User`s guide

Identifying Low-Order Transfer Functions (Process M odels)
If you prefer to specify parameter constraints directly in the estimator syntax,
thefollowingtableprovidesexamplesof
pem commands.
Action
Exampl e
Fix the value of K to 12.
m=pem(ze,'p1d','k','fix','k',12)
Initialize K for the iterative search
without fixing this va lue.
m=pem(ze,'p1d','k',12)
Constrain the value of K between
3 and 4.
m=pem(ze,'p1d','k',...
{'min',3},'k',{'max',4})
Options for Specifying the Process-Model Structure
This section describes h ow to specify the model structure in the estimation
procedures “How to Estimate Process Models Using the GUI” on page 3-23
and “Estimating Process Models at the Command Line” on page 3-29.
In the System Identification Tool GUI. Specify the m odel structure by
selecting the numbe r of real or complex poles, and whether to include a z ero,
delay, and integrator. The resulting transfer function is displayed in the
Process Models dialo g b ox .
At the comm a nd line. Specify the model structure using an acronym that
includes the following letters and numbers:
• (Required)
P for a process model
• (Required)
0, 1, 2 or 3 for the number of poles
• (Optional)
D to include a time-delay term
e
sT
d
−
• (Optional) Z to include a process zero (numerator term)
• (Optional)
U to indicate possible c o m plex -v alued (underd am ped ) poles
• (Optional)
I to indicate enforced integration
3-35