How to find phase difference (*jpg attached) ?

[sbomy]

I measured accelerations using 4 accelerometers at the same time (as attached *.txt file).

Based on the FFT analysis, all of them has 29 and 58 Hz as dominant frequencies

(*.jpg file shows the time domain signal, corresponding to the second column in *.txt file,  and its FFT from the second accelerometer.).

In order to use the measured signals as the input to a FE model, I want to find the phase differences among them.

I found one program source to find the phase difference, but that program is only for very smooth sine wave, not for my case.

Should I filter out the noise of high frequency to find phase difference more easily?

Hope to see a helper for my problem soon. Thank you.
 

[rpursley8]

Take the FFT of each of the signals and take a look at the phase (not just the magnitude) at the frequencies of interest (I assume 29 and 58 Hz).  This should give you the phase relationship between them.

[sbomy]

Randall,

Thank you for the reply. Would you please tell me how I see the phase difference in FFT analysis?

As far as I know I used FFT to find the magintude components. Thank you.

[Henrik_Volkers]

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sbomy wrote:

As far as I know I used FFT to find the magintude components.

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Time for a brain update 🙂

wiki Frequency Domain

 wiki DFT

[rpursley8]

The output of the FFT vi is complex and you have to convert it to magnitude and phase to view it.  The Amplitude and Phase. vi outputs it that way for you.