Matlab Pwelch: Converting dB/Hz to PSD Acceleration Units

In summary, to convert the dB/Hz values to acceleration units, use the equation Acceleration = 10^(dB/20) * sqrt(2) * (1/sqrt(Fs)) and plot the values on the Y axis in acceleration units.
  • #1
19dan87
6
0
Hi,
I am simulating vibrations in simulink and processing my results in matlab. I am trying plot the PSD for my acceleration results using pwlech method.
When I plot the PSD plots from the methods below
(NOTE:I have a sampling rate of 0.006 so that means I am using a sample frequency of Fs=1/0.006=166)
Pwelch(x,[],[],2024,fs)
Or [Pxx,f]=pwelch(x,[],[],2024,fs) plot(f,Pxx)
The results on the Y axis are in the form of dB/Hz. How do I changed the plot/results so that I can plot PSD acceleration, ie. ms^-2 back . I want to show the plots in the form of the units used in the simulations.

Thanks
Dan
 
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  • #2
To convert the dB/Hz values to acceleration units, you will need to use the following equation: Acceleration = 10^(dB/20) * sqrt(2) * (1/sqrt(Fs)) where Fs is your sample frequency. You can then plot the values on the Y axis in acceleration units.
 

1. What is Matlab Pwelch and how does it work?

Matlab Pwelch is a function used for estimating the power spectral density (PSD) of a signal. It works by dividing the signal into segments, computing the periodogram for each segment, and then averaging the periodograms to obtain an estimate of the PSD.

2. Why is unit conversion necessary when using Matlab Pwelch?

Unit conversion is necessary because Matlab Pwelch outputs the PSD in units of power per frequency, which may not be the desired unit for the application. Converting the units allows for easier interpretation of the results.

3. How do I specify the units for the frequency axis in Matlab Pwelch?

The frequency axis units can be specified by using the 'FrequencyNormalization' parameter in the function call. The options for this parameter include 'psd' (default), 'rad/sample', or 'radians'. For example, to specify the frequency axis in units of Hz, use 'FrequencyNormalization','psd'.

4. Can I change the window length in Matlab Pwelch?

Yes, the window length can be changed by using the 'Window' parameter in the function call. The default window length is 8 segments, but this can be adjusted to fit the specific needs of the signal being analyzed.

5. How do I interpret the results from Matlab Pwelch?

The results from Matlab Pwelch represent the power spectral density, which is a measure of the power of a signal as a function of frequency. The higher the power at a specific frequency, the more energy is present at that frequency in the signal. This can be useful for identifying dominant frequencies in a signal or detecting changes in frequency over time.

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