Two time signals FFT

[luckym]

Hello,

Could anybody please explain how to correct use FFT with two signals analysis? or give me some example?

What I want is to calculate these characteristics of two signals: coherence, cross spectrum, and phase. I will do measurement on a construction with several accelerometers to measure vibrations. I think it should be done with this type of analysis. I don't understand why the coherence is always 1. I've read  the document FFT use in diadem but this type  of analyse is not clear for me.

Thanks for help

Best regards 

Michal.

[Queue-tip]

For any pair of input and output channels, the coherence is 1 if you only have one time interval, as defined in the 'Time Interval' tab in the analysis function's dialog box. The 'Number of intervals' parameter specifies the number of intervals for the data channel to be analyzed. If you bump this value up, you should start seeing a more interesting coherence plot.

You can also play around with the 'Start' and 'Overlap (%)' parameters, as necessary for the signal processing algorithm you are seeking to implement.

Quentin S.

Applications Engineer

National Instruments