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What is the difference between power spectrum and PSD?

Hi all,

I input a time domain signal to the FFT power spectrum VI and FFT PSD VI seperately, and got two  outputs in frequency domain with similar shapes but different magnitudes.

I refer to some signal and system textbook, and find PSD(w)=1/pi*Power Specrum or equivalently PSD(f)=2* Power Specrum.But as I observed from the LabVIEW outputs, this relation is not correct. I input a 1KHz sin wave with amplitude=1, Fs=512KHz, #s=2048 , the PS peak is 0.5 and the PSD peak is around 0.013.

So I wondered what's the real formula LabVIEW is using to calculate PSD?



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PSD is related to spectrum resolution, thus related to sample rate.

df= Sample rate/ #samples

I think they follow this relationship:

Amplitude FFT power spectrum = Amplitude PSD * df * 1.5

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