PLC

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CHAPTER 1
AUTOMATION
1.1 Introduction to Automation
Automation is the use of control systems such as computers to control industrial
machinery and process, reducing the need for human intervention. In the scope of
industrialization, automation is a step beyond mechanization. Whereas mechanization
provided human operators with machinery to assist them withphysical requirements of
work, automation greatly reduces the need for human sensory and mental requirements as
well. Processes and systems can also be automated.
1.2 Automation Impacts:
1. It increases productivity and reduce cost.
2. It gives emphasis on flexibility and convertibility of manufacturing process. Hence
gives manufacturers the ability to easily switch from manufacturing products.
3. Automation is now often applied primarily to increase quality in the manufacturing
process, where automation can increase quality substantially.
4. Increase the consistency of output.
5. Replacing humans in tasks done in dangerous environments.
1.3 Advantages of Automation:
1. Replacing human operators in tasks that involve hard physical or monotonous work.
2. Performing tasks that are beyond human capabilities of size, weight, endurance etc.
3. Economy improvement: Automation may improve in economy of enterprises, society or
most of humanity.
1.4 Disadvantages of Automation:
1. Technology limits: Current technology is unable to automate all desired tasks.
2. Unpredictable development costs: The research and development cost of automating a
process may exceed the cost saved by the automation itself.
3. High initial cost: The automation of a new product or plant requires a huge initial
investment in comparison with the unit cost of the product.
1.5 Applications
1.5.1 Automated Video Surveillance:
Automated video surveillance monitors people and vehicles in real time within a busy
environment. Existing automated surveillance systems are based on the environment they
are primarily designed to observe, i.e., indoor, outdoor or airborne, the amount of sensors

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that the automated system can handle and the mobility of sensor, i.e., stationary camera vs.
mobile camera. The purpose of a surveillance system is to record properties and
trajectories of objects in a given area, generate warnings or notify designated authority in
case of occurrence of particular events.
1.5.2 Automated Manufacturing:
Automated manufacturing refers to the application of automation to produce things
in the factory way. Most of the advantages of the automation technology has its influence
in the manufacture processes.
The main advantages of automated manufacturing are higher consistency and quality,
reduced lead times, simplified production, reduced handling, improved work flow, and
increased worker morale when a good implementation of the automation is made.
1.5.3 Home Automation:
Home automation designates an emerging practice of increased automation of
household appliances and features in residential dwellings, particularly through electronic
means that allow for things impracticable, overly expensive or simply not possible recent
past decades.
1.5.4 Industrial Automation:
Industrial automation deals with the optimization of energy-efficient drive systems
by precise measurement and control technologies. Nowadays energy efficiency in
industrial processes are becoming more and more relevant. Semiconductor companies
like Infineon Technologies are offering 8-bit microcontroller applications for example
found in motor controls, general purpose pumps, fans, and e-bikes to reduce energy
consumption and thus increase efficiency.
1.6 Limitations to Automation:
Current technology is unable to automate all the desired tasks. As a process
becomes increasingly automated, there is less and less labour to be saved or quality
improvement to be gained. This is an example of both diminishing returns and the logistic
function.
Similar to the above, as more and more processes become automated, there are fewer
remaining non-automated processes. This is an example of exhaustion of opportunities.

