User`s guide

1 Data Processing
Getting Advice About Your Data
You can use the advice command to get information about your
time-domain or frequency-domain data. This command does not support
frequency-response data.
Note If you are using the System Identification Tool GUI, you must e xport
your data to the MAT LAB workspace before you can use the
advice command
on this data. For more information about exporting data, see “Exporting
Models from the GUI to the MATLAB Workspace” on page 12-13.
Suppose that data is an idda ta obje ct. advice(data) displays the following
information about the data in the MATLAB Command Window. Ask yourself
the following questions:
• Doesitmakesensetoremoveconstantoffsetsandlineartrendsfromthe
data? See also
detrend.
• Wh at are the excita tion levels of the signals and how does th is affects the
model orders? See also
pexcit.
• Isthereanindicationofoutputfeedbackinthedata? Seealso
feedback.
When feedback is present in the system, only predictio n-error methods
work well for estimating closed-loop data.
To estimate the delay from the i nput to the output in the system (dead time)
by using the data, use the
delayest command. You need to kno w the delay
when specifying a model s tructure for estimation.
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