1

PROGRAMMABLE LOGIC CONTROL (PLC) BASED

AUTOMATIC POWER SOURCE CHANGE OVER

A PROJECT REPORT

Submitted by

R.S.GOKULNATH (912312105008)

M.KALAIVANI (912312105011)

A.M.MEENAKSHI (912312105017)

In partial fulfillment for the award of the degree

Of

BACHELOR OF ENGINEERING

IN

ELECTRICAL AND ELECTRONICS ENGINEERING

SACS MAVMM ENGINEERING COLLEGE,

KIDARIPATTI, MADURAI-625301.

ANNA UNIVERSITY :: CHENNAI 600 025

APRIL 2016

2

ANNA UNIVERSITY :: CHENNAI 600 025

BONAFIDE CERTIFICATE

Certified that this project report “PROGRAMMABLE LOGIC CONTROL

(PLC) BASED AUTOMATIC POWER SOURCE CHANGE OVER” is the

bonafide work of “R.S.GOKULNATH (912312105008), M.KALAIVANI

(912312105011), A.M.MEENAKSHI (912312105017)” who carried out the

project work under my supervision

SIGNATURE SIGNATURE

Prof. G.EMILY MANORANJITHAM, Mr.N.KEERTHIVARMAN,M.E

M.E(Ph.D).,M.I.S.T.E.,

HEAD OF THE DEPARTMENT SUPERVISOR

Electrical & Electronics Engineering Electrical & Electronics Engineering

SACS MAVMM ENGINEERING SACS MAVMM ENGINEERING

COLLEGE COLLEGE

Kidaripatti, Madurai-625301. Kidaripatti, Madurai-625301.

Submitted for the “Viva –Voce” Examination Held On: ………………………

INTERNAL EXAMINER EXTERNAL EXAMINER

3

ACKNOWLEDGEMENT

“THE FEAR OF THE LORD IS THE BEGINNING OF WISDOM”

It is the grace of GOD that has helped us to complete this project in a

successful manner. It is foremost for us to be grateful to him. May his mercy

endure forever

We would like to express our sincere thanks to our beloved Principle,

Dr.S.NAVANEETHA KRISHNAN for his immense help in completing our

project.

We would like to express profusely our deep sense of gratitude to our Head

of the Department Prof. G.EMILY MANORANJITHAM.,M.E.,M.I.S.T.E.,

(Ph.D)., and our guide Mr.N.KEERTHIVARMAN, M.E who have extended

their heartedly encouragement, advice and valuable guidance throughout the

project.

We also express our deep sense of gratitude to our staff

Prof.P.MUTHU,M.E for his valuable guidance in all activities and playing a

major role for successful completion of this project.

We also thanks all other Faculty Members and Supporting Staffs of

Electrical and Electronic Department for their support and encouragement. Above

all we express our heartedly respect to our parents.

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ABSTRACT

The main objective of this project is to explain the uninterrupted power

supply to a load, by selecting the supply from different sources such as mains,

solar, inverter and generator automatically in the absence of any of the source. The

demand for electricity is increasing every day and frequent power cuts is causing

many problems in various areas like industries, hospitals and houses.

An alternative arrangement for power source is a must. This arrangement

can be designed by using PLC (Programming Logic Controller) and relays. When a

source, say mains fails the supply automatically shifts to next priority source solar.

When a source, say solar fails the supply automatically shifts to next priority

source generator and so on.

Use of PLC based automatic power source change over reduces the

operations time and reduces man power. Use of PLC results in faster operation and

accurate error detection thereby saving operating cost.

