I have a signal that varies in time as shown below. I have just shown a 5 s interval of data (from 97 s to 102 s). The sampling frequency is 1000 Hz.
My goal is to find out the frequency of the downward peaks in the signal. I used a peak-finding algorithm to detect the peaks in the signal and it turned out that there were about 33 peaks in the 5-second interval – i.e. approx 6.6 every second.
How do I get this information using the Fourier transform? When I plot the power spectral density, I get a peak at 0. Looks like I am doing something wrong. Should I apply some sort of a smoothing function to get rid of noise? Or is there a frequency associated with the system at all?