Nyquist Analysis

NI System Identification

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Nyquist Analysis

Computes a Nyquist plot for a system model. This step computes the frequency response function (FRF) for one input-output pair of a system model. The step then presents the FRF with the real part versus the imaginary part, or Nyquist plot.

ParameterDescription
Nyquist plotDisplays the Nyquist plot of the system model.
Input ModelContains the following option:
  • Model—Specifies the estimated model to use for Nyquist analysis.
ConfigurationContains the following options:
  • Input source—Specifies the input source type to compute the transfer function. You can select stimulus or noise.
  • Graph Settings—Contains the following option:
    • Confidence level—Specifies the confidence interval of the FRF. The confidence radius equals confidence level times the standard deviations of the FRF. The default is 99%.
    • Magnitude unit—Specifies the type of scaling used for the magnitude axis. You can choose from the following scaling types:
      • dB (default)
      • linear
  • Frequency Information—Contains the following options:
    • Start frequency—Specifies the starting frequency of the Nyquist plot. The default is 0.01.
    • End frequency—Specifies the end frequency of the Nyquist plot. The default is 0.5.
    • Number of bins—Specifies the number of frequency points at which frequency responses are computed. The default is 1000.
    • Interval type—Specifies the type of scaling used for the frequency axis, or x-axis. You can choose from the following scaling types:
      • logarithmic (default)
      • linear
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