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CHAPTER 2
PROGRAMMABLE LOGIC CONTROLLER
2.1 History of PLC’S:
In the 1960's Programmable Logic Controllers were first developed to replace
relays and relay control systems. Relays, while very useful in some applications, also have
some problems. The primary reason for designing such a device was eliminating the large
cost involved in replacing the complicated relay based machine control systems for major
U.S. car manufacturers. These controllers eliminated the need of rewiring and adding
additional hardware for every new configuration of logic. These, along with other
considerations, led to the development of PLCs. PLC was more improved in 1970’s. In
1973 the ability to communicate between PLCs was added. This also made it possible to
have the controlling circuit quite a ways away from the machine it was controlling.
However, at this time the lack of standardization in PLCs created other problems. This was
improved in the 1980's.The size of PLCs was also reduced then, thus using space even
more efficiently. The 90's increased the collection of ways in which a PLC could be
programmed (block diagrams, instruction list, C, etc.).
2.2 Introduction of PLC’S:
 A programmable logic controller (PLC) is an industrial computer control system that
continuously monitors the state of input devices and makes decisions based upon a
custom program to control the state of output devices.
 It is designed for multiple inputs and output arrangements, extended temperature
ranges, immunity to electrical noise, and resistance to vibration and impact.
 They are used in many industries such as oil refineries, manufacturing lines, conveyor
systems and so on, wherever there is a need to control devices the PLC provides a
flexible way to "soft wire" the components together.
 The basic units have a CPU (a computer processor) that is dedicated to run one
program that monitors a series of different inputs and logically manipulates the outputs
for the desired control. They are meant to be very flexible in how they can be
programmed while also providing the advantages of high reliability (no program
crashes or mechanical failures), compact and economical over traditional control
systems.
In simple words, Programmable Logic Controllers are relay control systems put in a
very small package. This means that one PLC acts basically like a bunch of relays,

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counters, timers, places for data storage, and a few various other things, all in one small
package.
2.3 Architecture And Terminology of PLC’S :
The PLC give output in order to switch things on or off. The PLC’s output is
proportionally activated according on the status of the system’s feedback sensors and input
terminal which is connected to PLC’s. The decision to activate output are based on logic
programmes. The logic programme stored in RAM or ROM memory. The PLC’s also have
same as computer, a CPU, data bus and address bus.
Fig 2.1: PLC’s internal architecture
The next diagram shows a simplified diagram of PLC’s structure. The central
processing unit control everything according to a programme stored in a memory
(RAM/ROM ).
Fig 2.2: Simplified PLC’s structure
INPUT TERMINAL
OUTPUT TERMINAL
RUN
COMMON
RAM
/RO
M
CPU
SOCKETS

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Everything is interconnected by two buses ,the address bus and data bus . The system must
be able to communicate with external devices such as programmers, display moniter and
A/D converter.
Fig 2.3: Basic PLC sections
2.4 PLCs contain four basic sections:
1. Central processing unit (CPU)
2. Memory: RAM, and ROM
3. Input/output module
4. Power supply
2.4.1 Central Processing Unit (C.P.U):
Like other computerized devices, there is a Central Processing Unit (CPU) in a PLC.
The CPU, which is the “brain” of a PLC, does the following operations:
 Updating inputs and outputs. This function allows a PLC to read the status of its
inputterminals and energize or de-energize its output terminals.

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 Performing logic and arithmetic operations. A CPU conducts all the mathematic
andlogic operations involved in a PLC.
 Communicating with memory. The PLC’s programs and data are stored in
memory.When a PLC is operating, its CPU may read or change the contents of memory
locations.
 Scanning application programs. An application program, which is called a ladder logic
program, is a set of instructions written by a PLC programmer. The scanning
functionallows the PLC to execute the application program as specified by the
programmer.
 Communicating with a programming terminal. The CPU transfers program and
databetween itself and the programming terminal.
A PLC’s CPU is controlled by operating system software. The operating system software
is a group of supervisory programs that are loaded and stored permanently in the PLC’s
memory by the PLC manufacturer.
2.4.2 Input/ Output module:
2.4.2.1 Input module:
In smaller PLCs the inputs are normally built in and are specified when purchasing
the PLC. For larger PLCs the inputs are purchased as modules, or cards, with 8 or 16
inputs of the same type on each card.The list below shows typical ranges for input
voltages.
12-24 Vdc
100-120 Vac
10-60 Vdc
12-24 Vac/dc
5 Vdc (TTL)
200-240 Vac
48 Vdc
24 Vac
PLC input cards rarely supply power, this means that an external power supply is needed
to supply power for the inputs and sensors. The example in See An AC Input Card shows
how to connect an AC input card.

