2. Contents
• Introduction
• Important terms
• Types of Systems
1) Open loop system
2) Close Loop system
• Comparison of Systems
• Requirements of a good control system
• Feed Forward system
• Design Process
3. Introduction
• Control system are an integral part of our lives and play very important
role.
• From a simple bread toaster to complex power plant, control system are
all around us and inseparable part of modern society.
• Launching a satellite in orbit, regulating a power plant, tracking enemy
on radar are some of man made control system..
• Control system occur in nature also. Human body is a great example of
complex Control system, because we've so many control system by
nature i.e. respiratory, Digestive system etc.
4. Important terms
• Control system : A control system is an arrangement or a combination
of various physical components, also called sub-systems, connected in
such a manner so as to attain a certain objective.
• Input : The excitation applied to the system from an external source to
attain a output is called input signal
• Output : The actual signal attain from system is called output signal.
• Control action : is a quantity responsible for activating the system.
Control
system
Input Output
Fig.(1) Basic Block Diagram of Control System
5. Must have things in the control system:
1. Inputs
2. Outputs
3. An arrangement of subsystems to achieve the input-output
combination
There are two types of systems depending on the configuration of
components:
1) Open loop system 2) Close loop system
6. Open loop system
• Those systems in which the output has no effect on the control
action are called open-loop control systems. i.e. It doesn’t
automatically correct the changes in the output
• A system in which control action is independent of the output of the
system is called as open loop system.
• In open loop system, the output remains constant for a given input
provided the external conditions are the same.
• There is no connecting action taking place in an open loop system
i.e. No Feedback
Controller PlantInput
Signal
Output
7. • Examples of Open loop system
Electric Hand Drier
Automatic Washing Machine
Bread Toaster
• Advantages
1) Simple Construction & Design
2) Economic
3) Easy maintenance
4) Stability
• Disadvantages
1) Incorrect and unreliable
2) Internal Disturbance
3) Recalibration is required time to time
8. Close loop system
• A system in which the control action is dependent on the output is
called close loop system. In close loop system the output is constantly
monitored and adjusted to the required value by the system.
• The output signal is fed back and compared to the reference input.
• Depending upon the difference between the output signal and reference
input, corrective actions can be taken by the controller to adjust the
output.
• i.e. Air-conditioning unit
Transducer Controller
Sensing device/
Feedback element
PlantInput Output
9. • Example of close loop system
Automatic Electric Irons
Voltage Stabilizer
DC motor speed control by Tachometer
Missile Launcher
• Advantages
1) Accuracy is high
2) Reduced effect of non-linearties
3) High Bandwidth
4) Facilitates Automation
• Disadvantages
1) Complicated in design and maintenance costlier
2) Problem of Stability
10. Comparison of Open loop and Close loop system
Sr.
No.
Open Loop System Close loop System
1. No feedback. Hence feedback
element is absent.
Feedback exists. Hence feedback
elements are exists.
2. No error detector. Error detector is present.
3. It is inaccurate. It is accurate.
4. Highly sensitive to parameter
changes.
Less sensitive to parameter
changes.
5 Small bandwidth. Large bandwidth.
6. Stable. May become unstable.
7. Economical. Costly.
8. Examples: Coffee maker, hair drier Example: Guided missile, servo
voltage stabilizer
11. Feed forward System
• In feed forward systems the output of one stage of control system is
sent to improve the overall performance of control system. It is used
whenever there is disturbance.
Feed
Forward
System
System
Sensor
Disturbance
Input
signal
Outpu
t
signal
12. The Design Process
Physical
system
Draw a
functional
block
diagram
Convert
into a
schematic
Obtain a
precise
block
diagram
or signal
flow chart
Get a
transfer
Function
Analyze by
checking for
stability and
see if
specification
s are met
