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What Is the Difference between Calculating Power Spectrum and Power Spectrum Density of a Signal?



Hardware: PXI/CompactPCI>>Controllers

Problem:
I have a time signal for which I want to do some spectral analysis such as calculate the FFT power spectrum and the power spectral density. What is the difference between these two measurements and how do I implement each in LabVIEW?

Solution:
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. In the frequency domain, this is the square of the FFT's magnitude. In LabVIEW the power spectrum of a time signal is computed using the function FFT Power Spectrum.vi found in the Functions Palette under Signal Processing»Waveform Measurements.

The power spectrum density is a positive real function of a frequency variable associated with a stationary stochastic process or a deterministic function of time that has units of power per Hz. 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 LabVIEW, the power spectrum density is calculated by using the FFT Power Spectrum Density.vi function found in the Functions Palette under Signal Processing»Waveform Measurements.

The example program attached below shows the calculation of both the power spectrum and the power spectrum density of a two-tone frequency wave.

Related Links:
Example: Power Spectrum Measurement

Attachments:

Power SpectrumvsPower Spectrum Density.vi






Report Date: 10/14/2008
Last Updated: 09/29/2017
Document ID: 4QDEEHC1

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