Post on 23-Oct-2014
ACKNOWLEDGEMENT
I would like to express my gratitude to all those who gave me the possibility to complete
this report. I like to thank my HOD giving me permission to commence this report in the first
instance, to do the necessary experimental work and to use departmental data. I am thanking to
all my teachers who gave me the required knowledge, skill and a mental approach within the
training schedule and encouraged the developing interest in this field. I am bound to my Head of
Department of Electrical & Electronics Engineering also my training incharge Er. R.K. Sharma
(HOD) for constant and stimulating support.
I am thankful to my training coordinator Er. Krishan Arora who supported me in my report work.
I want to thank them for all their help, support, interest and valuable hints as well as for the close
look at the final version of the report for English style and grammar, correcting both and offering
suggestions for improvement.
ABSTRACT
Automation has been of high priority for the manufacturing sector, from Ford's first set of
Model-T Assembly lines in the early 1920s to the modern factory floor. With appropriate
automation, the aim was to rationalize the production and keep the process under control.
Instrumentation for measuring process variables assumed a significant role in meeting such
goals. The development of new sensors and instruments took place in stages concurrent with
advancements in science and technology. This paper comprehensively reviews the evolution of
industrial automation. Essentially, it reviews the milestones in the industrial automation and
control systems, the emergence of Distributed Control Systems (DCSs), the advanced control
architecture, the non-conventional technologies for the future and finally the benefits from the
networked system.
An industrial SCADA system will be used for the development of the controls of LHC
experiments. Here we describe the SCADA systems in terms of their architecture, their interface
to the process hardware, the functionality and the application development facilities they
provide. Some attention is also aid to industrial standards to which they abide their planned
evolution as well as the benefits of their use.
AUTOMATION – HISTORY
Ideas for ways of automating tasks have been in existence since the time of the ancient Greeks.
The Greek inventor Hero (fl. about A.D. 50), for example, is credited with having developed an
automated system that would open a temple door when a priest lit a fire on the temple altar. The
real impetus for the development of automation came, however, during the Industrial Revolution
of the early eighteenth century. Many of the steam-powered devices built by James Watt,
Richard Trevithick, Richard Arkwright, Thomas Savory, Thomas Newcomen, and their
contemporaries were simple examples of machines capable of taking over the work of humans.
One of the most elaborate examples of automated machinery developed during this period was
the draw loom designed by the French inventor Basile Bouchon in 1725. The instructions for the
operation of the Bouchon loom were recorded on sheets of paper in the form of holes. The
needles that carried thread through the loom to make cloth were guided by the presence or
absence of those holes. The manual process of weaving a pattern into a piece of cloth through the
work of an individual was transformed by the Bouchon process into an operation that could be
performed mindlessly by merely stepping on a pedal.
CHAPTER – 1 AUTOMATION
INTRODUCTION
Automation is the use of control systems (such as numerical control, programmable logic
control, and other industrial control systems), in concert with other applications of information
technology (such as computer-aided technologies [CAD, CAM]), to control industrial machinery
and processes, 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 with the muscular requirements of work, automation greatly
reduces the need for human sensory and mental requirements as well. Processes and systems can
also be automated.
Types of Automation
Automated machines can be subdivided into two large categories—open-loop and closed-loop
machines, which can then be subdivided into even smaller categories. Open-loop machines are
devices that, once started, go through a cycle and then stop. A common example is the automatic
dishwashing machine. Once dishes are loaded into the machine and a button pushed, the machine
goes through a predetermined cycle of operations: pre-rinse, wash, rinse, and dry, for example. A
human operator may have choices as to which sequence the machine should follow—heavy
wash, light wash, warm and cold, and so on—but each of these operations is alike in that the
machine simply does the task and then stops. Many of the most familiar appliances in homes
today operate on this basis. A microwave oven, a coffee maker, and a CD player are examples.
Larger, more complex industrial operations also use open-cycle operations. For example, in the
production of a car, a single machine may be programmed to place a side panel in place on the
car and then weld it in a dozen or more locations. Each of the steps involved in this process—
from placing the door properly to each of the different welds—takes place according to
instructions programmed into the machine.