5

TABLE OF CONTENTS

CHAPTER NO TITLE PAGE NO

ABSTRACT IV

LIST OF FIGURES VII

LIST OF TABLES X

1 INTRODUCTION 1

1.1 PLC COMPARED WITH MICRO CONTOLLER 2

2 BLOCK DIAGRAM AND DESCRIPTION 6

2.1 BLOCK DIAGRAM 6

2.2 BLOCK DIAGRAM DESCRIPTION 6

3 HARDWARE DESCRIPTION 12

3.1 CIRCUIT DIAGRAM 12

3.2 CIRCUIT DIAGRAM DESCRIPTION 12

3.3. POTENTIAL TRANSFORMER CIRCUIT 14

3.4. OPERATIONAL AMPLIFIER 15

3.5. ULN DRIVER 20

6

3.6. TRANSISTOR AS A SWITCH 21

3.7 RELAY 22

3.8 VOLTAGE MEASUREMENT 24

3.9 VOLTAGE COMPARATOR 25

4 SOFTWARE DESCRIPTION 26

4.1. FUNDAMENTALS OF LOGIC 26

4.2. BASICS OF PLC PROGRAMMING 27

4.3. PLC PROGRAMMING LANGUAGE 29

4.4. TRUTH TABLE 35

4.5. LADDER DIAGRAM FOR SWITCH OVER 37

4.6. PLC LOGIC 38

5 PROGRAMMABLE LOGIC CONTROLLER (PLC) 39

5.1. HISTORY 39

5.2. DEVELOPMENT 40

5.3. TYPES OF PLC 41

5.4. STEPS FOR PLC OPERATION 42

5.5. PROGRAMMING 43

5.6. FUNCTIONALITY 44

5.7. PROGRAMMABLE LOGIC RELAY 45

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5.8. SCAN TIME 46

5.9. SYSTEM SCALE 46

5.10. USER INTERFACE 47

5.11. COMMUNICATIONS 47

5.12. DISCRETE AND ANALOG SIGNALS 48

5.13. PLC HARDWARE COMPONENTS 49

6 APPLICATION AND FEATURES OF PLC 54

6.1. APPLICATION OF PLC 54

6.2. FEATURES OF PLC 55

7 ADVANTAGES AND FUTURE SCOPE OF PLC 57

8 RESULT 58

9 CONCLUSION 59

REFERENCE 60

8

LIST OF FIGURES

FIG NO TITLE PAGE NO

2.1 BLOCK DIAGRAM 6

3.1 CIRCUIT DIAGRAM 12

3.2.1 DUAL POWER CIRCIT 13

3.2.3 7812 +VE REGULATOR IC 14

3.2.4 7912 –VE REGULATOR IC 14

3.3 POTENTIAL TRANSFORMER 15

3.4.1 SYMBOLIC DIAGRAM OF OP AMP 16

3.4.2 INVERTING MODE 17

3.4.3 NON-INVERTING MODE 17

3.4.4 IC –741 PIN DIAGRAM 18

3.5.2 ULN 2003 PIN DIAGRAM 21

3.7.1 ELECTROMAGNETIC RELAY 23

3.7.1.1 ELECTROMAGNETIC RELAY CONTACT 23

3.7.2 RELAY DIVER 24

3.8 VOLTAGE MEASUREMENT 25

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3.9 VOLTAGE COMPARATOR 25

4.1.1 LADDER DIAGRAM 26

4.2.1 LIFE CYCLE 28

4.3.1.1 SYMBOL DESCRIPTION 31

4.3.2 INSTRUCTION ADDRESS 32

4.3.3 BATCH INSTRUCTION 33

4.3.4 INTERNAL RELAY INSTRUCTION 34

4.4.1 LOGIC DIAGRAM FOR MAIN SOURCE 36

4.4.2 LOGIC DIAGRAM FOR SOLAR SOURCE 36

4.4.3 LOGIC DIAGRAM FOR GENERATOR 37

4.5 LADDER DIAGRAM FOR SWITCH OVER 37

4.6 SCREENSHOT OF PLC LOGIC 38

5.2 BLOCK DIAGRAM OF PLC 41

5.4 OPERATION CYCLE IN PLC 43

5.13.3.1 INPUT MODULE 50

5.13.4.1 OUTPUT MODULE 51

5.13.5 OUTPUT INTERFACING CIRCUIT 51

8.1 HARDWARE OF THE PROJECT 58

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LIST OF TABLES

TABLE NO TITLE PAGE NO

1 MEMORY OF PLC 27

2 TRUTHTABLE 35

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CHAPTER 1

INTRODUCTION

Now-a-days in industry life the energy management system is becoming

more expansion due to complex in every unit. Mainly cement, steel and paper

processing unit expansion and updating of machines. The objective of Energy

Management is to achieve and sustained optimum energy utilization throughout the

organization to reduce the energy costs or waste without affecting production and

quality and to minimize the environmental effects. Energy saving is important and

effective at all levels of human organizations in the whole world. Energy

Conservation reduces the energy costs and improves the effectiveness.

An important requirement of electric power distribution systems is the need

for automatic operation. In particular, the rapid and reliable transfer of the system

from one power source to another during certain system events is important in

achieving the reliability goals for such systems and the facility serves. However,

the design of such an automatic transfer system is all–too-often considered “less

important” then many other aspects of the overall power system design.

In existing method, maintaining of auto change over is the toughest job. The

knobs in auto change over gets weaker often, so maintain cost gets high, due to this

power source breakdown makes the whole process often get shutdown. In our

proposed method, the auto changeover is to replace through a latest idea of a load

based auto switching methods. Due to this technique each power source will be

supply to an individual station according to it power consumption.

12

This paper deals with the three sources used to give continuous power supply

to the load without interruption. Here voltage is used as a measuring parameter.

The measured voltage is compared with the actual set voltage in the comparator.

The output of the comparator is given as input signal of the PLC. A PLC of

Siemens 7300 is used. If the comparator output is positive means PLC considered

the input as HIGH otherwise LOW. The program for PLC written by using ladder

logic. The output of plc is given to the relay driver IC, which switches appropriate

relay to maintain uninterrupted supply to the load. The output shall be observed

using a lamp drawing power supply from mains initially. On failure of the mains

supply the load gets supply from the next available sources are solar, generator. If

the solar also fails it switches over to the next available source and so on. Three

LEDS are used to indicate what are the source are available to give the power

supply to the load.

1.1 . PLC COMPARED WITH MICROCONTROLLER SYSTEM

PLCs are well adapted to a range of automation tasks. These are typically

industrial processes in manufacturing where the cost of developing and

maintaining the automation system is high relative to the total cost of the

automation, and where changes to the system would be expected during its

operational life. PLCs contain input and output devices compatible with industrial

pilot devices and controls; little electrical design is required, and the design

problem centers on expressing the desired sequence of operations. PLC

applications are typically highly customized systems, so the cost of a packaged

PLC is low compared to the cost of a specific custom-built controller design. On

the other hand, in the case of mass-produced goods, customized control systems

are economical. This is due to the lower cost of the components, which can be

13

optimally chosen instead of a "generic" solution, and where the non-recurring

engineering charges are spread over thousands or millions of units.

For high volume or very simple fixed automation tasks, different techniques

are used. For example, a consumer dishwasher would be controlled by an

electromechanical cam timer costing only a few dollars in production quantities.

A microcontroller-based design would be appropriate where hundreds or

thousands of units will be produced and so the development cost (design of power

supplies, input/output hardware, and necessary testing and certification) can be

spread over many sales, and where the end-user would not need to alter the control.

Automotive applications are an example; millions of units are built each year, and

very few end-users alter the programming of these controllers. However, some

specialty vehicles such as transit buses economically use PLCs instead of custom-

designed controls, because the volumes are low and the development cost would be

uneconomical.

Very complex process control, such as used in the chemical industry, may

require algorithms and performance beyond the capability of even high-

performance PLCs. Very high-speed or precision controls may also require

customized solutions; for example, aircraft flight controls. Single-board

computers using semi-customized or fully proprietary hardware may be chosen for

very demanding control applications where the high development and maintenance

cost can be supported. "Soft PLCs" running on desktop-type computers can

14

interface with industrial I/O hardware while executing programs within a version

of commercial operating systems adapted for process control needs.

Programmable controllers are widely used in motion, positioning, and/or

torque control. Some manufacturers produce motion control units to be integrated

with PLC so that G-code (involving a CNC machine) can be used to instruct

machine movements.

PLCs may include logic for single-variable feedback analog control loop,

a proportional, integral, derivative (PID) controller. A PID loop could be used to

control the temperature of a manufacturing process, for example. Historically

PLCs were usually configured with only a few analog control loops; where

processes required hundreds or thousands of loops, a distributed control

system (DCS) would instead be used. As PLCs have become more powerful, the

boundary between DCS and PLC applications has been blurred.

PLCs have similar functionality as remote terminal units. An RTU, however,

usually does not support control algorithms or control loops. As hardware rapidly

becomes more powerful and cheaper, RTUs, PLCs, and DCSs are increasingly

beginning to overlap in responsibilities, and many vendors sell RTUs with PLC-

like features, and vice versa. The industry has standardized on the IEC 61131-

3 functional block language for creating programs to run on RTUs and PLCs,

although nearly all vendors also offer proprietary alternatives and associated

development environments.

15

In recent years "safety" PLCs have started to become popular, either as

standalone models or as functionality and safety-rated hardware added to existing

controller architectures (Allen-Bradley Guardlogix, Siemens F-series etc.). These

differ from conventional PLC types as being suitable for use in safety-critical

applications for which PLCs have traditionally been supplemented with hard-

wired safety relays. For example, a safety PLC might be used to control access to a

robot cell with trapped-key access, or perhaps to manage the shutdown response to

an emergency stop on a conveyor production line. Such PLCs typically have a

restricted regular instruction set augmented with safety-specific instructions

designed to interface with emergency stops, light screens, and so forth. The

flexibility that such systems offer has resulted in rapid growth of demand for these

controllers.

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CHAPTER 2

BLOCK DIAGRAM AND DESCRIPTION

2.1. BLOCK DIAGRAM

Fig 2.1 Block Diagram

2.2. BLOCK DIAGRAM DESCRIPTION

2.2.1. MAIN AND GENSET MEASUREMENT

In this, voltage protection circuit is used to sense the voltage in between the

phase and neutral in 3 phase 4 wire system.

Here 230V supply given to the input of the primary winding of the potential

transformer. The potential transformer is step - down the voltage in (6-0-6V).

