I am acquiring vibration data from an accelerometer using a DAQ. Due to some reason I am seeing spurious peaks/impacts in the FFT spectra at specific frequency and its harmonics all the way till the Nyquist frequency. This frequency changes with the sampling rate as follows:
- Sampling rate = 48 KHz, peaks at 100 Hz and its harmonics
- Sampling rate = 8 KHz, peaks at 83.33 Hz and its harmonics
- Sampling rate = 24 KHz, peaks at 93.75 Hz and its harmonics
These peaks don't seem to correspond to any real mechanical/vibration source. Initially I suspected aliasing, but it seems the DAQ has anti-aliasing built-in. I also tried doing anti-aliasing in software using python/scipy.signal.decimate(), but it didn't help.
I am attaching below couple of FFT spectra plots for the 24 KHz case.
Can you please advise what could be possible reason for such spurious FFT peaks?