Chapter 20    Multiloop Control: Effects of Interaction

Home    Index

Check Your Reading             Study Questions             Thought Questions

The questions will be categorized according to the key concepts in the chapter.

Modelling Controllability
Interaction Dynamics & Stability

 

 

 

 

 

 

 

 

 

 

Check Your Reading

Solidify the Concepts
20.1
All multivariable control is implemented with many single-loop PID controllers, (i.e., multiloop control).

Controllability

TRUE            FALSE

 

 

 

 

 

 

 

 

20.2
We often select multiloop control design because it

Controllability

Every plant should operate safely with only multiloop control.

 

 

gives the best performance

 

 is the only possible approach.
 

 retains the well know PID controller.
 
 is simple to implement by the engineer and to use by the operator.

 

 

 

 

 

 

 

 

 

 

20.3
Process interaction occurs when

Interaction

Note: Interaction is important in multivariable control!

 

one CV influences more than one CV

 

 one valve influences more than one CV
 

 one valve influences all CV's
 
 always exists, there is no need to check.

 

 

 

 

 

 

 

 

 

 

20.4
Processes with multiple manipulated and controlled variable can be modelled

Modelling
Recall that we use modelling to understand the process and design controls.

 

using only empirical methods

 

 

 using only fundamental methods
 

 using either fundamental or empirical methods
 
by copying a model from the textbook

 

 

 

 

 

 

 

 

 

 

20.5
The operating window is

Modelling

 



 

a window for observing the plant from the control building.

 

 

 a two-dimensional plot of process variables
 

 a range of attainable steady-state values for process variables.

 

 

 

 

 

 

 

 

 

 

 

20.6
A process is controllable, as defined by Marlin (2000), if

Controllability

 



It is possible to maintain CV(t) = SP(t) throughout a dynamic transient.

 



It is possible to maintain CV =SP at a new steady state after a disturbance
 

 It is possible to maintain CV =SP at a new steady state after a disturbance using PID control

 

 

 

 

 

 

 

 

 

 

20.7
The relative gain provides an indication of

Interaction

 

 

How process gains change due to interaction

 



 

All types of interaction
 



 

Two way interaction
 
Deviation of multiloop from single-loop dynamic behavior

 

 

 

 

 

 

 

 

 

 

20.8
Interaction affects stability for multi-loop control.

Dynamics

TRUE            FALSE