Course: Diploma in Electrical and Electronic Engineering

1. EEEC4340318 INSTRUMENTATION AND CONTROL SYSTEMS
Introduction To Control Systems
FACULTY OF ENGINEERING AND COMPUTER TECHNOLOGY
DIPLOMA IN ELECTRICALAND ELECTRONIC ENGINEERING
Ravandran Muttiah BEng (Hons) MSc MIET

2. 1
Introduction To Control Systems
Control engineering is based on the fundamentals of feedback theory
and linear system analysis, and it generates the concepts of network
theory and communication theory. Accordingly, control engineering
is not limited to any engineering discipline but is applicable to
aeronautical, chemical, mechanical, environmental, civil, and
electrical engineering.
A control system is an interconnection of components forming a
system configuration that will provide a desired system response.
The basis for analysis of a system is the foundation provided by
linear system, which assumes a course effect relationship for the
components of a system. A component or process to be controlled
can be represented by a block as shown in figure 1.

3. 2
Control
System
Input Output
Figure 1: Control system

4. 3
Based on some parameters, we can classify the control systems into the
following ways.
Continuous Time and Discrete-Time Control Systems
(1) Control Systems can be classified as continuous time control systems
and discrete time control systems based on the type of the signal used.
(2) In continuous time control systems, all the signals are continuous in
time. But, in discrete time control systems, there exists one or more
discrete time signals.
Single Input Single Output (SISO) and Multiple Input Multiple Output
(MIMO) Control Systems
(1) Control Systems can be classified as SISO control systems and MIMO
control systems based on the number of inputs and outputs present.
(2) SISO control systems have one input and one output. Whereas, MIMO
control systems have more than one input and more than one output.
Classification Of Control Systems

5. 4
Open Loop and Closed Loop Control Systems
Control Systems can be classified as open loop control systems and closed
loop control systems based on the feedback path.
In open loop control systems, output is not fed-back to the input. So, the
control action is independent of the desired output.
Actuating
Device
Input Output
Actuating
Signal
Figure 2: Open loop control system
In open loop control systems, an input is applied to a controller and it
produces an actuating signal or controlling signal. This signal is given as an
input to a plant or process which is to be controlled. So, the plant produces
an output, which is controlled.
Process

6. 5
In closed loop control systems, output is fed-back to the input. So, the
control action is dependent on the desired output.
Controller
Input Output
Plant
Actuating
Signal
Figure 3: Negative feedback closed loop control system
The error detector produces an error signal, which is the difference between
the input and the feedback signal. This feedback signal is obtained from the
block feedback elements by considering the output of the overall system as
an input to this block. Instead of the direct input, the error signal is applied
as an input to a controller.
Error
Signal
Feedback
Signal
Feedback
Elements

7. 6
The controller produces an actuating signal which controls the plant. In this
combination, the output of the control system is adjusted automatically till
we get the desired response. Hence, the closed loop control systems are also
called the automatic control systems. Traffic light control system having
sensor at the input is an example of a closed loop control system.
Open Loop Control Systems Closed Loop Control Systems
Control action is independent of
the desired output
Control action is dependent of the
desired output
Feedback path is not present Feedback path is present
These are also called as non-
feedback control systems
These are also called feedback
control systems
Easy to design Difficult to design
These are economical These are costlier
Inaccurate Accurate
Table 1: The difference between the open loop and the closed loop control systems

8. 7
Figure 4 shows a temperature control of an electric furnace. The
temperature in the electric furnace is measured by a thermometer, which is
an analogue device. The analogue temperature is converted to a digital
temperature by an Analogue to Digital (A/D) converter. The digital
temperature is fed to a controller through an interface. This digital
temperature is compared with the programmed input temperature, and if
there is any error, the controller sends out a signal to the heater, through an
interface, amplifier and relay, to bring the furnace temperature to a desired
value.
Temperature Control Systems

9. 8
Analogue to
Digital
Converter
Interface
Relay Amplifier Interface
Input
Thermometer
Figure 4: Temperature control system

10. 9
Control System Design
Establish control goals
Identify the variables to control
Write the specifications for the
variables
Establish the system configuration
and identify the actuators
Obtain a model of the process, the
actuator, and the sensor
Describe a controller and select key
parameters to be adjusted
Optimise the parameters and analyse
the performance
Figure 5: Control system design process

11. 10
Figure 5 shows the control system design process.
(1) Variables to control are the quantities or conditions that are
measured and controlled.
(2) Process is a natural, progressively continuing operation marked by a
series of gradual changes that succeed one another in a relatively
fixed way and lead toward certain result or end.
(3) A system is a combination of components that act together and
perform a certain objective.
Control Systems Design Process

12. 11
DC Amplifier
Battery
Actuator
(DC Motor)
Control
Device
(Amplifier)
Process
(Turntable)
Turntable
DC Motor
Actual
Speed
Desired
Speed
Figure 6: Open loop control of speed of a turntable and a block diagram model

