The document discusses open loop and closed loop control systems. It defines an open loop system as one where the controller's input is independent of the system's output, as there is no feedback loop. The advantages are simplicity and lower cost, but errors and disturbances cannot be corrected. A closed loop system uses feedback, so the controller can adjust the input based on the output to improve accuracy. It is more complex and costly than open loop, but can correct for errors and disturbances to keep the output closer to the desired value.

1. Name:- Amrit Singha
Roll NO:- 27501621058
Semester:- 5Th
Subject Name-:- Control System
Subject Code:- PC EE 503
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2. Open Loop System Definition:
An open-loop system is a type of control system in which
the output of the system depends on the input but the input
or the controller is independent of the output of the system.
These systems do not contain any feedback loop and thus
are also known as non-feedback system.
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3. Open Loop Description
In the open-loop control system, a reference input is given to the system in order to get the desired output. But the
achieved output is not considered by the system for further reference input.
In this figure here represents the block diagram
of an open-loop control system.
Here as we can see that the system consists of
two blocks, one is the controller while other is
controlled process.
Basically, according to the required output, an
input is provided to the controller of the system.
Depending on the achieved input, the controller
generates the control signal which is fed to the
processing unit. Thus according to the control
signal, proper processing is performed and
output is achieved.
But as there is no feedback path present in the system, thus whether the achieved output is desired or not
the input has nothing to do with it.
So, this is the reason we say that in an open-loop system the input is independent of the output.
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4. Example with Transfer Function
We all are aware of the operation of a traffic light controller present at various road crossings.
Basically the three signals generated by the controller is time-dependent. An internal timing is provided to the
controller at the time of designing the system. So, when the traffic signal controller is installed at the crossing
then each signal is displayed by the controller timely, independent of the rush present on any of the side.
Basically relays are used to provide timing sequence to the system.
In this figure clearly indicates that whatever output is achieved, the input will remain independent of it.
We know transfer function is given as:
When we separately consider the transfer function of each block then it will be given as:
Thus the overall transfer function will be:
So, the open-loop gain will be:
The use of the open-loop control system indicates that the operator of the system is ready to consider
some minimal deviation in the output from the expected value.
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5. Open Loop Advantages And Disadvantages
Advantages
 These systems possess simplicity
in construction and ease of
maintenance.
 Due to the lesser number of units,
overall the system is economic.
 The output provided by the
system shows stability.
 The operation is quite convenient.
Disadvantages
 These systems require timely
recalibration.
 The systems are more prone to
errors.
 The changes in the desired output
can be the result of internal or
external disturbances.
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6. Closed-Loop Control System Definition:
A closed-loop control system is a type of control
system in which the controlling action shows
dependency on the generated output of the
system. In simple words, in these systems, the
output of the system controls the input applied to
the system.
The variation in input according to the output leads
to produce more accurate system output. Thus
controllability in the closed-loop system is achieved
through the output generated by utilizing a
feedback path.
Now the controlling provided to the system can be either output independent or output dependent. This
variation leads to give two different categories of control system.
A system in which controlling action is independent of the generated system output is known as open-loop
control system. While in a closed-loop system, the produced output controls the functioning of the system by
the used of feedback
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7. Transfer Function of Closed-Loop Control System
Transfer function indicates the behaviour of the system as it is
defined as the mathematical relation between the input and
output of the system.
The gain of the system defines the ratio of output to input. Thus
we can say the output of the system is the product of transfer
function and input.
So, for the above-given system figure:,
On substituting the value of E(s) in the 1st equation
On transposing
This is the transfer function of a closed-loop system
with negative feedback.
For a positive feedback system, it is given as:
For a unity feedback system (i.,e H(s) = 0) with a high value of gain. The transfer function is unity.
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8. Advantages:
 Closed loop control systems are
more accurate even in the
presence of non-linearities
 The sensitivity of the system may
be made small to make the
system more stable
 The closed loop systems are less
affected by noise.
Disadvantages:
 Closed loop control systems are
costlier and complex
 The feedback in the closed loop
system may lead to oscillatory
response
 The feedback reduces the overall
gain of the system
 Stability is the major problem in
the closed loop system and more
care is needed to design a stable
closed loop system.
Close Loop Advantages And Disadvantages
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9. Comparison of Close Loop And Open Loop Control
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