# Torque signal fft

I have the following torque signal picked up with a 10.240Hz sampling rate from a testbench.

I am studying its fft which I create on Octave with the following code:

ftpar=fft(torque);

nfft=length(ftpar);

freqtpar=abs(ftpar)/nfft;

freqt2par=freqtpar(1:nfft/2);

mediapar=freqt2par(1);

freqt2par=2*freqt2par(2:end);

deltafreq=Fs/nfft;

xfft=[deltafreq:deltafreq:(Fs/2-Fs/nfft)];

plot (xfft.',freqt2par);


When looking at the 10 frequencies with the biggest amplitudes the one at the lowest frequency is at 24 Hz all of the others are at higher frequencies. However, by looking at the time domain graph there seems to be a big oscillation with around a 0.5 Hz frequency.

Where is that oscillation coming from? Am I missing something when doing the fft? The lowest frequency I get from the fft is 0.08 Hz so I should be seeing that kind of frecuency.