I use some industrial amplifier modules where each of them amplifies force transducers. All amplifiers are powered by a single power supply and the output. Amplifier is set to 6kHz filter. And there is no anti-aliasing filter in the system.
Interest of frequency is max 10Hz and the sampling rate is 500Hz. Sometimes when the noise noise appears at the sampled outputs it has a peak around 3.1Hz. So this corrupts the readings below 10Hz.
I took some offset readings to observe the electrical noise better.
I have the following 12 seconds of noisy signal in time series:
And here 1 second view:
And below is the FFT of the signal:
And finally comparison when that 3.1Hz noise, green when it is there and the blue plot when it is not there:
I still could not find the source of this noise.
But just by looking at these plots, what can that 3.1Hz noise be? Can that be aliasing? If so, is there a way to estimate the real noise freq. by looking at the peaks at FFT given that we only have 500Hz sampling rate?