Units for Magnitude after Fast Fourier Transform (FFT) is done

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Hi all,
I am currently doing vibration analysis for Air Compressors.
I have collected the vibration data signals using accelerometers which gives acceleration units in m/s^2.
My query is that I do not know what is the unit of the Magnitude in the frequency domain plot through the followings codes;
Code.JPG
X1 is my Magnitude axis (Y-axis) and f1 is my frequency axis (X-axis).
Any form of help to answer my question on the magnitude is appreciated. Thank you.

Answers (1)

Star Strider
Star Strider on 18 Nov 2019
The magnitude units are the same as the time-domain amplitude units, unless you transform them in some way (such as squaring to diisplay power). However the fft function splits the spectrum into negaitive-frequency and positive-frequency regions (most easily seen using fftshift as you have done), and this divides the energy of the signal so that half the amplitude appears in the negative -frequency region and half in the positive-frequency region. So the true amplitude is 2 times the displayed amplitude.

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