You can generate an FFT (fast-Fourier-transform) plot by periodically collecting a large number of conversion samples from the output of an ADC. Typically, ADC ...
A Fast Fourier Transform (FFT) plot is generated by collecting a large number of conversion samples from the output of the A/D converter in a periodic fashion that is receiving an AC input signal.
Closed-loop control systems are sometimes shipped from the factory with resonances and other operational difficulties that aren't supposed to be part of the package and are not well understood.