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02-25-2010 07:54 AM

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Dear all,

I am doing a project on finding other transform (except FFT) to find out harmonics in the waveform. I hope someone can tell me the methods. I have found a lot of time on internet and got no result. Thanks.

Victor

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02-26-2010 12:43 PM

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Hi Victor-

The FFT is conceptually a fairly straight-forward algorithm. It basically measures the distance between every peak in your signal and tallies the results in a graph. You see spikes at the resonant and harmonic frequencies. I don't know that there are any other transforms to find the harmonics of a system.

Maybe I am not fully understanding the question, but I don't know of any other transforms that will get what you need.

Best of luck with your application!

Gary P.

Applications Engineer

National Instruments

Visit**ni.com/gettingstarted** for step-by-step help in setting up your system.

Applications Engineer

National Instruments

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02-26-2010 12:59 PM

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Hello Victor,

If perhaps you are working with rotating machines where the frequency of an "n times per revolution" event is dependent upon the speed of the machine, you may want to look at Order Analysis.

Events that occur a given number of times per revolution occur at the same position each revolution regardless of the rotational speed. However, the frequency at which they occur is directly related to the rotational speed. Order Analysis removes this speed dependency by transforming the phenomena from the time-based domain into a position-based domain.

In the position-based domain, the recurring events are displayed as a the "number of times the event occurs per revolution" instead of the "number of times the event occurs per second" (i.e. frequency). At least this is my interpretation of it based on my experience.

Best Regards,

Chris