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Fig 2.4: Input card connect with external power supply
In the example there are two inputs, one is a normally open push button, and the second is
a temperature switch, or thermal relay. Both of the switches are powered by the hot output
of the 24Vac power supply - this is like the positive terminal on a DC supply. Power is
supplied to the left side of both of the switches. When the switches are open there is no
voltage passed to the input card. If either of the switches are closed power will be supplied
to the input.
Fig 2.5: Input side internal circuit
PLC input must convert a variety of logic level to the 5Vdc logic levels used on the data
bus. This can be done with the circuit which is shown in fig (2.5).This circuit is opto
coupler circuit. This circuit electrically isolate the external electrical circuitry from internal
circuitry. Other circuit component guard to reverse voltage polarity.

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2.4.2.2 Output Module:
As with input modules, output modules rarely supply any power, but instead act as
switches. External power supplies are connected to the output card and the card will switch
the power on or off for each output. Typical output voltages are listed below
120 Vac
24 Vdc
12-48 Vac
12-48 Vdc
5Vdc (TTL)
230 Vac
These cards typically have 8 to 16 outputs of the same type and can be purchased
with different current ratings. A common choice when purchasing output cards is relays,
transistors or triacs. Relays are the most flexible output devices. They are capable of
switching both AC and DC outputs. But, they are slower (about 10ms switching is typical),
they are bulkier and costly.
Fig 2.6: output card connected with various loads
In this example the outputs are connected to a low current light bulb (lamp) and a relay
coil. Consider the circuit through the lamp, starting at the 24Vdc supply. When the output
07 is on, current can flow in 07 to the COM, thus completing the circuit, and allowing the
light to turn on. If the output is off the current cannot flow, and the light will not turn on.
The output 03 for the relay is connected in a similar way. When the output 03 is on,
current will flow through the relay coil to close the contacts and supply 120Vac to the
motor.

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Fig 2.7: Output side internal circuit
PLC output must convert the 5Vdc logic levels on the PLC data bus to external
voltage levels. This can be done with the circuit which is shown in fig(2.7).In this circuit
the relay coil is energized by 5Vdc and close the relay contact and the output circuit is
complete.
2.4.3 Memory:
The memory unit of a PLC is the registry where the programs are stored. The
fundamental unit of memory is the word. Words are made up of bits. A bit is a single piece
of data. It contains information on only two states (ON/OFF or YES/NO). Longer words
contain more information within. Programs are combination of words that produce control
logic.
To operate the PLC system there is a need for it to access the data to be processed
and instructions, that is, the program, which informs it how the data is to be processed.
Both are stored in the PLC memory for access during processing.
PLC memory has following types:
2.4.3.1 ROM(Read Only Memory ):
ROM stores programs and data and cannot be changed after the memory chip has
been manufactured. ROM memory is non-volatile, meaning that its contents will not be
lost if power is lost. ROM is used by the PLC for the operating system.
2.4.3.2 RAM(Random Access Memory):
RAM is designed so that information can be written into or read from the memory.
RAM is used as a temporary storage area of data that may need to be quickly changed.
RAM is volatile, meaning that the data stored in RAM will be lost if power is lost. A
battery backup is required to avoid losing data in the event of a power loss.

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2.4.3.3 EPROM (Erasable Programmable Read Only Memory):
This is memory that can be programmed to behave like ROM, but it can be erased
with ultraviolet light and reprogrammed.
2.4.3.4 EEPROM (Electronically Erasable Programmable Read Only Memory):
This memory can store programs like ROM. It can be programmed and erased
using a voltage, so it is becoming more popular than EPROMs.
2.4.4 Power Supply:
PLCs and their constituting modules are equipped with power generated from a
power supply. The power supply converts power line voltages into those required by the
solid-state components. It may be integral or separately mounted . It drives the Central
Processor Unit, I/O logic signals, memory unit and some peripheral devices. The
expansion of I/O has led to increased power requirement of some PLCs.
2.5 Scan Cycle And Scan Time:
2.5.1 Scan Cycle :
PLC operates by continually scanning the program and acting upon the instructions
, one at a time, to switch on or off the various outputs. In order to do this PLC first scans
all the inputs and stores their states in memory. Then it carries out program scan and
decides which outputs should be high according to the program logic. Then finally it
updates these values to the output table, making the required outputs go high. At this point
PLC checks its own operating system and if everything is ok, it goes back to scanning
inputs all over again.
Fig 2.8: PLC scan cycle
Whenever a programme is executed in a PLC, before changing any output state, the
processor scan the input table and the entire programe, which gives rise to state of the
output device according to the program logic. These value are then updated to the output

