Chapters 1-4

Question 1

What is a process/system?

Answer 1

Series of physical elements that interact to perform functions.

Question 2

What is a dynamical system?

Answer 2

System exhibiting continuous motion in the face of internal or external forces

Question 3

What are state variables?

Answer 3

The smallest possible subset of system variables that can represent the internal conditions of the process.

Question 4

What are input variables?

Answer 4

The variables that independently induce change in the internal conditions of the process.

Question 5

What are controlled variables?

Answer 5

The variables that are controlled; also called output variables

Question 6

What are manipulated variables?

Answer 6

These input variables that are at our disposal to manipulate freely.

Question 7

What are disturbance variables?

Answer 7

Input variables over which we have no control.

Question 8

What is control

Answer 8

Act of adjusting the manipulated variable to keep the controlled variable at a desired value (while satisfying some constraints).

Question 9

What is the set point?

Answer 9

The desired value referring to controlled variables

Question 10

Which variable is measured in feedback control?

Answer 10

The Control variable

Question 11

Which variable is not measured in feedback control?

Answer 11

Disturbance variable

Question 12

What is a limitation of feedback control?

Answer 12

No action is taken until after the disturbance occurs

Question 13

Are disturbance variables known in feedback control?

Answer 13

No

Question 14

Which variable is measured in feedforward control?

Answer 14

Disturbance variable

Question 15

Which variable is not measured in feedforward control?

Answer 15

Control variable

Question 16

What is an important advantage of feedback control?

Answer 16

They reduce sensitivity of the controlled variable to
unmeasured disturbances and process changes.

Question 17

What is an advantage of feedforward control?

Answer 17

Action is taken before
the controlled variable deviates from the set point.

Question 18

What are three significant disadvantages of feedforward control?

Answer 18

(i) - the disturbance variable must be measured/modelled (or
accurately estimated)
(ii)- no corrective action is taken
for unmeasured/unmodelled disturbances

(iii) a process model
is required.

Question 19

What is the difference between feedback and feedforward control in terms of corrective action?

Answer 19

FB: Corrective action is taken after process is affected (something goes wrong)

FF: Corrective action is taken before the process is affected

Question 20

What does feedforward control not take corrective action of?

Answer 20

Unmeasured disturbance

Question 21

For feedback control, does corrective action depend on the source of disturbance?

Answer 21

No. Corrective action occurs regardless of the source of disturbance.

Question 22

How is the disturbance dealt with in a system with feedforward (FF) + feedback (FB) control?

Answer 22

FF deals with the most significant disturbance.

FB deals with the rest of disturbance.

Question 23

For definining variables of the first letter for control methods, define what each letter stands for: T, L, F, P, and A

Answer 23

T -> temperature
L -> level
F -> flow
P -> pressure
A -> analyzer/concentration

Question 24

For definining variables of the second letter for control methods, define what each letter stands for: T, C

Answer 24

T - transmitter
C - controller

Question 25

Explain how feedback control works?

Answer 25

-CV is measured
-DV is not measured

-No action is taken until after the disturbance occurs.

Question 26

Explain how feedforward control works?

Answer 26

-CV is not measured
-DV is measured

-Requires measuring and modelling DVs.

-No action is taken against DV’s that aren’t modelled.

Question 27

When is feedforward control ideal to use?

Answer 27

It’s ideal in a theoretical sense that controller can take action via MV even while CV remains equal to its desired value.

Question 28

Can laplace transform model a time delay?

Answer 28

Yes. This is known as the time delay property of the Laplace transform

Question 29

Is time delay a linear operation or a non-linear one?

Answer 29

Time delay is a linear operation, not a non-linear one.

Question 30

Explain why the following statement is false?: “The model for a system should be made as accurate as possible since a better model means better control.
“

Answer 30

The more accurate your model the more complex your design is and consequently the more expensive it is. Often a simpler model will do fine and cost less to implement