Control Systems PPT 1

FEEDBACK AND CONTROL SYSTEM
By: Engr. Ivy Ramos

INTRODUCTION
CONTROL SYSTEM
is consist of subsystems and processes ( or plants) assembled

for the purpose of controlling the output of a process.
is an arrangement of physical components connected or related

is such a manner as to command, direct, or regulate itself or
another system.
System - is an arrangement, set or collection of things or

related in such a manner as to form an entire or whole.
Control - usually taken to mean regulate, direct or command.

DEFINITION
It means by which a variable quantity or set of variable

quantities is made to conform to a prescribed norm. It
either holds the values of the controlled quantities
constant or causes them to vary in a prescribed way.
A control system may be operated by electricity, by

mechanical means, by fluid pressure (liquid or gas), or by
a combination of means. When a computer is involved in
the control circuit, it is usually more convenient to
operate all of the control systems electrically, although
intermixtures are fairly common.
ADVANTAGE OF CONTROL SYSTEM
o Power Amplification
o Remote Control
o Convenience of Input form
o Compensation for disturbances
TYPES OF CONTROL SYSTEMS
Open loop control systems
Closed loop control system

OPEN LOOP CONTROL SYSTEM
In open loop control system we have a process which we

have to control and some input to change the process and
out put. We have an example of a tank level control
Hi level
Start/ switch
stop
Low
level
switch
OPEN LOOP CONTROL SYSTEM
Functional Block Diagram
Command Reference Reference Reference Output

Input Selector Input Selector
Physical Arrangement
Input Motor Powering Control Output or

Controller
Device Effort Load
OPEN LOOP CONTROL
Control action is independent
In open loop control system when we start the pump it

will continue fill the fluid in the tank but at a time tank
will overflow still pump will not stop. In open loop
control we have no feedback that what is going on in
process.
We have to manually control the pump by putting a man

at near the tank .He will see that if the high level switch
glow then he will stop the pump and if lo level will glow
then he will start the pump.
ADVANTAGES OF OPEN LOOP SYSTEM
The open loop systems are simple and economical.

They are easier to construct.
The open loop systems are stable.
OUTSTANDING FEATURES OF OPEN LOOP SYSTEM
Their ability to perform accurately is determined by

calibration.
They are not usually troubled with problem of instability.
DISADVANTAGES OF OPEN LOOP SYSTEM
The open loop systems are inaccurate and

unreliable.
The changes in the output due to external
disturbances are not corrected automatically.
CLOSED LOOP CONTROL
is one in which the control action is

dependent on the output.
have information about the change in

process with respect to change in input.
Now consider the previous example in
open loop control system.
more commonly called the feedback control

system.
CLOSE LOOP CONTROL SYSTEM BLOCK DIAGRAM
Functional Block Diagram
Actuating Signal
Command Reference Reference Dynamic Output

Input Selector Input Element
Feedback
Element
Physical Arrangement
Command Error Power

Controller
Input Detector Device
Output
Output or Load
Measuring Device
Input - is the stimulus, excitation or command
applied to a control system, typically from an
external source, usually in order to produce a
specified response from the control system
Output - is the actual response obtained from the

control system. It may or may not be equal to the
specific response implied by the input.
Feedback - is that property of a closed loop

system which permits the output (or some other
control variable) to be compared with the input to
the system so that the appropriate control action
may be performed as some function of the output
and input.
Characteristic of Feedback
1. Increase accuracy (the ability to faithfully
reproduce the output)
2. Tendency towards oscillation or instability
3. Reduce the sensitivity of the ratio of output to
input to variations in system parameters and
other characteristics.
4. Reduce the effects effects of nonlinearities.
5. Reduce effects of external disturbances or
noise.
6. Increased bandwidth.
ADVANTAGES OF CLOSED LOOP
SYSTEM
Closed loop systems are accurate.
They are accurate even in the presence of nonlinearity.
They are more stable.
They are less affected by noise.
DISADVANTAGES OF CLOSED LOOP SYSTEM
They are complex and expensive.

