Section 1 Basic Control Loops

Question 1

Control System

Answer 1

A group of components that work together in order to maintain a certain process variable or a set point.

Question 2

What are the objectives of a control system?

Answer 2

1) Maintain product quality
2) Maintain safe operating conditions
3) Maintain economic production by minimizing down time

Question 3

Disturbance

Answer 3

An undesired change that is introduced into the system without the operator that adversely affects the controlled variable

Question 4

Feedback Control

Answer 4

Error driven control system in which the control signal to the actuator is proportional to the difference between the command signal and the feedback signal

Question 5

What are the advantages of a manual control system?

Answer 5

1. Control system is less likely to become unstable as it is controlled by an operator
2. Allows for more control during start up or unusual conditions

Question 6

What are the disadvantages of manual feedback control?

Answer 6

Human error can occur due to distraction, improper indicator reading, or the speed of reaction

Question 7

What are the advantages of an automatic control loop?

Answer 7

1. The controller never gets distracted
2. The system is fast acting
3. The set point is interpreted more consistently

Question 8

What are the disadvantages of automatic control loops?

Answer 8

1. The controller reacts only after an upset happens to the system
2. Control loops can be unstable if the gain is not tuned properly

Question 9

Feedforward Control

Answer 9

Method of control that compensates for disturbances before they affect the process variable.

Question 10

What are the disadvantages of forward feedback control?

Answer 10

1. There is no knowledge whether the output is correct.
2. Disturbances needs to be compensated for perfectly to maintain an accurate set point.