P.T

I2

GENSETIN

P.T

I1

SOLARPANEL

-

LOAD BUS

+

-

+

-

LOADBUS

RECTIFIERWITHFILTER

BATTERY

GENSETIN

RELAY

COMPARATOR

SOLARIN

COMPARATOR

RELAY

MAINSIN

+

-

+

MAINSIN

+

RELAY

-

+

RELAY

C

POTENTIALDIVIDER

RELAY

L

+

- RELAY

P

-

-

Q1

+

Q2

RECTIFIERWITHFILTER

I3

COMPARATOR

Q3

17

The stepped down AC 6-0-6V is rectified and filtered by using of this full

wave rectifier and filtering circuits. At this smooth dc low voltage applied across

the variable resistor 10K which is used to provide the variable dc milli voltage.

This voltage is fed to the comparator.

2.2.2. SOLAR PHOTOVOLTAIC ARRAY

The solar photovoltaic array consists of an appropriate number of solar cells

connected in series and or parallel to provide the required current and voltage. The

array is so oriented as to collect the maximum solar radiation throughout the year.

There may be tracking arrays or modules or fixed arrays. A tracking array is

defined as one which is always kept mechanically perpendicular to the sun array

line so that all times it intercepts the maximum isolation. Such arrays must be

physically movable by a suitable prime mover and are generally considerably more

complex than fixed arrays. A fixed array is usually oriented east west and tilted up

at an angle approximately equal to the latitude of the site. Thus the array design

falls into two broad classes:

(I) FLAT PLATE ARRAYS

Where in solar cells are attached with a suitable adhesive to some kind of

substrate structure usually semi rigid to prevent cells being cracked.

18

This technology springs from the space related photovoltaic technology and

many such arrays have been built in various power sizes.

(II) CONCENTRATING ARRAYS

Wherein suitable optics, e.g. Fresnel lenses, parabolic mirrors are combined

with photovoltaic cells in an array fashion. This technology is relatively new to

photovoltaic in terms of hardware development and comparatively fewer such

arrays have actually been built.

2.2.3. BATTERY BANK

In most alone PV power systems, storage batteries with charge regulators

have to be incorporated to provide a backup power source during periods of low

solar irradiance and night. Several types of accumulator are available in the market

for use in PV power systems. The main requirements to be met by an accumulator

for solar power system are,

Ability to withstand several charge/discharge cycle.

A low self discharge rate

Little or no need for maintenance

The capacity of a battery is the total amount of electricity that can be drawn

from a fully charged battery at a fixed discharge rate and electrolyte temperature

until the voltage falls to a specified minimum. It is expressed in ampere hour. The

capacity of the battery also depends upon the temperature and age of battery.

19

The batteries in most PV systems are of lead acid type consisting of one or

more 2v cells. Each cell has a positive plate of lead peroxide and a negative plate

of sponge lead. The electrolyte is dilute sulphuric acid. During discharging when

current is drawn from it, the material of both plates’ changes to lead sulphate and

water content in the electrolyte increases thereby reducing its specific gravity.

When the battery is charged by passing electric current through it in the

opposite direction, the reverse chemical reaction takes place. The cell voltages are

typically 2.4v and 1.9v for fully charged and deeply discharged battery

respectively. Lead acid batteries self discharge slowly when not in use.

2.2.4. PROGRAMMING LOGIC CONTROLLER

The signals from the fault detecting circuits will be connected to the PLC

controller. Here are using Siemens PLC. Here we are using SIEMENS make

LOGO model P.L.C., which is having 8 inputs and 4 outputs.

2.2.5. DRIVER CIRCUIT

The relay section contains relays and ULN2003driver. The microcontroller

gives a logic high output when required and this logic high output has to drive the

relay. The ULN2003 is comprised of seven high voltage, high current NPN

Darlington transistor pairs. All units feature common emitter, open collector

outputs. To maximize their effectiveness, these units contain suppression diodes

20

for inductive loads and appropriate emitter base resistors for leakage. The

ULN2003 has a series base resistor to each Darlington pair, thus allowing

operation directly with TTL or CMOS operating at supply voltages of 5.0V.

The ULN2003 offers solutions to a great many interface needs, including

solenoids, relays, lamps, small motors, and LEDs. Applications requiring sink

currents beyond the capability of a single output may be accommodated by

paralleling the outputs.

2.2.6. RELAY

Relays are switching devices. Switching devices are the heart of

industrial electronic systems. When a relay is energized or activated,

contacts are made or broken. They are used to control ac or dc power.

Electromagnetic relays are forms of electromagnets in which the coil

current produces a magnetic effect. It pulls or pushes flat soft iron

armatures or strips carrying relay contacts. Several relay contact can be

operated to get several possible ON/OFF combinations.

2.2.7. POWER SUPPLY

A power supply circuit is very essential in any project. This power supply

circuit is designed to get regulated output DC voltage. The 15-0-15 volt

transformer, step down the main voltage (230v) into15 volts. The secondary

voltage of transformer is rectified using bridge rectifier. The rectified

unidirectional DC is smoothed by 1000mf filter capacitor. The smooth DC is then

21

fed to the three terminal +ve regulator called 7812 to get 12v DC supply. -ve

regulator called 7912 to get -12v DC supply. The power supply section is for

supplying voltages to the entire circuit.

22

CHAPTER 3

3. HARDWARE DESCRIPTION

3.1. CIRCUIT DIAGRAM

Fig 3.1Circuit diagram

3.2. CIRCUIT DIAGRAM DESCRIPTION

3.2.1. DUAL POWER SUPPLY

It is an electronics unit. This is used to give regulated power to any

electronics system.

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Fig 3.2.1 Dual power supply

3.2.2. CIRCUIT DESCRIPTION

This power supply circuit is designed to get regulated output dc voltage. The

9 volt transformer, step down the main voltage (230v) into 9 volts. The secondary

voltage of transformer is rectified using bridge rectifier. The rectified

unidirectional dc is smoothed by 1000mf filter capacitor. The smooth dc is then fed

to the three terminal +ve regulator called 7805 to get 5v dc supply.

3.2.3. CIRCUIT OPERATIONS

The mains voltage ac 230v is step down to 9 volt, using 9v step down

transformer. The low value secondary voltage is fed to the rectifier is formed using

four no. of IN4007. For first half cycle, diodes d1 & d2 come to action and next

7812

1

2

3

7912

IN4007*4

0.1MF

+

1000MF/25V

0-230V AC

STEP DOWN TRANSFORMER

15V

GREEN

+

100MF/25V

+12V

GND

3

2K2

2

1

0V

15V+

100MF/25V

REDPH

0.1MF

+

1000MF/25V

NE

-12V

2K2

24

half cycle diode d3 & d4 come to action, finally unidirectional dc supply is fed to

the filter capacitor. The charging & discharging property of capacitor provide pure

smooth dc is nearly peak value of the secondary voltage. The pure dc supply is fed

to regulator IC’s input terminal. Due to the regulator action, finally, regulated 5

volts is available at output terminals.

Fig 3.2.3 7812 Regulator IC pin

Fig 3.2.4 7912 Regulator IC pin

3.3. POTENTIAL TRANSFORMER CIRCUIT

Potential transformers are used to operate voltmeters, the potential coils of

watt meters and relays from high voltage lines. The primary winding of the

transformer is connected across the line carrying the voltage to be measured and

the voltage circuit is connected across the secondary winding.

