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Difference between Calculating Power Spectrum and Power Spectrum Density of a Signal

Updated Jul 25, 2019

Reported In

Software

  • LabVIEW

Issue Details

I have a time signal that I want to do spectrum analysis, and I'm trying to test the power spectrum and PSD VI. What is the difference between the power spectrum and the power spectral density in the export mode of this VI?

Solution

The FFT Power Spectrum and PSD VI located on Signal Processing>>Waveform Measurement sub-palette on the Function palette have export mode input terminals that allow you to select the power spectrum and power spectral density.

Measuring the power spectrum of a time signal illustrates which frequencies contain the signal's power. The measure is the distribution of power values as a function of frequency where "power" is considered to be the average of the signal's energy. In the frequency domain, this is the square of the FFT's magnitude.

 

A Power Spectral Density (PSD) is the measure of signal's power content versus frequency. A PSD is typically used to characterize broadband random signals. It can be looked upon as a frequency-domain plot of power per unit Hz vs. frequency.
Therefore, while the power spectrum calculates the area under the signal plot using the discrete Fourier Transform, the power spectrum density assigns units of power to each unit of frequency and thus, enhances periodicities. 

 

In the previous version of LabVIEW, the power spectrum measurement of the time signal was performed using the FFT Power Spectrum VI and the FFT Power Spectral Density VI which are in Signal processing >> Waveform measurement in the function palette as shown in the figure below. and have been replaced by PSD VI.