01-15-2009 04:51 PM
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?
Sunny
01-20-2009 11:56 PM
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