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Fig 3.3 Potential Transformer

The design of a potential transformer is quite similar to that of a power

transformer but the loading of a potential transformer is always small, some times

only a few voltage ampere. The secondary winding is designed so that a voltage of

9 to 12V is delivered to the instrument load. The normal secondary voltage rating

is 12V.

3.4. OPERATIONAL AMPLIFIER

An operational amplifier is a multistage, direct-coupled high-gain amplifier

to which negative feedback is added, to control its overall response

characteristics.

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Now Op-amp is used for a variety of applications, such as DC and AC signal

amplification, oscillators, comparators, voltage regulators and many others.

3.4.1. SYMBOLIC DIAGRAM OF OPERATIONAL AMPLIFIER

Figure shows the block diagram of a typical op-amp. There are two inputs,

labeled as V1 and V2. The input voltage is V1 and V2 with respect to the ground.

The output voltage is Vo with respect to ground. The output is given by,

Fig 3.4.1 Symbolic diagram of operational amplifier

3.4.2. INVERTING MODE

Where AV is the voltage gain of the op-amp. AV is assumed to be negative

for the differential input V1-V2. It is seen that Vo is proportional to negative of V1.

27

Hence, a signal applied as V1 is inverted (180o phase change) at the output. So V1

is called the inverting input. It is denoted by a negative sign at the terminal in the

block diagram.

Fig 3.4.2 Inverting mode

3.4.3. NON-INVERTING MODE

Any signal applied as the other input voltage V2 produce an output

proportional to V2 and is in phase with it. Hence V2 is called the Non-inverting

input. It is denoted by ‘plus’ sign at the terminal in the block diagram.

Fig 3.4.3 Non-inverting mode

There is one lead common to both the inputs and the output. This is the

ground lead. Since the ground lead is common to all parts of the circuit, it is often

not shown in diagrams. For using the op-amp, it must be connected to a dual

power supply (having +Vcc and –Vcc with respect to common earth).

28

The function of the op-amp described above can be summarized as follows:

If differential input Vid = (V1 – V2) is positive; the output is negative (VO).

If differential input Vid = (V1 – V2) is negative; the output is positive (+VO).

3.4.4. IC-741 PIN DETAILS

Fig 3.4.4 IC-741 pin diagram

The op-amp symbol is a triangle that points in the direction of the signal flow.

This component has a Part Identification Number (PIN) placed within the

triangular symbol. Of the different types of op-amps produced, op-amp IC 741

type is widely used. It is available in 8 pin Dual-In-Line Package (DIP) or in TO-

style package. The pin configuration of the 8 pin (DIP) package is shown in

figure.

29

The operational amplifier needs a dual symmetrical power supply (+Vcc and –

Vcc) with the center tap of the power transformer secondary earthed. This earth is

used as the common earth for all voltage sources in the circuit.

The important technical parameters of IC 741 are given below:

Supply voltage : 5 to 18V

Input resistance : Zin = 2 Mega ohms

Output resistance : Zo = 75 ohms

Voltage gain : Av = 200,000 (106 dB)

Small signal band width : 1 Megahertz

Power consumption : 50-85 mW

Output short-circuit current : 25mA

Slew rate : 0.5 V/ s

3.4.5. ADVANTAGES OF OPERATIONAL AMPLIFIER

For a given operation, OP-Amps have the following advantages over

conventional amplifier.

Smaller size

Higher reliability of operation

Reduced cost

Low offset voltage and current

30

High versatility

More flexibility

3.5. ULN DRIVER

3.5.1. HIGH CURRENT/VOLTAGE DARLINGTON DRIVERS

The ULN2003 is comprised of seven high voltage, high current NPN

Darlington transistor pairs. All units feature common emitter, open collector

outputs. To maximize their effectiveness, these units contain suppression diodes

for inductive loads and appropriate emitter base resistors for leakage. The

ULN2003 has a series base resistor to each Darlington pair, thus allowing

operation directly with TTL or CMOS operating at supply voltages of 5.0V.

The ULN2003 offers solutions to a great many interface needs, including

solenoids, relays, lamps, small motors, and LEDs. Applications requiring sink

currents beyond the capability of a single output may be accommodated by

paralleling the outputs.

31

3.5.2. ULN 2003 PIN DIAGRAM

Fig 3.5.2 ULN 2003 pin diagram

3.5.3. FEATURES OF ULN DRIVER

Seven high gain Darlington pairs

High output voltage (VCE = 50V)

High output current (IC = 350 mA)

TTL, PMOS, CMOS compatible

Suppression diodes for inductive loads

Extended temperature range

3.6. TRANSISTOR AS A SWITCH

When a transistor is used as driver circuit, it can withstand for high

frequency signal. So a NPN transistor is used here as a driver circuit. When

32

a transistor is used as a switch it is usually required to be brought

alternatively in the saturation and in the cut-off conditions.

When in saturation condition, it should carry heavy current so that the

voltage drop across it is as near to zero as possible and when in cutoff

condition, it should carry almost no current so that it may be considered to

be an open switch. It is found that the transistor does not respond

instantaneously but takes a certain definite, though quite small, time in

making a transition from one state to the other.

3.7. RELAY

Relays are switching devices. Switching devices are the heart of

industrial electronic systems. When a relay is energized or activated,

contacts are made or broken. They are used to control ac or dc power. They

are used to control the sequence of events in the operation of a system such

as an electronic heater, counter, welding circuits, X-ray equipment,

measuring systems, alarm systems and telephony. Electromagnetic relays

are forms of electromagnets in which the coil current produces a magnetic

effect. It pulls or pushes flat soft iron armatures or strips carrying relay

contacts. Several relay contact can be operated to get several possible

ON/OFF combinations.

33

3.7.1. OPERATION OF ELECTROMAGNETIC RELAY

Relays are usually dc operated. When dc is passed to the coil, the

core gets magnetized. The iron armature towards the core contacts 1 and 2

open and contacts 2 and 3 close. When coil current is stopped, the

attraction is not there and hence the spring tension brings 1 and 2 to closed

position, opening the other set 2 and 3.

Fig 3.7.1 operation of electromagnetic relay

Fig 3.7.1.1 Contact of electromagnetic relay

34

3.7.2. RELAY DRIVER CIRCUIT

Fig 3.7.2 Relay diver circuit

3.8. VOLTAGE MEASUREMENT

In this, voltage protection circuit is used to sense the voltage in between the

phase and neutral in 3 phase 4 wire system.

Here 230V supply given to the input of the primary winding of the potential

transformer. The potential transformer is step - down the voltage in (6-0-6V).

The stepped down AC 6-0-6V is rectified and filtered by using of this full

wave rectifier and filtering circuits. At this smooth dc low voltage applied across

the variable resistor 10K which is used to provide the variable dc milli voltage.

This voltage is fed to the comparator.

