Specifications

3 Designing Controllers Using the Design Tool GUI
3-28
than the cumulative value. Increasing this weight forces the controller to make smaller,
more cautious adjustments.
Plant Inputs for Modified Rate Weight
Plant Inputs for Modified Rate Weight shows that increasing the rate weight from 0.1 to
0.3 decreases the move sizes significantly, especially the initial move (compare to Plant
Inputs for the T Setpoint Scenario).
Setting the rate weight to 0.1 yields a faster approach to the T setpoint with a small
overshoot, but the initial T
c
move is about six times larger than needed to achieve the
new steady state, which would be unacceptable in most applications (not shown; try it).
Note The controller minimizes the sum S
y
(k) + S
Δu
(k). Changes in the coolant
temperature have unequal effects on the two outputs, so the steady-state output
deviations won't be equal, even when both output weights are unity as in Plant Outputs
for T Setpoint Scenario with Added Data Markers.
Input Weights
The controller also minimizes the weighted sum of manipulated variable deviations from
their nominal values, computed according to