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table making the devices connected to the output module on or off. Hence PLC scan cycle
consist of three step shown in a block diagram.
2.5.2 Scan time:
Time taken by PLC to execute these three step (checking input status, executing
program, updating output status)is denoted by scan time.
2.6 PROGRAMMING LANGAUGE USED TO PROGRAM PLC:
While Ladder Logic is the most commonly used PLC programming language, but it is
not the only one. Following table lists some of the Languages that are used to program a
PLC.
 Structured Text(ST)
 Functional block Diagram (FBD)
 Ladder Diagram(LD).
2.6.1 Structured Text (ST):
The Structured Text consists of a series of instructions which, as determined in
high level languages, ("IF..THEN..ELSE") or in loops (WHILE..DO) can be executed.
Example:
IF value < 7 THEN
WHILE value < 8 DO
value:=value+1;
END_WHILE;
END_IF;
2.6.2 Function Block Diagram (FBD):
The Function Block Diagram is a graphically oriented programming language. It
works with a list of networks whereby each network contains a structure which represents
either a logical or arithmetic expression, the call of a function block, a jump, or a return
instruction.
Fig 2.9: Function Block Diagram

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2.6.3 Ladder Diagram (LD):
The Ladder Diagram is also a graphics oriented programming language which
approaches the structure of an electric circuit. Ladder Diagram consists of a series of
networks. Each network consists on the left side of a series of contacts which pass on from
left to right the condition "ON" or "OFF" which correspond to the Boolean values TRUE
and FALSE. To each contact belongs a Boolean variable. If this variable is TRUE, then
condition pass from left to right.
Fig 2.10: ladder diagram
2.7 Applications of PLC:
In the present industrial world, a flexible system that can be controlled by user at
site is preferred. Systems, whose logic can be modified but still, used without disturbing
its connection to external world, is achieved by PLC. Utilizing the industrial sensors such
as limit switches, ON-OFF switches, timer contact, counter contact etc., PLC controls the
total system. The drive to the solenoid valves, motors, indicators, enunciators, etc are
controlled by the PLCs.
The above said controlling elements (normally called as inputs of PLCs) and
controlled elements (called as outputs of PLCs) exist abundantly in any industry. These
inputs, outputs, timers, counters, auxiliary contacts are integral parts of all industries. As
such, it is difficult to define where a PLC cannot be used.
Proper application of a PLC begins with conversion of information into convenient
parameters to save money, time and effort and hence easy operation in plants and
laboratories.
The areas where PLC is used maximum are as follows:
1. The batch processes in chemical, cement, food and paper industries which are
sequential in nature, requiring time of event based decisions is controlled by PLCs.
2. In large process plants PLCs are being increasingly used for automatic start up and
shut down of critical equipment. A PLC ensures that equipment cannot be started
unless all the permissive conditions for safe start have seen established. It also

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monitors the conditions necessary for safe running of the equipment and trips the
equipment whenever any abnormality in the system is detected.
3. The PLC can be programmed to function as an energy management system for boiler
control for maximum efficiency and safety.
4. In automation of blender recliners
5. In automation of bulk material handling system at ports.
6. In automation for a ship unloaded.
7. Automation for wagon loaders.
8. For blast furnace charging controls in steel plants.
9. In automation of brick molding press in refractory.
10. In automation for galvanizing unit.
11. For chemical plants process control automation.
12. In automation of a rock phosphate drying and grinding system.
13. Modernization of boiler and turbo generator set.
14. Process visualization for mining application.
15. Criteria display system for power station.
16. As stored programmed automation unit for the operation of diesel generator sets.
17. In Dairy automation and food processing.
18. For a highly modernized pulp paper factory.
19. In automation system for the printing industry.
20. In automation of container transfer crane.
21. In automation of High-speed elevators.
22. In plastic molding process.
23. In automation of machine tools and transfer lines.
24. In Mixing operations and automation of packaging plants.
25. In compressed air plants and gas handling plants.
26. In fuel oil processing plants and water classification plants.
27. To control the conveyor/classifying system.
Thus PLC is ideal for application where plant machine interlock requirements
are finalized at a later stage and need changes during engineering trial runs,
commissioning or normal use.