35

Fig 3.8 Voltage measurement circuit

3.9. VOLTAGE COMPARATOR

The input from the voltage measurement is given to inverting terminal and

the set value of voltage is given to non-inverting terminal. This can be set by using

the variable resistance 10K. At normal 230v, the voltage at the inverting terminal

is more than reference, so –V sat is the output from op amp. When the voltage

lowers than the specified limit, inverting terminal voltage is below the reference

voltage of non-inverting terminal. Hence the op amp output is +V sat indicating the

fault occurrence and the transistor conducts and the signal given to PLC.

Fig 3.9 Voltage comparator

10KO/P

~ ~

+-

IN4007*4BRIDGE

+

220M

FD

/25V

(0-230V)

2K7

TRANSFORMER

6V

4K7+

-

741

3

26

74

1K

-5V 4K7

+5V

1K

10K

I/P

HIGH

FROM VOLTAGEMEAUSREMENT

HIGH SET

BC547

36

CHAPTER 4

SOFTWARE DESCRIPTION

4.1. FUNDAMENTALS OF LOGIC

The PLC like all digital equipments operates on binary principle.

4.1.1. HARD-WIRED LOGIC VS PROGRAMMED LOGIC

The term hard-wired refer to logic control functions that are determined by

the way devices are connected. Hard-wired logic can be diagram. The logic

ladder diagram for the given relay ladder diagram is illustrated in the figure. The

instructions used are the relay equivalent of normally open (NO) and normally

closed (NC) contacts and coils. A rung is the content symbology required to

control the output, conventionally on output per rung is allowed. Because the PLC

uses logic diagrams, the conversion from existing relay logic to programmed logic

is simple. Each rung is a combination of input conditions connected from left to

right with the symbol that represents the output at the far right. The symbols that

represent the inputs are connected in series, parallel or some combination to obtain

the desired logic.

Fig 4.1.1 Ladder diagram

37

4.2. BASICS OF PLC PROGRAMMING

4.2.1. PROCESSOR MEMORY ORGANISATION

The term processor memory organization refers to how certain areas of

memory is given PLC are used.

The figure shown above is an illustration of memory organization known as

a memory map. The memory space can be divided into two broad categories: the

user program and the data table.

DATA TABLE

MAIN

PROGRAM USER PROGRAM

SUBROUTINE

MESSAGE STORAGE AREA

Table 1 Memory of plc

The user program is where the programmed logic ladder diagram is entered

stored. It contains the logic that controls the machine operation. This logic

consists of instruction that is programmed in a ladder logic format. Most

instructions required one word of memory.

The data table stores the information needed to carry out the user program.

Contents of the data table can be divided into two categories. Status data and

number of codes. Status is ON/OFF type of information represented by 1’s and 0’s

38

stored in unique bit locations. Number or code information is represented by

groups of bits which are stored in unique byte or word locations.

Fig 4.2.1 Life cycle

The data table can be divided into the following three sections according to

the type of information to be remembered: input image table, output image table,

and counter and timer storage. The input image stores the status of digital inputs

which are connected to input interface circuits. The output image table is an array

of bits that controls the status of digital output devices which are connected to

output interface circuits.

4.2.2. PROGRAM SCAN

During each operation cycle, the processor read all the inputs, takes these

values and according to the user program energies the outputs. This process is

known as scan. The PLC scan time specifications indicate how fast the controller

can react to change in inputs. The scan time varies from 1ms to 100ms. If a

controller has to react to an input signal that changes states twice during the scan

time. It is possible that the PLC will never be able to detect this change.

39

The scan is normally a continuous sequential process of reading the status of

inputs, evaluating the control logic and updating the outputs. The figure below

illustrates this process. When the input devices connected to address 101-14 is

closed, the input module circuitry serves a voltage and a1 (ON) conditions is

entered into the input image table bit 101 – 14. During the program scan the

processor examines bit 101-14 is the rung is said to be true. The processor then

sets the output image table bit 044-0 t1. The processor turns on output 001-04

during the next I/O scan and the output device wired to this terminal becomes

energize. This process is repeated as long as the processor is in the RUN mode. If

the input device were to be false. The processor would then set the output image

table bit 001-40 to 0, causing the output device to turn off.

4.3. PLC PROGRAMMING LANGUAGE

The term PLC programming language refers to the method by which the

user communicates information to the PLC. The two most common language

structures are ladder diagram and Boolean language.

4.3.1. RELAY – TYPE INSTRUCTION

The ladder diagram language is basically a symbolic set of instructions used

to create the controller program. Because this instruction set is composed of

contact symbols, ladder diagram language is also referred to as contact symbology.

40

Representation of contacts and coils are the basic of the logic ladder diagram

instruction set. The following are the basic symbols used to translate relay control

logic to contact symbolic logic.

4.3.1.1. SYMBOL DESCRIPTION

Examine ON instruction. This represents any input to control logic. The

input can be switch, push button etc. It is linked to a status bit in the data

table. The status bit will be either 1 (ON) or 0 (OFF). The status bit is

examined for an ON condition. If the status bit is 1 (ON) then the

instruction is TRUE. If the status bit is 0 (OFF) then the instruction is

FALSE.

Examine OFF instruction. Typically represents any input to the control

logic. The input can be connected switch, push button, etc.; it is linked to a

status bit in the data table. The status bit is examined for an OFF condition.

If the status bit is 0 (OFF) then the instruction is TRUE. If the status bit is 1

(ON) then the instruction is FALSE.

Output energizes. Represents any output that is controlled by some

combination of input logic. An output can be connected device or an

internal; output. If any left-to-right path of input conditions is TRUE, the

output is energized. The status bit of the addressed output energize

instruction is set 1 (ON) when the rung is true else reset to 0.

The main function of the logic ladder diagram program is to control outputs

based on input conditions. This is accomplished with a ladder rung. A rung

consists of a set of input, conditions, represented by contact instructions and an

41

output instruction at the end of the rung represented by the coil symbol. Each

contact or coil symbol is referenced with an added number that identifies what is

being evaluated and what is being controlled. For an output to be activated, at least

one left-to-right path of contacts must be closed. A complete closed path is referred

to as having logic continuity. When logic continuity exists in at least one path, the

rung condition is said t be TRUE. The rung condition is FALSE if no path has

continuity.

Fig 4.3.1.1 Symbol description

4.3.2. INSTRUCTION ADDRESSING

The entry of a relay type of instruction is completed when an address

number is assigned to it. This number indicated what PLC input is connected to

what input device and what PLC output will drive what output devices. These

addresses can be represented in decimal, octal or hexa decimal. The figure

illustrated a typical addressing format.

42

The address identifies the function of an instruction and looks it to particular

status bit in the data table portion of the memory. The figure shows the structure

of a 16 bit word and its assigned bit values. The breakdown of this word and its

addressing format are in decimal.

Fig 4.3.2 Instruction Address

4.3.3. BRANCH INSTRUCTION

Branch instruction is used to create parallel paths of inputs condition

instructions. This allows more than one combination of input conditions

instructions (OR logic) to establish logic continuity in a rung.

The figure illustrated simple branching instructions. Te rung will be true if

either instruction 110/00 or 110/01 is true. A branch start instructions is used to

begin each parallel logic branch. A single branch close instruction is used to close

the parallel branch. A maximum of seven parallel lines and ten series contacts per

rung is possible. Also a PLC will no allow programming of vertical contacts.