13. 12
DC Amplifier
Battery
Turntable
DC Motor
Figure 7: Closed loop control of the speed of a turntable
Tachometer

14. 13
Control
Device
Figure 8: Closed loop control system for disc drive
Actuator and
Read Arm
Sensor
Actual
Head
Position
Desired
Head
Position
Error
Design Example: Disk Drive Read System

15. 14
A hard disk uses round, flat disks called platters, coated on both sides
with a special media material designed to store information in the form
of magnetic patterns. The platters are mounted by cutting a hole in the
center and stacking them onto a spindle. The platters rotate at high
speed, driven by a special spindle motor connected to the spindle.
Special electromagnetic read/write devices called heads are mounted
onto sliders and used to either record information onto the disk or read
information from it. The sliders are mounted onto arms, all of which
are mechanically connected into a single assembly and positioned over
the surface of the disk by a device called an actuator. A logic board
controls the activity of the other components and communicates with
the rest of the computer.

16. 15
Figure 9: A hard disk

17. 16
Figure 10: Components of a hard disk

18. 17
Feedback Control Of An Antiaircraft Gun
Control
System
Gun
Dynamics
Figure 11: Feedback control of an antiaircraft system
Demanded Azimuth (Elevation)
Gun Azimuth (Elevation)

19. 18
Exercise 1
A precise optical signal source can control the output power level to
within 1 %. A laser is controlled by an input current to yield the output
power. A microprocessor controls the input current to the laser. The
microprocessor compares the desired power level with a measured
signal proportional to the laser power output obtained from a sensor.
Draw the block diagram representing the closed loop control system.
Micro-
processor
Laser
(Process)
Desired
Power
Output
Output
Power
Error Current
Figure 12: Microprocessor controls input current to laser
+
-
Sensor
(Measurement)
Measured
Power

20. 19
Exercise 2
Automated highways may be prevalent in the next decade. Consider
two automated highway lanes merging into a single lane, and describe
a control system that ensures that the vehicle merge with a prescribed
gap between two vehicles
Computer
(Controller)
Active
Vehicle
Desired
Gap
Actual
Gap
Error Brakes
Figure 13: A closed loop control system of an automated highway
+
-
Steering
Sensor
(Radar)
Measured Gap

21. 20
Problem 1
Many luxury automobiles have thermostatically controlled air-
conditioning system for the comfort of the passengers. Sketch a block
diagram of an air-conditioning system where the driver sets the desired
interior temperature on a dashboard panel.
Thermostat
(Controller)
Automobile
Cabin
Desired
Temperature
Cabin
Temperature
Error
Figure 14: Thermostatically controlled air-conditioning system
+
-
Sensor
(Measurement)
Measured Gap

22. 21
Problem 2
The role of air traffic control systems is increasing as airplane traffic
increases at busy airports. Engineers are developing air traffic control
systems and collision avoidance systems using the Global Positioning
System (GPS) navigation satellites. GPS allows each aircraft to know
its position in the airspace landing corridor very precisely. Sketch a
block diagram depicting how an air traffic controller might utilise GPS
for aircraft collision avoidance.
Autopilot
(Controller)
Allerons,
Elevators,
Rubber, and
Engine Power
Desired
Flight Path
From
Traffic
Controller
Flight
Path
Figure 15: Air traffic control systems and collision avoidance using GPS
+
-
Global
Positioning
System
Measured Flight Path
Aircraft
(Process)

23. 22
Problem 3
The potential of employing two or more helicopters for transporting
payloads that are two heavy for a single helicopter is a well-addressed
issue in the civil and military rotorcraft design arenas. A case of a
multi-lift arrangement wherein two helicopters jointly transport
payloads has been named twin lift as shown in figure 16. Develop the
block diagram describing the pilots action, the position of each
helicopter, and the position of the load.
Figure 16: Two helicopters jointly transport payloads
Load
1 2

24. 23
Radar
(Measurement)
Pilot Helicopter
Altimeter
(Measurement)
Desired
Separation
Distance
Desired
Altitute
Separation
Distance
Altitute
Measured Altitute
Measured Separation Distance
+
+
-
-
Figure 17: Control system for two helicopters jointly transport payloads

25. 24
Design Problem
Many cars are fitted with cruise control that, at the press of a button,
automatically maintains a set speed. In this way, driver can cruise at a
speed limit or economic speed without continually checking the speed
meter. Design a feedback control in block diagram for a cruise control
system.
Electric
Motor
1/k Valve Auto/Engine k
Shaft Speed
Meter
Controller
Desired
Speed
of Auto
Set by
Driver Desired
Shaft
Speed
Measured Shaft Speed
Drive
Shaft
Speed
+
-
Figure 18: Feedback control of automatic cruise control system

26. 25
References
(1) Richard C. Dorf and Robert H. Bishop, Modern Control Systems,
Prentice Hall, 2001.