Other category in which automation is divided is:
Scientific Automation ( used by scientists)
Industrial Automation ( building management system)
Office Automation ( used by non technical staff)
Role of Computers in Automation
Since the 1960s, the nature of automation has undergone dramatic changes as a result of the
availability of computers. For many years, automated machines were limited by the amount of
feedback data they could collect and interpret. Thus, their operation was limited to a relatively
small number of alternatives. When an automated machine is placed under the control of a
computer, however, that disadvantage disappears. The computer can analyze a vast number of
sensory inputs from a system and decide which of many responses it should make.
Layout of Industrial Automation
AUTOMATION - APPLICATION
Manufacturing companies in virtually every industry are achieving rapid increases in
productivity by taking advantage of automation technologies. When one thinks of automation in
manufacturing, robots usually come to mind. The automotive industry was the early adopter of
robotics, using these automated machines for material handling, processing operations, and
assembly and inspection. Donald A. Vincent, executive vice president, Robotic Industries
Association, predicts a greater use of robots for assembly, paint systems, final trim, and parts
transfer will be seen in the near future.
One can break down automation in production into basically three categories: fixed automation,
programmable automation, and flexible automation. The automotive industry primarily uses
fixed automation, Also known as "hard automation," this refers to an automated production
facility in which the sequence of processing operations is fixed by the equipment layout. A good
example of this would be an automated production line where a series of workstations are
connected by a transfer system to move parts between the stations. What starts as a piece of sheet
metal in the beginning of the process, becomes a car at the end.
Programmable automation is a form of automation for producing products in batches. The
products are made in batch quantities ranging from several dozen to several thousand units at a
time. For each new batch, the production equipment must be reprogrammed and changed over to
accommodate the new product style.
Flexible automation is an extension of programmable automation. Here, the variety of products
is sufficiently limited so that the changeover of the equipment can be done very quickly and
automatically. The reprogramming of the equipment in flexible automation is done off-line; that
is, the programming is accomplished at a computer terminal without using the production
equipment itself.
AUTOMATION- ADVANTAGES
1. Replacing human operator in tedious task.
2. Replacing humans in tasks that should be done in dangerous environment.
3. Making tasks that are beyond human capabilities such as handle too heavy
loads, too large objects, too hot or cold substances or the requirement to make things too
fast or too slow.
4. Economy improvement- sometimes some kinds of automation imply improves in
economy of enterprises, society or most of the humankind.
DISADVANTAGES
1. Technology limits- nowadays technology is not able to automate all desired task.
2. Initial costs are relative high.
CHAPTER – 2 PROGRAMMABLE LOGIC CONTROLLER
INTRODUCTION
A programmable logic controller (PLC) or programmable controller is a digital computer
used for automation of electromechanical processes, such as control of machinery on factory
assembly lines, amusement rides, or lighting fixtures. PLCs are used in many industries and
machines. Unlike general-purpose computers, the PLC is designed for multiple inputs and output
arrangements, extended temperature ranges, immunity to electrical noise, and resistance to
vibration and impact. Programs to control machine operation are typically stored in battery-
backed or non-volatile memory. A PLC is an example of a real time system since output results
must be produced in response to input conditions within a bounded time, otherwise unintended
operation will result.
History
The PLC was invented in response to the needs of the American automotive manufacturing
industry. Programmable controllers were initially adopted by the automotive industry where
software revision replaced the re-wiring of hard-wired control panels when production models
changed.
Before the PLC, control, sequencing, and safety interlock logic for manufacturing automobiles
was accomplished using hundreds or thousands of relays, cam timers, and drum sequencers and
dedicated closed-loop controllers. The process for updating such facilities for the yearly model
change-over was very time consuming and expensive, as electricians needed to individually
rewire each and every relay.
In 1968 GM Hydramatic (the automatic transmission division of General Motors) issued a
request for proposal for an electronic replacement for hard-wired relay systems. The winning
proposal came from Bedford Associates of Bedford, Massachusetts. The first PLC, designated
the 084 because it was Bedford Associates' eighty-fourth project, was the result. Bedford
Associates started a new company dedicated to developing, manufacturing, selling, and servicing
this new product: Modicon, which stood for MOdular DIgital CONtroller. One of the people
who worked on that project was Dick Morley, who is considered to be the "father" of the PLC.
The Modicon brand was sold in 1977 to Gould Electronics, and later acquired by German
Company AEG and then by French Schneider Electric, the current owner.