43

Fig 4.3.3 Batch instruction

4.3.4. INTERNAL RELAY INSTRUCTION

Certain area of the memory is allocated for internal storage bits. These

storage bits are also called internal outputs, internal coils, internal control relays or

just internals. An internal output does not directly control an output device. An

internal control relay can be used when a circuit requires more series contacts then

the rung allows.

The figure shows the circuit that allows for only seven series contacts when

twelve are actually required for the programmed logic. To solve this problem, the

contacts are split into two rungs as shown in figure. The first rung contains the

seven of the required contacts and is programmed to an internal relay. The address

of the internal relay 033, in example would also be address of the first examine.

On contact on the second rung. The remaining five contacts are programmed,

followed by the discrete output 009. When the first seven contact close, internal

outputs 003 would be set to 1. This would make the examine for ON contacts 033

44

in rung 2 as true. If the other five contacts is rung 2 closed, the rung would be true

and the discrete output 009 would be turned on.

Closed, the rung would be true and the discrete output 009 would be turned

ON.

Fig 4.3.4 Internal relay instruction

45

4.4. TRUTH TABLE

INPUT OUTPUT

MAIN SOLAR GEN SET MAIN SOLAR GEN SET

0 0 0 0 0 0

1 0 0 1 0 0

1 1 0 1 0 0

1 0 1 1 0 0

1 1 1 1 0 0

0 1 0 0 1 0

0 1 1 0 1 0

0 0 1 0 0 1

Table 2 Truth table

46

4.4.1. LOGIC DIAGRAM FOR MAIN SOURCE ON

Fig 4.4.1 Logic diagram for main source

4.4.2. LOGIC DIAGRAM FOR SOLAR ON

Fig 4.4.2 Logic diagram for solar source

47

4.4.3. LOGIC DIAGRAM FOR GENERATOR ON

Fig 4.4.3 Logic diagram for generator

4.5. LADDER DIAGRAM FOR SWITCH OVER

Fig 4.5 Ladder diagram for switch over

48

4.6. PLC LOGIC

Fig 4.6 Screenshot of plc logic

49

CHAPTER 5

PROGRAMMABLE LOGIC CONTROLLER (PLC)

A PLC or programmable logic controller is a digital computer used for

automation of electromechanical process, such as control of machinery on factory

assembly lines, light fixtures.

PLC are used in industries and machineries. Unlike general purpose

computers, the PLC is design for multiple inputs and outputs arrangements,

extended temperature ranges, immunity to electrical noise, and resistance to vibrate

and impact.

Programs are control machine operation is usually stored in battery-backed-

up or non-volatile memory. A PLC is an example of a "hard" real-time system

since output results must be produced in response to input conditions within a

limited period of time, otherwise unintended operation will be result occur. PLC is

an assembly of solid-state element designed to make logical and sequential

decisions and provide outputs. Programmable logic controller has eliminated much

of the hardwiring and associated with conventional relay control circuits.

5.1. HISTORY

Before the plc control sequencing and safety interlock logic for

manufacturing automobiles was composed relays com timers drum sequencers, and

dedicated closed loop controller. Since these could number in the hundreds and

even in the thousands, the process for updating such facilitates for yearly model

50

change-over was very time consuming and expensive ,as electrician needed to

individually rewire relays to change the logic.

In 1968 GM Hydro-Matic (automatic transmission division of general

motors) issued a request for proposal for an electronic replacement for hardwired

relay system based on white paper written by Er. Edward R. Clark.

The first PLC designed at 084 because it was Bedford Associates, eighty

fourth projects, was the result. This company is dedicated to developing,

manufacturing, selling, and servicing the new product: Modicon, one of the people

who worked on that project was DICK MORLEY, who is considered to be the

FATHER OF PLC. The Modicon brand was sold in 1997 to GOULD

ELECTRONICS, and later acquired by German company AEG and then by French

SCHNEIDER ELECTRIC, the current owner.

5.2. DEVELOPMENT

Early PLCs were designed to replace relay logic systems. These PLCs were

programmed in “ladder logic”, which strongly resembles a schematic diagram of

relay logic. This program notation was chosen to reduce training demands for the

existing technique. Other early PLCs used a form of instruction list programming,

based on a stack-based logic solver.

Modern PLCs can be programmed in a variety of ways, from the relay

derived ladder logic to programming language such as specially adaptes dialect of

51

BASIC and C. Another method is STATE LOGIC a VERY HIGH LEVEL

PROGRAMMING LANGUAGE designed to program PLCs based on STATE

TRASITION DIAGRAMS.

Fig 5.2 Block diagram of plc

5.3. TYPES OF PLC

Allen Bradley PLCs (AB)

ABB PLCs (Asea Brown Boveri)

Siemens PLCs

Omron PLCs

Mitsubishi PLCs

Hitachi PLCs

Delta PLCs

General Electric (GE) PLCs

Honeywell PLCs

52

Modicon PLCs

Schneider Electric PLCs

Bosch PLCs

It emphasis convertibility without have complete rebuild the protection lines.

Needs for manufacturing industries to increase product widely

In 1960’s PLC were introduced. The primary reason for designing such a

device was eliminating the large cost involved in repairing complicated relay based

machine control systems.

The MODICON 084 was the world’s first PLC as commercial product to the

Major US car manufacturer. {at that time all others used PC based systems}

1973 --- AB PLC with COM

1980 ---Small size with COM

1990 --- PC based control & SCADA

5.4. STEPS FOR PLC OPERATION

Step 1: Input Scan

It detects the state of all input devices and connected to the PLC.

Step 2: Program Scan

Program logic will be created and executed.

53

Step 3: Output Scan

Energizes / de-energize in all of the output devices that are connected to the

programmable logic controller.

Step 4: Housekeeping

This step includes the communications with programming terminals, internal

diagnostics, etc...

.

Fig 5.4 Operation cycle in plc

5.5. PROGRAMMING

Early PLCs, upto the mid-1980s,were programmed using proprietary

programming panels or special-purpose programming terminals, which often had

dedicated function keys representing the various logical elements of PLC

programs.

54

Programs were stored on cassette tape catridges. Facilities for printing and

documentation were minimal due to lack of memory capacity. The very oldest

PLCs used non-volatile magnetic core memory.

More recently, PLCs are programmed using application software on

personal computers.

Which now represent the logic in graphic from instead of character symbols.

The computer is connected to the PLC through Ethernet, RS-232, RS485 or RS-

422. The programming software allows entry and editing of the ladder-style logic.

Generally the software provides function for debugging and troubleshooting the

PLC software.

5.6. FUNCTIONALITY

The functionality of the PLC has evolved over the years to include

sequential relay control, motion control, process control, distributed control

system, and networking. The data handling, storage, processing power, and

communication capabilities of some modern PLCs are approximately equivalent

to desktop computers. PLC-like programming combined with remote I/O

hardware, allow a general-purpose desktop computer to overlap some PLCs in

certain applications. Desktop computer controllers have not been generally

accepted in heavy industry because the desktop computers run on less stable

operating systems than do PLCs, and because the desktop computer hardware is

typically not designed to the same levels of tolerance to temperature, humidity,

55

vibration, and longevity as the processors used in PLCs. Operating systems such as

Windows do not lend themselves to deterministic logic execution, with the result

that the controller may not always respond to changes of input status with the

consistency in timing expected from PLCs. Desktop logic applications find use in

less critical situations, such as laboratory automation and use in small facilities

where the application is less demanding and critical, because they are generally

much less expensive than PLCs.

