User`s guide

8 Model Analysis
What Does a Frequ
ency-Response Plot Show?
System Identic
ation Tool GUI supports the following types of
frequency-resp
onse plots for linear parametric m odels , linear state-space
models, and nonp
arametric frequency-response models:
Bode plot of the
model respo nse. A Bode plot consists of two plots. The top
plot shows the m
agnitude
G
by which the transfer function G magnies
the amplitude
of the sinusoidal input. The bottom plot shows the phase
ϕ=argG
by which the transfer function shifts the input. The input to
the system is a sinusoid, and the output is also a sinusoid with the same
frequency.
Bode plot of the disturbance model, called noise spectrum. Thisplotisthe
same as a Bode plot of the model response, but it shows the frequency
response of the noise model instead. For more information, see “Creating
Noise-Spectrum Plots” on page 8-40.
(Only in the MATLAB Command Window)
Nyquist plot. Plots the imaginary versus the real part of the transfer
function.
The following gure shows a sample Bo de plot of the model dynamics, cre ated
in the System Identication Tool GUI.
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