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Create Chirp Input Signals

Create Chirp Signals Using Linear Analysis Tool

This example shows how to create a chirp input signal based upon a linearized model using the Linear Analysis Tool.

  1. Obtain a linearized model, linsys1.

    For example, see Linearize Simulink Model at Model Operating Point, which shows how to linearize a model.

  2. In the Linear Analysis Tool, in the Estimation tab, in the Input Signal drop-down list, select Chirp.

    The Create chirp input dialog box opens.

  3. In the System list, select linsys1. Click Compute parameters.

    The software automatically selects frequency points based on the dynamics of linsys1. The software also automatically determines other parameters of the chirp signal, including:

    • frequency range at which the linear system has interesting dynamics (see the From and To boxes of Frequency Range).

    • amplitude.

    • sample time. To avoid aliasing, the Nyquist frequency of the signal is five times the upper end of the frequency range, 2π5*max(FreqRange).

    • number of samples.

    • initial phase.

    • sweep method

    • sweep shape.

  4. Click OK to create the chirp input signal. A new input signal in_chirp1 appears in the Linear Analysis Workspace.

Create Chirp Signals Using MATLAB Code

Create a chirp signal in the most efficient way using a linear model that accurately represents your system dynamics:

input = frest.Chirp(sys)

sys can be the linear model you obtained using exact linearization techniques. You can also define a linear system based on your insight about the system using the tf, zpk, and ss commands.

For example, create a chirp signal from a linearized model:

magball
io(1) = linio('magball/Desired Height',1);
io(2) = linio('magball/Magnetic Ball Plant',...
               1,'output');
sys = linearize('magball',io);
input = frest.Chirp(sys)

The input signal is:

      FreqRange              : [0.0578598408615998 10065.3895573969] (rad/s)
      Amplitude              : 1e-005
      Ts                     : 0.00012484733494616 (sec)
      NumSamples             : 1739616
      InitialPhase           : 270 (deg)
      FreqUnits (rad/s or Hz): rad/s
      SweepMethod(linear/    : linear
                  quadratic/
                  logarithmic)

You can plot your input signal using plot(input).

For more information about chirp signal properties, see the frest.Chirp reference page.

The mapping between the parameters of the Create chirp input dialog box in the Linear Analysis Tool and the options of frest.Chirp is as follows:

Create chirp input dialog boxfrest.Chirp option
Frequency range > From First element associated with the 'FreqRange' option
Frequency range > ToSecond element associated with the 'FreqRange' option
Amplitude'Amplitude'
Sample time (sec)'Ts'
Number of samples'NumSamples'
Initial phase (deg)'InitialPhase'
Sweep method'SweepMethod'
Sweep shape'Shape'

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