5.7. PROGRAMMABLE LOGIC RELAY

These small devices are typically made in a common physical size and shape

by several manufacturers, and branded by the makers of larger PLCs to fill out

their low end product range. Popular names include PICO Controller, NANO PLC,

and other names implying very small controllers. Most of these have 8 to 12

discrete inputs, 4 to 8 discrete outputs, and up to 2 analog inputs. Size is usually

about 4" wide, 3" high, and 3" deep. Most such devices include a tiny postage-

stamp-sized LCD screen for viewing simplified ladder logic (only a very small

portion of the program being visible at a given time) and status of I/O points, and

typically these screens are accompanied by a 4-way rocker push-button plus four

more separate push-buttons, similar to the key buttons on a VCR remote control,

and used to navigate and edit the logic. Most have a small plug for connecting via

RS-232 or RS-485 to a personal computer so that programmers can use simple

Windows applications for programming instead of being forced to use the tiny

LCD and push-button set for this purpose. Unlike regular PLCs that are usually

modular and greatly expandable, the PLRs are usually not modular or expandable,

56

but their price can be two orders of magnitude less than a PLC, and they still offer

robust design and deterministic execution of the logics.

5.8. SCAN TIME

A PLC program is generally executed repeatedly as long as the controlled

system is running. The status of physical input points is copied to an area of

memory accessible to the processor, sometimes called the "I/O Image Table". The

program is then run from its first instruction rung down to the last rung. It takes

some time for the processor of the PLC to evaluate all the rungs and update the I/O

image table with the status of outputs. This scan time may be a few milliseconds

for a small program or on a fast processor, but older PLCs running very large

programs could take much longer (say, up to 100 ms) to execute the program. If

the scan time were too long, the response of the PLC to process conditions would

be too slow to be useful.

As PLCs became more advanced, methods were developed to change the

sequence of ladder execution, and subroutines were implemented. This simplified

programming could be used to save scan time for high-speed processes.

5.9. SYSTEM SCALE

A small PLC will have a fixed number of connections built in for inputs and

outputs. Typically, expansions are available if the base model has insufficient I/O.

57

Modular PLCs have a chassis (also called a rack) into which are placed

modules with different functions. The processor and selection of I/O modules are

customized for the particular application. Several racks can be administered by a

single processor, and may have thousands of inputs and outputs. Either a special

high speed serial I/O link or comparable communication method is used so that

racks can be distributed away from the processor, reducing the wiring costs for

large plants. Options are also available to mount I/O points directly to the machine

and utilize quick disconnecting cables to sensors and valves, saving time for wiring

and replacing components.

5.10. USER INTERFACE

PLCs may need to interact with people for the purpose of configuration,

alarm reporting, or everyday control. A human-machine interface (HMI) is

employed for this purpose. HMIs are also referred to as man-machine interfaces

(MMIs) and graphical user interfaces (GUIs). A simple system may use buttons

and lights to interact with the user. Text displays are available as well as graphical

touch screens. More complex systems use programming and monitoring software

installed on a computer, with the PLC connected via a communication interface.

5.11. COMMUNICATIONS

PLCs have built-in communications ports, usually 9-pin RS-232, RS-

422, RS-485, Ethernet. Various protocols are usually included. Many of these

protocols are vendor specific.

58

Most modern PLCs can communicate over a network to some other system,

such as a computer running a SCADA (Supervisory Control And Data Acquisition)

system or web browser.

PLCs used in larger I/O systems may have peer-to-peer (P2P)

communication between processors. This allows separate parts of a complex

process to have individual control while allowing the subsystems to co-ordinate

over the communication link. These communication links are also often used

for HMI devices such as keypads or PC-type workstations.

5.12. DISCRETE AND ANALOG SIGNALS

Discrete signals behave as binary switches, yielding simply an On or Off

signal (1 or 0, True or False, respectively). Push buttons, limit switches,

and photoelectric sensors are examples of devices providing a discrete signal.

Discrete signals are sent using either voltage or current, where a specific range is

designated as On and another as Off. For example, a PLC might use 24 V DC I/O,

with values above 22 V DC representing On, values below 2VDC

representing Off, and intermediate values undefined. Initially, PLCs had only

discrete I/O.

Analog signals are like volume controls, with a range of values between zero

and full-scale. These are typically interpreted as integer values (counts) by the

PLC, with various ranges of accuracy depending on the device and the number of

bits available to store the data. As PLCs typically use 16-bit signed binary

processors, the integer values are limited between -32,768 and +32,767. Pressure,

59

temperature, flow, and weight are often represented by analog signals. Analog

signals can use voltage or current with a magnitude proportional to the value of the

process signal. For example, an analog 0 to 10 V or 4-20 mA input would

be converted into an integer value of 0 to 32767.

Current inputs are less sensitive to electrical noise (e.g. from welders or

electric motor starts) than voltage inputs.

5.13. PLC HARDWARE COMPONENTS

5.13.1. I/O SECTION

The input and output interface modules consist of I/O rack and individual

I/O modules. Input interface accept signals from the machine and convert

controller signals into external signals used to control the machine or process.

5.13.2. DISCRETE I/O MODULES

The most common type of I/O interface module is the discrete type. This

type of interface connects field input devices of the On/Off nature such as selector

switches, push buttons and limit switches. Likewise, output control is limited to

device such as lights, small motors, solenoids and motor starters the require simple

ON/OFF switching.

Each discrete I/O module is powered by some field supply voltage source.

Common ratings for discrete I/O interface modules

INPUT INTERFACE - 230V AC

OUTPUT INTERFACE - Relay

60

5.13.3. CIRCUIT FOR INPUT INTERFACE MODULE

5.13.3.1. BLOCK DIAGRAM OF INPUT MODULE

Fig 5.13.3.1 Block diagram of input interface module

The input circuit is composed of two basic sections: the power section and

the logic section. The power and logic sections are normally coupled together with

a circuit which electrically separates the two.

When the push button is closed, 120V ac is applied to the bridge rectifier

through resistors R1 and R2. This produces a low level direct voltage, which is

applied across the LED of the optical isolator. Zener diode voltage rating sets the

minimum level of voltage that can be detected. When light from the LED strikes

the photo-transistor it switches into conduction and the status of the push button is

communicated in logic or low level dc voltage from the logic circuits but also

prevents damage to the processor due to line voltage transients. Optical isolation

also helps to reduce the effect of electrical noise which can cause erratic operation

of the processor coupling and isolation can also be accomplished by use of the

pulse transformer.

61

5.13.4. CIRCUIT FOR OUTPUT INTERFACE MODULE

5.13.4.1 BLOCK DIAGRAM OF OUTPUT MODULE

Fig 5.13.4.1 Block diagram of output module

It is composed to two basic sections the power section and the logic sections,

coupled by an isolation circuit.

