Use the dialog box to specify model order, delay and feedthrough characteristics. If you
are unsure about the order, select Pick best value in the range, and enter a range of
orders. In this case, when you click Estimate in the Plant Estimation tab, the software
displays a bar chart of Hankel singular values. Choose a model order equal to the number
of Hankel singular values that make significant contributions to the system dynamics.
When you choose a state-space model structure, the identification plot shows a plant
response (blue) curve only if a valid estimated model exists. For example, if you change
structure after estimating a process model, the state-space equivalent of the estimated
model is displayed. If you change the model order, the plant response curve disappears
until a new estimation is performed.
When using the state-space model structure, you cannot directly interact with the model
parameters. The identified model should thus be considered unstructured with no
physical meaning attached to the state variables of the model.
However, you can graphically adjust the input delay and the overall gain of the model.
When you select a state-space model with a time delay, the delay is represented on the
plot by a vertical orange bar is shown on the plot. Drag this bar horizontally to change the
delay value. Drag the plant response (blue) curve up and down to adjust the model gain.
Choosing Identified Plant Structure