The feedback in closed loop system may leave to
oscillatory response.
More care is needed to design a closed loop system.
The overall gain of the system is reduced due to feedback.
CLOSED LOOP CONTROL
In open loop control system when we start the pump we
have no status of the tank level but in closed loop control
we have status of tank level and if tank level goes below,
low level switch act and the pump will start by controller.
In second case if the tank level goes high then the high
level switch act and controller stop the pump. Hence the
difference between the open loop and closed loop control
system
EXAMPLES OF CONTROL SYSTEMS
Distinct examples of control systems are as follows:
Liquid level control system
Room temperature control system
Traffic control system
Home heating systems
CONTROL SYSTEM ENGINEERING PROBLEM
Analysis - is the investigation of the properties

of an existing system
Design Problem - it the choice and arrangement

of system components to perform a specific task.
METHODS FOR DESIGN:

by analysis - modifying the characteristics of an
existing or standard system configuration.
by synthesis - defining the form of the system
directly from its specification
CONTROL PROBLEMS CAN BE DIVIDED INTO
1. A set of performance specifications must be
established
2. As a result of the performance specifications a
control problem exist
3. A set of differential equations that describe the
physical system must be formulated.
4. The performance of the basic (or original) system is
determined by application of one of the methods of
analysis (or combination of them)
5. If the performance of the original system does not
meet the required specifications, equipment must be
added to improve the response.
6. The achievement of optimal performance for the
required system response specification may be required.
This system is referred to as system optimization.
STATEMENT OF CONTROL SYSTEM
1. The physical system processed is to be
controlled through closed loop or feedback
operation.
2. The output variable called response is adjusted
as required by the error signal.
3. Error signal is the difference between system
response measured by sensors and the reference
signal, which is response.
4. Controller is needed to filter the error signal.
SOLVING CONTROL PROBLEMS INVOLVES
1. Choosing sensor to measure the output.
2. Choosing actuators
3. Developing sensor equations or models
4. Designing the controller based on the developed
models and control criteria.
Control Criteria:
a. Disturbance rejection
b. Steady state errors
c. Transient response
d. Sensitivity to parameter changes
5. Evaluating the design analytically by stimulation
and finally testing the physical system
6. If the physical tests are satisfactory then repeat the
steps
ANALOG AND DIGITAL CONTROL SYSTEM
A signal dependent on continuum

of values of the independent
variable t is an continuous-time,
continuous-data, or analog signal
A signal defined at, or interest at,
only discrete (distinct) instants of
the independent variable t is a
discrete-time, discrete-data,
sampled-data, or digital signal
Combination is called hybrid
ANALOG AND DIGITAL CONTROL SYSTEM
Continuous-time control systems,

continuous-data control system, or
analog control systems, contains or
process only continuous-time(analog)
signals and components.
Discrete-time control system, discrete-
data control system, or sampled-data
control system, have discrete-time
signal or components at one or more
points in the system
CONTROL SYSTEM MODELS OR
REPRESENTATION
Mathematical models
Block diagrams
Signal flow graphs

EXAMPLES:
THANK YOU!!

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FEEDBACK AND CONTROL SYSTEM

By: Engr. Ivy Ramos

is consist of subsystems and processes ( or plants) assembled

is an arrangement of physical components connected or related

System - is an arrangement, set or collection of things or

Control - usually taken to mean regulate, direct or command.

It means by which a variable quantity or set of variable

A control system may be operated by electricity, by

Open loop control systems

Closed loop control system

In open loop control system we have a process which we

Functional Block Diagram

Command Reference Reference Reference Output

Input Motor Powering Control Output or

Control action is independent

In open loop control system when we start the pump it

We have to manually control the pump by putting a man

The open loop systems are simple and economical.

OUTSTANDING FEATURES OF OPEN LOOP SYSTEM

Their ability to perform accurately is determined by

The open loop systems are inaccurate and

is one in which the control action is

have information about the change in

more commonly called the feedback control

Command Reference Reference Dynamic Output

Command Error Power

Output - is the actual response obtained from the

Feedback - is that property of a closed loop

They are complex and expensive.

Analysis - is the investigation of the properties

Design Problem - it the choice and arrangement

METHODS FOR DESIGN:

A signal dependent on continuum

Continuous-time control systems,

Signal flow graphs

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