5.13.5. OUTPUT INTERFACING CIRCUIT

Fig 5.13.5 Output interfacing circuit

62

The processor set the output state according to the logic operations. When

the processor call for an output, a voltage is applied across the LED of the isolator.

The LED then emits light, which switches the phototransistor into conduction. This

in turn switches on the trace into conduction which or the lamp. Since the triac

conducts in either direction, the output to the lamp is alternating current. The triac

rather than having ON and OFF states, actually has LOW and HIGH resistance

levels. In it’s OFF (High resistance) state, a small leakage current of a few mill

amperes still flows through the triac. The output interface is provided with LEDs

that indicated the status of each output.

5.13.6. ANALOG I/O MODULE

The analog I/O module contains the circuitry necessary to accept analog

voltage or current signals from analog field devices. These inputs are converted

from an analog or digital value by an analog-to-digital converter circuit. The

converted value, which is proportional to the analog signal, is expressed as 12 bit

binary or as a three digit Binary Coded Decimal (BCD) for use by the processor.

Analog input sensing devices include the following: Temperature light speed

pressure and position transducers.

The analog output interface modules receive from the processor digital data,

which is converted into a proportional voltage or current to control an analog field

device. The digital data is passed through a digital-to-analog converter circuit to

produce the necessary analog form. Analog output devices include the following:

Small motors, valves, analog meters and seven segment displays.

63

5.13.7. I/O SPECIFICATIONS

Manufactures specifications provide much information about how an

interface device is correctly and safely used.

The specifications place certain limitations not only on the module. But also

on the field equipment that it can operate. Some typical manufacturers I/O

specifications are sated below. Nominal input voltage, nominal current per input,

ambient temperature rating, nominal output voltage, etc.

5.13.8. MEMORY DESIGN

Memory is where the control plan or program is held or stored the controller.

The information stored in the memory relates to how the input and output data

should be processed. The complexity of the program determines the amount of

memory required. Memory can either be of the volatile or non-volatile types.

Today’s PLC makes use of many different types of volatile or non-volatile

memory devices. Some of the memory types are listed below: Read-only Memory

(ROM), Random Access Memory (RAM), Programmable Read Only Memory

(PROM), Erasable Programmable Read-only Memory (EPROM), Electrically

Erasable Programmable Read-only Memory (EEPROM), Magnetic Core Memory.

64

CHAPTER 6

APPLICATION AND FEATURES OF PLC

6.1. APPLICATION OF PROGRAMMABLE LOGIC CONTROL

PLC have wide range of industrial applications

Process industry

Automotive industry

Energy monitoring and load shedding

Oil and gas industry

Petro-chemical industry

Water treatment plant

In batch process savings are developed principally from reduced cycle time

and scheduling. Cycle automation provides rigid control enforcement to eliminate

human errors and to minimize manual interventions. Increased efficiency in

scheduling is to be expected with maximum utilization of equipment and reduction

of fluctuating demands on critical equipment.

In large process plants PLCs are being increasingly used for automatic start

up and shutdown of critical equipments. A PLC ensures that an equipment can not

be started unless all the permissive conditions for safe start have been established.

65

It also monitors the conditions necessary for safe running of the equipment and trip

the equipment whenever any abnormality in the system is detected.

The PLC can be programmed to function as an energy management system

for boiler control for maximum efficiency and safety. In the burner management

system it can be used to control the process of purging, pilot light off, flame safety

checks, main burner light off and valve switching for changeover of fuels.

6.2. FEATURES OF PROGRAMMABLE LOGIC CONTROL

PLC control system is that it regards PLC as control key component, utilize

special I/O module to form hardware of control system with a small amount of

measurement and peripheral circuit, to realize control to the whole system through

programming.

6.2.1. HIGH RELIABILITY

Strong anti-interference quality and very high reliability are the most

important features of PLC. In order to make PLC work stably in strong

interferential circumstance. Many techniques are applied in PLC. Software control

instead of relay control mode can decrease faults which are brought about by

original electric contact spot outside working badly. Industrial grade components

made by advance processing technology can resist interferences, and self diagnosis

measures of watchdog circuit for protecting memory can improve performance of

PLC great

66

6.2.2. GOOD FLEXILIBITY

There are several programming languages for PLC including ladder

diagram, SFC, STL, ST and so on. If operator can master only one of programming

languages, he can operate PLC well. Every who want to use PLC has a good

choice. Based on engineering practice, capacity and function can be expanded by

expanding number of module, so PLC has a good flexibility.

6.2.3. QUALITY OF STRONG EASY – OPERATING

It is very easy to edit and modify program for PLC by computer offline or

online. It is very easy to find out where the fault lie by displaying the information

of fault and function of Self Diagnosing Function, and all these make maintenance

and repair for PLC easier. It is very easy to configure PLC because of

modularization, standardization, serialization of PLC.

67

CHAPTER 7

ADVANTAGES AND FUTURE SCOPE OF PLC

7.1. ADVANTAGES OF PROGRAMMABLE LOGIC CONTROL

Less wiring.

Flexibility in programming and reprogramming

Easier and faster to make changes.

Low power consumption

Easy maintenance due to modular assembly

Reduced space

Energy saving

Ease of maintenance /troubleshooting

Remote control capability.

Analog signal handling and close loop control programming

Counter, timer and comparator can be programmed

Ease operator interface due to colourographic and advisory system

introduction

68

CHAPTER 8

RESULTS

Fig 8.1 Hardware of the project

69

CHAPTER 9

CONCLUSION

The project on PROGRAMMABLE LOGIC CONTROL BASED

AUTOMATIC POWER SOURCE CHANGE OVER is working fine, getting

the parameter envisaged during the conceptual stage.

During the design, as well as during the construction, greater care has been

put into avoid hiccups at the final stage. The PCB layouts were prepared with

utmost care to incorporate the circuits in a modular manner. The circuit is made as

simple as to our knowledge. Also components were selected keeping in mind their

availability and cost.

It was a very interesting process of developing the prototype, stage by stage

and testing the same. We have to go through fairly large pages of data related to

the components etc. It was a useful and fulfilling assignment to get the project

completed in time. This gave us a sense of satisfaction and accomplishment.

70

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pp. 115-116, Jan. 2010.

2. Young-Sung Son and Kyeong-Deok Moon, “Home energy management

system based on power line communication,” IEEE Trans.

Consumer Electron., vol. 56, no.3, pp.1380-1386, Aug. 2010.

3. Jinsoo Han, Chang-Sic Choi, Wan-Ki Park, and Ilwoo Lee, “Green home

energy management system through comparison of energy

usage between the same kinds of home appliances,” in Proc.

IEEEInternational Symposium on Consumer Electronics, Singapore, pp. 1-4,

Jun. 2011.

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“Power monitoring and control for electric home appliances

based on power line communication,” in Proc. IEEE

InternationalInstrumentation and Measurement Technology Conference,

British

Columbia, Canada, pp. 2179-2184, May 2008.

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renewable using AC/DC converters as DG power sources,” in

Proc.World Congress Sustainable Technologies, London, UK, pp. 171-

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