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CHAPTER 3
SCADA
(SUPERVISORY CONTROL AND DATA ACQUISITION)
3.1 Introduction
SCADA stands for Supervisory Control And Data Acquisition. As the name
indicates, it is not a full control system, but rather focuses on the supervisory level. As
such, it is a purely software package that is positioned on top of hardware to which it is
interfaced, in general via Programmable Logic Controllers (PLCs), or other commercial
hardware modules.
SCADA systems are used to monitor and control a plant or equipment in industries
such as telecommunications, water and waste control, energy, oil and gas refining and
transportation. These systems encompass the transfer of data between a SCADA central
host computer and a number of Remote Terminal Units (RTUs) and/or Programmable
Logic Controllers (PLCs), and the central host and the operator terminals. A SCADA
system gathers information (such as where a leak on a pipeline has occurred), transfers the
information back to a central site, then alerts the home station that a leak has occurred,
carrying out necessary analysis and control, such as determining if the leak is critical, and
displaying the information in a logical and organized fashion.
SCADA systems consist of:
1. One or more field data interface devices, usually RTUs, or PLCs, which interface to
field sensing devices and local control switchboxes and valve actuators
2. A communications system used to transfer data between field data interface devices
and control units and the computers in the SCADA central host. The system can be
radio, telephone, cable, satellite, etc., or any combination of these.
3. A central host computer server or servers (sometimes called a SCADA Center, master
station, or Master Terminal Unit (MTU)
4. A collection of standard and/or custom software [sometimes called Human Machine
Interface (HMI) software or Man Machine Interface (MMI) software] systems used to
provide the SCADA central host and operator terminal application, support the
communications system, and monitor and control remotely located field data interface
devices.

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Fig 3.1: Typical SCADA System
3.2 Types of SCADA:
1. D+R+N (Development +Run + Networking)
2. R+N (Run +Networking)
3. Factory focus (Networking)
3.3 Basic Features of SCADA:
1. Dynamic process Graphic
2. Alarm summery
3. Alarm history
4. Real time trend
5. Historical time trend
6. Security (Application Security)
7. Data base connectivity
8. Device connectivity
9. Scripts
10. Web Browser Client to View and Control
11. Web Browser based engineering
3.4 Generations of SCADA Systems:
SCADA systems have evolved in parallel with the growth and sophistication of
modern Computing technology. The following sections will provide a description of the
following three generations of SCADA systems:

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• First Generation – Monolithic
• Second Generation – Distributed
• Third Generation – Networked
3.4.1 Monolithic SCADA Systems:
When SCADA systems were first developed, the concept of computing in general
centered on “mainframe” systems. Networks were generally non-existent, and each
centralized system stood alone. As a result, SCADA systems were standalone systems with
virtually no connectivity to other systems. The Wide Area Networks (WANs) that were
implemented to communicate with remote terminal units (RTUs) were designed with a
single purpose in mind–that of communicating with RTUs in the field and nothing else. In
addition, WAN protocols in use today were largely unknown at the time. The
communication protocols in use on SCADA networks were developed by vendors of RTU
equipment and were often proprietary. In addition, these protocols were generally very
“lean”, supporting virtually no functionality beyond that required scanning and controlling
points within the remote device. Also, it was generally not feasible to intermingle other
types of data traffic with RTU communications on the network.
Connectivity to the SCADA master station itself was very limited by the system
vendor. Connections to the master typically were done at the bus level via a proprietary
adapter or controller plugged into the Central Processing Unit (CPU) backplane.
Redundancy in these first generation systems was accomplished by the use of two
identically equipped mainframe systems, a primary and a backup, connected at the bus
level.
Fig 3.2: First Generation SCADA Architecture

