The document discusses control systems, differentiating between open loop and closed loop systems. Open loop systems operate without feedback, making them simple and economical but inaccurate, while closed loop systems use feedback for improved accuracy and reliability despite being more complex and costly. Additionally, it outlines the requirements for a good control system, including accuracy, sensitivity, noise reduction, stability, bandwidth, and speed.

2. Contents
 Open Loop Control Systems
 Closed Loop Control Systems

3. What is “controlling”?
 To cause a machine or process to
function in a predetermined manner.
 To energize or de-energize an output
 To set a data table bits to on or off a
machine, by a user program.

4. What is a Control System?
 A control system is a system of devices or set
of devices, that manages, commands, directs
or regulates the behaviour of other device or
system to achieve desire results.
 A control system is a system, which controls
other system.
ProcessInput Output

5. Control System
Open Loop
Control
System
Close Loop
Control
System

6. Open Loop Control System
Controller Process

7. A control system in which the
output has no effect on the control
action.
Do not provide feedback of the
actual state of the system.
There is no comparing of output
with the input for control purposes.
The action is totally independent of
output of the system.

8. Applications of Open Loop Control System
 Electric Hand Drier
 Automatic Washing Machine
 Bread Toaster
 Automatic Tea/Coffee Maker
 Timer Based Clothes Drier
 Light Switch
 Volume on Stereo System

9. Advantages
 Simple in construction and design.
 Economical.
 Easy to maintain.
 Generally stable.
 Convenient to use as output is difficult to
measure.

10. Disadvantages
 Open loop control systems are
inaccurate.
 These are not reliable.
 Any change in output cannot be
corrected automatically.
 These are slow

11. Closed Loop Control System
Controller Process Output
Command
Signal,
Setpoint
Measurement
+
-
Error

12.  Control system in which the output
has an effect on the input quantity.
A closed loop system is called a
feedback control system.
It provides feedback of the actual state
and compare it to the desired state of
the system.
The input quantity will be adjusted
based on the output generated to
produce the desired output response.

13. Applications of Closed Loop Control
System
Automatic Electric Iron
Servo Voltage Stabilizer
Water Level Controller
Missile Launched & Auto Tracked by
Radar
An Air Conditioner
Cooling System in Car

14. Advantages
 This system is more reliable
 A number of variables can be handled simultaneously.
 Closed loop control systems are more accurate even in the
presence of non-linearity.
 Highly accurate as any error arising is corrected due to
presence of feedback signal.
 Bandwidth range is large.
 Facilitates automation.
 The sensitivity of system may be made small to make
system more stable.
 This system is less affected by noise.

15. Disadvantages
 They are costlier.
 They are complicated to design.
 Required more maintenance.
 Feedback leads to oscillatory response.
 Overall gain is reduced due to presence of feedback.
 Stability is the major problem and more care is needed to design a stable
closed loop system.

16. Requirement Of Good Control System
 Accuracy:
error detector should be present in control system to increase
accuracy
 Sensitivity :
It should be sensitive to input signal only
 Noise :
control system should be able tor reduce noise effect for better
performance
 Stability:
system must be able to remove offset
 Bandwidth:
bandwidth should be large as possible for frequency response
 Speed :
This is the time taken by control system to achieve its stable

17. Open Loop vs. Closed Loop
Open loop control system Closed loop control system
1
The feedback element is
absent
The feedback element is always
present
2
An error detector is not
present
An error detector is always
present
3 It is stable one. It may become unstable
4 Easy to construct Complicated construction
5
It is an economical
It is costly
6 Small bandwidth Large bandwidth
7
It is inaccurate
It is accurate
8
Less maintenance
More maintenance