Introduction to
Industrial Control
Systems
Chapter 1
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
Objectives (cont’d.)
• Describe the differences between openand 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
Objectives (cont’d.)
• List three factors that cause the controlled
variable to differ from the setpoint
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
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
Elements of Open- and ClosedLoop Systems
• Common terms:
– Controlled variable
– Measured variable
– Measurement device
– Feedback signal
– Setpoint
– Error detector
– Error signal
– Controller
– Actuator
– Manipulated variable
– Manufacturing
process
– Disturbance
FIGURE 1-5 Closed-loop block diagram that shows elements, input/output signals, and
signal direction
FIGURE 1-6 Open-loop block diagram that shows
elements, input/output signals, and signal direction
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
Practical Feedback Application
• Heat exchanger
FIGURE 1-8 Closed-loop temperature control system
Dynamic Response of a ClosedLoop System
• Dynamic response:
– Measure of loop’s corrective action
• Factors:
– Response time
– Time duration
– Static inertia of controlled variable
• Leads to pure lag
– Dead time
Feed-Forward Control
•
•
•
•
Prevent errors from occurring
Minimize not prevent
Also use feedback control
Typically used only in critical applications
within the plant
FIGURE 1-9 Feed-forward control of a temperature control system
FIGURE 1-10 Feed-forward control loop with a feedback control loop
True or False Questions.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Automatic control system that controls the physical motion or position of
an object is known as Motion control. T F
In Process control, only one variable is regulated during the
manufacturing of a product. T F
Open loop system are complicated. T F
A Closed loop system must be manually balanced. T F
In Feedback control, Error must exist before some corrective action can
be made. T F
Feedback control signals are positive only. T F
A practical application of a Feedback control would be an Heat
Exchanger. T F
One factor that would affect the Dynamic response of a closed loop
system would be response time. T F
Feed-Forward Control does NOT prevent errors from occurring. T F
Dynamic response is the measure of loop’s corrective action. T F