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The stand by system’s primary function was to monitor the primary and take over
in the event of a detected failure. This type of standby operation meant that little or no
processing was done on the standby system. Figure 3.1 shows a typical first generation
SCADA architecture.
3.4.2 Distributed SCADA Systems:
The next generation of SCADA systems took advantage of developments and
improvement in system miniaturization and Local Area Networking (LAN) technology to
distribute the processing across multiple systems. Multiple stations, each with a specific
function, were connected to a LAN and shared information with each other in real-time.
These stations were typically of the mini-computer class, smaller and less expensive than
their first generation processors. Some of these distributed stations served as
communications processors, primarily communicating with field devices such as RTUs.
Some served as operator interfaces, providing the human-machine interface (HMI) for
system operators. Still others served as calculation processors or database servers. The
distribution of individual SCADA system functions across multiple systems provided more
processing power for the system as a whole than would have been available in a single
processor.
The networks that connected these individual systems were generally based on
LAN protocols and were not capable of reaching beyond the limits of the local
environment. Some of the LAN protocols that were used were of a proprietary nature,
where the vendor created its own network protocol or version thereof rather than pulling
an existing one off the shelf. This allowed a vendor to optimize its LAN protocol for real-
time traffic, but it limited (or effectively eliminated) the connection of network from other
vendors to the SCADA LAN. Figure 11.2 depicts typical second generation SCADA
architecture. Distribution of system functionality across network-connected systems served
not only to increase processing power, but also to improve the redundancy and reliability
of the system as a whole. Rather than the simple primary/standby failover scheme that was
utilized in many first generation systems, the distributed architecture often kept all stations
on the LAN in an online state all of the time.
For example, if an HMI station were to fail, another HMI station could be used to
operate the system, without waiting for failover from the primary system to the secondary.
The WAN used to communicate with devices in the field were largely unchanged by the
development of LAN connectivity between local stations at the SCADA master. These

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external communications networks were still limited to RTU protocols and were not
available for other types of network traffic. As was the case with the first generation of
systems, the second generation of SCADA systems was also limited to hardware, software,
and peripheral devices that were provided or at least selected by the vendor.
Fig 3.3: Second Generation SCADA Architecture
3.4.3 Networked SCADA Systems:
The current generation of SCADA master station architecture is closely related to
that of the second generation, with the primary difference being that of open system
architecture rather than a vendor controlled, proprietary environment. There are still
multiple networked systems, sharing master station functions. There are still RTUs
utilizing protocols that are vendor-proprietary. The major improvement in the third
generation is that of opening the system architecture, utilizing open standards and
protocols and making it possible to distribute SCADA functionality across a WAN and not
just a LAN. Open standards eliminate a number of the limitations of previous generations
of SCADA systems. The utilization of off-the-shelf systems makes it easier for the user to
connect third party peripheral devices (such as monitors, printers, disk drives, tape drives,
etc.) to the system and/or the network. As they have moved to “open” or “off-the-shelf”

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systems, SCADA vendors have gradually gotten out of the hardware development
business. These vendors have looked to system vendors such as Compaq, Hewlett-
Packard, and Sun Microsystems for their expertise in developing the basic computer
platforms and operating system software. This allows SCADA vendors to concentrate their
development in an area where they can add specific value to the system–that of SCADA
master station software.
The major improvement in third generation SCADA systems comes from the use
of WAN protocols such as the Internet Protocol (IP) for communication between the
master station and communications equipment. This allows the portion of the master
station that is responsible for communications with the field devices to be separated from
the master station “proper” across a WAN. Vendors are now producing RTUs that can
communicate with the master station using an Ethernet connection. Figure 5.4represents a
networked SCADA system. Another advantage brought about by the distribution of
SCADA functionality over a WAN is that of disaster survivability. The distribution of
SCADA processing across a LAN in second-generation systems improves reliability, but
in the event of a total loss of the facility housing the SCADA master, the entire system
could be lost as well. By distributing the processing across physically separate locations, it
becomes possible to build a SCADA system that can survive a total loss of any one
location. For some organizations that see SCADA as a super-critical function, this is a real
benefit.
Fig 3.4: Third Generation SCADA Architecture

