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I want to analyze vibrations and I am new to signal processing and I have many doubts, I use an accelerometer and FFT for this.

First, I don't know what frequencies to check and as a result, I don't know with what frequency sampling should be done. ---> I am sampling with a frequency of 400 Hz. I don't know if it is correct or not?

And secondly, I don't know what the minimum frequency is so that I can determine the sampling time accordingly and determine the block size.
--> As far as possible, I considered the maximum block size to be 8192. Will there be a problem? As far as I know, it can also improve the frequency resolution

Third, averaging was used to improve accuracy and repeatability But because I don't know whether the frequency content changes over time or not, is this averaging correct?

Jdip
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Ho3ein H K
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  • @DanBoschen The problem is that the frequencies can be different for different conditions, and if we want to sample once with the highest frequency for each case and then choose the appropriate frequency, the implementation process will be difficult and time-consuming. – Ho3ein H K Feb 07 '23 at 22:59
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    Unless you have some reason you want/need to sample lower, then sample all at the highest rate you can. Follow the guidance in the referenced link versus anti alias filtering. The only reason to sample lower is if you are memory limited and need a longer time duration. – Dan Boschen Feb 07 '23 at 23:56
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    (Basically when you know nothing about the waveform then you capture to the limits of your measurement device (sampling rate and duration), then with knowledge of the range of your measurement device you evaluate your result and from the evaluation you can usually determine if you need a higher quality measurement device (that can sample higher and longer) or if you can (if you wanted to) go the other way and reduce sampling rate and memory. Use the measurement to then make it into a signal you do know, from the measurement you can answer all your questions for your specific waveform.) – Dan Boschen Feb 08 '23 at 00:21
  • @DanBoschen I got it, when we don't know the signal, then we try to consider the best possible situation It means sampling with the highest possible frequency and the largest possible block size. and about part 3 of the Question is it better to do averaging? – Ho3ein H K Feb 08 '23 at 08:30
  • Same thing for the same reason - evaluate with and without the averaging to see if the signal is sufficiently stationary – Dan Boschen Feb 08 '23 at 10:25
  • I think this question is only partly a duplicate, and the part that isn't duplicate should be asked separately. – OverLordGoldDragon Feb 08 '23 at 12:44

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