Specifications

3 Designing Controllers Using the Design Tool GUI
3-40
For comparison, reset the two scenarios so that the only disturbance is a one-degree step
increase added to the measured reactor temperature. The modified controller (case 2) is
designed for such disturbances, and CSTR Outputs, Output Disturbance Scenarios 1 and
2 shows that it performs better, but the difference is less dramatic than in the previous
scenario. The default controller is likely to be best if the real process has multiple
dominant disturbance sources.
CSTR Outputs, Output Disturbance Scenarios 1 and 2
Define Soft Output Constraints
The discussion in “Weight Tuning” on page 3-24, defined temperature control as
the primary goal for the CSTR application. The predicted (but unmeasured) reactant
concentration, C
A
, could vary freely.
Suppose this were acceptable provided that C
A
stayed below a specified maximum (above
which unwanted reactions would occur). You can use an output constraint to enforce this
specification.
Start with a single controller identical to the InputSteps controller described in
“Disturbance Modeling and Estimation” on page 3-34. Rename it Unconstrained.
Right-click Unconstrained in the tree and select Copy. Rename the copy Yhard. Make
another copy, naming it Ysoft.