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3.5 Architecture:
Generally SCADA system is a centralized system which monitors and controls
entire area. It is purely software package that is positioned on top of hardware. A
supervisory system gathers data on the process and sends the commands control to the
process. For example, in the thermal power plant the water flow can be set to specific
value or it can be changed according to the requirement. The SCADA system allows
operators to change the set point for the flow, and enable alarm conditions incase of loss of
flow and high temperature and the condition is displayed and recorded. The SCADA
system monitors the overall performance of the loop. The SCADA system is a centralized
system to communicate with both wire and wireless technology to Clint devices. The
SCADA system controls can run completely all kinds of industrial process.
EX: If too much pressure in building up in a gas pipe line the SCADA system can
automatically open a release valve.
3.5.1 Hardware Architecture:
The generally SCADA system can be classified into two parts:
 Clint layer
 Data server layer
The Clint layer which caters for the man machine interaction. The data server layer
which handles most of the process data activities. The SCADA station refers to the servers
and it is composed of a single PC.
Fig 3.5:Hardware Architecture

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The data servers communicate with devices in the field through process controllers like
PLCs or RTUs. The PLCs are connected to the data servers either directly or via networks
or buses. The SCADA system utilizes a WAN and LAN networks, the WAN and LAN
consists of internet protocols used for communication between the master station and
devices. The physical equipments like sensors connected to the PLCs or RTUs. The RTUs
convert the sensor signals to digital data and sends digital data to master unit.
3.5.2 Software Architecture:
Most of the servers are used for multitasking and real time database. The servers
are responsible for data gathering and handling. The SCADA system consists of a software
program to provide trending, diagnostic data, and manage information such as scheduled
maintenance procedure, logistic information, detailed schematics for a particular sensor or
machine and expert system troubleshooting guides. This means the operator can sea a
schematic representation of the plant being controlled.
EX: alarm checking, calculations, logging and archiving; polling controllers on a set of
parameter, those are typically connected to the server.
3.6 Working Procedure Of SCADA System:
The SCADA system performs the followingfunctions:
 Data Acquisitions
 Data Communication
 Information/Data presentation
 Monitoring/Control
These functions are performed by sensors, RTUs, controller, communication network. The
sensors are used to collect the important information and RTUs are used to send this
information to controller and display the status of the system. According to the status of
the system, the user can give command to other system components. This operation is
done by the communication network.
5.6.1 Data Acquisitions:
Real time system consists of thousand of components and sensors. It is very
important to know the status of particular components and sensors. For example, some

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sensors measure the water flow from the reservoir to water tank and some sensors
measure the value pressure as the water is release from the reservoir.
3.6.2 Data Communication:
The SCADA system uses wired network to communicate between user and
devices. The real time applications use lot of sensors and components which should be
control remotely. The SCADA system uses internet communications. All information is
transmitted through internet using specific protocols. Sensor and relays are not able to
communicate with the network protocols so RTUs used to communicate sensors and
network interface.
3.6.3 Information/Data presentation:
The normal circuit networks have some indicators which can be visible to control
but in the real time SCADA system, there are thousand of sensors and alarm which are
impossible to be handled simultaneously. The SCADA system uses human machine
interface (HMI) to provide all of the information gathered from the various sensors.
3.6.3.1 Human machine interface:
The SCADA system uses human machine interface. The information is displayed
and monitored to be processed by the human. HMI provides the access of multiple control
units which can be PLCs and RTUs. The HMI provides the graphical presentation of the
system. For example, it provides the graphical picture of the pump connected to the tank.
The user can see the flow of the water and pressure of the water. The important part of the
HMI is an alarm system which is activated according to the predefined values.
Fig 3.6 :Human machine interface

