1. Introduction to Industrial Control Systems
Chapter 1

2. Objectives List the classifications of industrial control systems
Describe the differences among industrial control systems and provide examples of each type
Define common terms associated with industrial control systems

3. Objectives (cont’d.)
Describe the differences between open- and closed-loop systems
Define common terms associated with open- and closed-loop systems
List the factors that affect the dynamic response of a closed-loop system
Describe the operation of feed-forward control

4. Objectives (cont’d.)
List three factors that cause the controlled variable to differ from the setpoint

5. Industrial Control Classifications
Motion control
Automatic control system that controls the physical motion or position of an object
Process control
One or more variables are regulated during the manufacturing of a product
Two categories:
Batch processing
Continuous process

6. Open- and Closed-Loop Systems
Open loop system
Simple
Must be manually balanced
Examples
Closed loop system
Self-correcting and self-regulating
Used by most automated processes

7. Elements of Open- and Closed-Loop Systems
Common terms:
Controlled variable
Measured variable
Measurement device
Feedback signal
Setpoint
Error detector
Error signal
Controller
Actuator
Manipulated variable
Manufacturing process
Disturbance

8. FIGURE 1-5 Closed-loop block diagram that shows elements, input/output signals, and signal direction

9. FIGURE 1-6 Open-loop block diagram that shows elements, input/output signals, and signal direction

10. Feedback Control
Error must exist before some corrective action can be made
Causes of errors:
The setpoint is changed
A disturbance appears
The load demand varies
Signals may be positive or negative

11. Practical Feedback Application
Heat exchanger
FIGURE 1-8 Closed-loop temperature control system

12. Dynamic Response of a Closed-Loop System
Measure of loop’s corrective action
Factors:
Response time
Time duration
Static inertia of controlled variable
Leads to pure lag
Dead time

13. Feed-Forward Control Prevent errors from occurring
Minimize not prevent
Also use feedback control
Typically used only in critical applications within the plant

14. FIGURE 1-9 Feed-forward control of a temperature control system

15. FIGURE 1-10 Feed-forward control loop with a feedback control loop