Phase shift between two signals with cross-correlation
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Good afternoon everyone. I have two time signals representing vibration measurements from two sensors and I would like to know the phase shift between them. These two signals come from a rotating device. My idea is to use cross-corelation between them so that I can find the time lag but I have a few questions:
1. Do I have to filter out the noise in the signals?
2. The signals contain a dominant harmonic and multiple of it + other harmonics. Can I still use xcorr? As I have seen many applications on the web and on this forum but all ofthem are for deterministic/pure waves signals.
If you need any additional information to answer just let me know.
Thank you
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Star Strider
on 17 Jan 2018
You will have to experiment with your signals to see if filtering them is necessary. If you get acceptable results without filtering, you can obviously avoid that step.
Filtering has its own problems if you are interested in the phase relationships. If you are using an IIR filter, use the filtfilt function to do the filtering, since it is phase-neutral for all filters. (It is not necessary for zero-phase FIR filters, and you can use filter with them.)
Two Signal Processing Toolbox functions that you may find helpful are finddelay (link) and alignsignals (link). (I believe these were introduced in R2015. The documentation does not say specifically.)
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Star Strider
on 18 Jan 2018
I am not certain. For a full explanation of what finddelay does and how it works, I refer you to the documentation section on Algorithms (link).
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