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

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Fluxshot
Fluxshot 2019-11-18
回答： Star Strider 2019-11-18
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.

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回答（1 个）

Star Strider
Star Strider 2019-11-18
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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