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For example: The tank water level alarm is set 60% and 70% values. If the water level
reaches above 60% the alarm gives normal warning and if the water level reach above 70%
the alarm gives critical warning.
3.6.4 Monitoring/Control:
The SCADA system uses different switches to operate each device and displays the
status at the control area. Any part of the process can be turned ON/OFF from the control
station using these switches. SCADA system is implemented to work automatically
without human intervention but at critical situations it is handled by man power.
3.7 SCADA For Remote Industrial Plant:
In large industrial establishments many process occur simultaneously and each
needs to bemonitored, which is actually a complex task. The SCADA systems are used to
monitor and control the equipments in the industrial processes which include water
distribution, oil distribution and power distribution. The main aim of this project is to
process the real time data and control the large scale remote industrial environment. For an
example the temperature sensors are connected to the PLC , which is connected to the PC
at the front end and software is loaded on the computer. The data is collected from the
temperature sensors. The temperature sensors continuously send the signal to the PLC
which accordingly displays these values on its front panel. One can set the parameters like
low limit and high limit on the computer screen. When the temperature of a sensor goes
above set point ,the PLC send a command to the corresponding relay. The heaters
connected through relay contacts are turned OFF and ON.
3.3 Applications Of SCADA:
SCADA systems can be relatively simple, such as one that monitors environmental
conditions of a small office building, or incredibly complex, such as a system that
monitors all the activity in a nuclear power plant or the activity of a municipal water
system. SCADA monitors and controls industrial, infrastructure, or facility-based
processes, as described below:
 Industrial processes include those of manufacturing, production, power generation,
fabrication, and refining, and may run in continuous, batch, repetitive, or discrete modes.
 Infrastructure processes may be public or private, and include water treatment and
distribution, wastewater collection and treatment, oil and gas pipelines, electrical power
transmission and distribution, wind farms, civil defense siren systems, and large
communication systems.

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 Facility processes occur both in public facilities and private ones, including buildings,
airports, ships, and space stations. They monitor and control HVAC, access, and energy
consumption.
Industries that are catered to are:
 Automotive
 Building Automation
 Cement & Glass
 Chemical
 Electronics
 Food and Beverage
 Machinery & Manufacturing
 Aerospace & Defense
 Metals & Mining
 Oil & Gas
 Pharmaceutical
 Power, Utilities & Generation
 Transportation
 Water & Wastewater
6.4 Advantages:
 The SCADA system provides onboard mechanical and graphical information
 The SCADA system is easily expandable. We can add set of control units and sensors
according to the requirement.
 The SCADA system ability to operate critical situations

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CHAPTER 4
CONCLUSION
Automation plays an increasingly important role in the global economy and In
daily experience. With the speed of changing technology today it is easy to lose sight or
knowledge of the basic theory or operation of programmable logic. Automation provides
100% accuracy all time. So the overall savings increases. It provides safety to human
being .Most people simply use the hardware to produce the results they desire. It makes the
operation faster than manual which causes higher production and proper utilization of
utilities. It increases the production by which the cost of each product decreases and
industry profit increases. Hopefully, this report has given the reader a deeper insight into
the inner workings of programmable logic and its role in mechanical operations. The idea
of programmable logic is very simple to understand, but it is the complex programs that
run in the ladder diagrams that make them difficult for the common user to fully
understand. Hopefully this has alleviated some of that confusion. SCADA is used for the
constructive working, using a SCADA system for control ensures a common framework
not only for the development of the specific applications but also for operating the
detectors. Operators experience the same ”look and feel” whatever part of the experiment
they control. However, this aspect also depends to a significant extent on proper
engineering.

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REFERENCES
[1] A.Daneels,W.Salter, "Technology Survey Summary of Study Report", IT-CO/98-08- 09,
CERN,Geneva 26th Aug 1998.
[2] A.Daneels, W.Salter, "Selection and Evaluation of Commercial SCADA Systems for the
Controls of the CERN LHC Experiments", Proceedings of the 1999 International Conference on
Accelerator and Large Experimental Physics Control Systems, Trieste, 1999, p.353.
[3] G.Baribaud et al., "Recommendations for the Use of Fieldbuses at CERN in the LHC Era",
Proceedings of the 1997 International Conference on Accelerator and Large Experimental Physics
Control Systems, Beijing, 1997, p.285.
[4]D. Kandray, Programmable Automation Technologies , Industrial Press, 2010.
[5] W. Bolton, Programmable Logic Controllers, Fifth Edition, Newnes, 2009.
[6]http://www.surecontrols.com/what-is-industrial-automation/