRaspone |
Posted - 07/24/2011 : 05:39:44 AM
Origin Ver. and Service Release (Select Help-->About Origin):
Operating System:
Hello to everyone!
I've got some questions about the FFT:
I've got a column on 10000 values that represent the position of a generic point A of a beam vibrating. i've copied this column in the second column of Origin's workpage. then simply i clicked on analysis-->FFT and "magically" I get amplitude and phase graphics.
but my question is: is this way to proceed correct? Have I to insert another column in which I specify which is the time domain corresponding to the signal in the second column?
And, how can I understand which is the scale for units along axes?for example, along x axis, 0.2....Hertz? ...milliHz?
sorry if my questions are stupid..
Hope someone could spend his/her time to help me!
Thank you in advance!!!!! |
| 1 L A T E S T R E P L I E S (Newest First) |
| easwar |
Posted - 07/25/2011 : 4:48:58 PM
Hi,
You did not mention which version of Origin you are using, so I will assume it is the latest: 8.5.1
You can download the evaluation version of 8.5.1 if you wish to try that.
If you put no numbers in the 1st column and your data is in 2nd column (where typically col1 is X and col 2 is Y), then in the FFT dialog the sampling interval will be shown as 1, so Origin assumes the time steps is 1 second. Then in the results the frequency numbers represent Hz.
If you know your time data, you should fill column 1 with the desired numbers. For example you can open script window (menu: Window->Script window) and type:
col(1)={0:0.1:10}
and press Enter, for example to fill col 1 with numbers 0, 0,1, 0,2....up to 10. Then do the analysis again and in the dialog the sampling interval will show 0.1 which means 0.1 sec and the output is still to be interpreted as in Hz.
Now, in the latest version, you can ALSO put in Units information in your time column. So if you enter "sec" then the output graph will be marked as Hz, and if you enter "ms" the output graph will be marked as kHz etc. Some standard notations for sec, ms etc are recognized. If you enter anything else for the units that is not recognized, the output graph axis will be marked as (1/what-you-enetered).
So, if no units entered, the input X is assumed to be sec and output is assumed to represent Hz.
Hope this helps.
Easwar
OriginLab
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