Vendors of PLCs
Allenbradley( micrologix, SLC, Contrologix)
Schneider(modicon, zelio)
Siemens(s7-200, s7-300)
OMRON
GE-FANUC
Mitsubishi
Features of PLC
Control panel with PLC (grey elements in the center). The unit consists of separate elements,
from left to right; power supply, controller, relay units for in- and output
The main difference from other computers is that PLCs are armored for severe conditions (such
as dust, moisture, heat, cold) and have the facility for extensive input/output (I/O) arrangements.
These connect the PLC to sensors and actuators. PLCs read limit switches, analog process
variables (such as temperature and pressure), and the positions of complex positioning systems.
Some use machine vision. On the actuator side, PLCs operate electric motors, pneumatic or
hydraulic cylinders, magnetic relays, solenoids, or analog outputs. The input/output
arrangements may be built into a simple PLC, or the PLC may have external I/O modules
attached to a computer network that plugs into the PLC.
With each module having sixteen "points" of either input or output, this PLC has the ability to
monitor and control dozens of devices. Fit into a control cabinet, a PLC takes up little room,
especially considering the equivalent space that would be needed by electromechanical relays to
perform the same functions:
The main difference from other computers is that PLC are armored for severe condition (dust,
moisture, heat, cold, etc) and has the facility for extensive input/output (I/O) arrangements.
These connect the PLC to sensors and actuators. PLCs read limit switches, analog process
variables (such as temperature and pressure), and the positions of complex positioning systems.
Some even use machine vision. On the actuator side, PLCs operate electric motors, pneumatic or
hydraulic cylinders, magnetic relays or solenoids, or analog outputs. The input/output
arrangements may be built into a simple PLC, or the PLC may have external I/O modules
attached to a computer network that plugs into the PLC.
Many of the earliest PLCs expressed all decision making logic in simple ladder logic which
appeared similar to electrical schematic diagrams. The electricians were quite able to trace out
circuit problems with schematic diagrams using ladder logic. This program notation was chosen
to reduce training demands for the existing technicians. Other early PLCs used a form of
instruction list programming, based on a stack-based logic solver.
The functionality of the PLC has evolved over the years to include sequential relay control,
motion control, process control, distributed control systems and networking. The data handling,
storage, processing power and communication capabilities of some modern PLCs are
approximately equivalent to desktop computers
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 technicians. 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 ladder logic to more traditional
programming languages such as BASIC and C. Another method is State Logic, a very high-level
programming language designed to program PLCs based on state transition diagrams.
Functionality
The functionality of the PLC has evolved over the years to include sequential relay control,
motion control, process control, distributed control systems 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.
Programming
PLC programs are typically written in a special application on a personal computer, then
downloaded by a direct-connection cable or over a network to the PLC. The program is stored in
the PLC either in battery-backed-up RAM or some other non-volatile flash memory. Often, a
single PLC can be programmed to replace thousands of relays.
IEC 61131-3 currently defines five programming languages for programmable control systems:
FBD (Function block diagram)
LD (Ladder diagram)
ST (Structured text, similar to the Pascal programming language)
IL (Instruction list, similar to assembly language)
SFC (Sequential function chart)
While the fundamental concepts of PLC programming are common to all manufacturers,
differences in I/O addressing, memory organization and instruction sets mean that PLC programs
are never perfectly interchangeable between different makers. Even within the same product line
of a single manufacturer, different models may not be directly compatible.
Wiring In a PLC
Block diagram of a PLC
Generation of Input Signal
Inside the PLC housing, connected between each input terminal and the Common terminal, is an
opto-isolator device (Light-Emitting Diode) that provides an electrically isolated "high" Logic
signal to the computer's circuitry (a photo-transistor interprets the LED's light) when there is 120
VAC power applied between the respective input terminal and the Common terminal. An
indicating LED on the front panel of the PLC gives visual indication of an "energized" input
:
Diagram Showing Energized input terminal X1
Generation of Output Signal
Output signals are generated by the PLC's computer circuitry activating a switching device
(transistor, TRIAC, or even an electromechanical relay), connecting the "Source" terminal to any
of the "Y-" labeled output terminals. The "Source" terminal, correspondingly, is usually
connected to the L1 side of the 120 VAC power source. As with each input, an indicating LED
on the front panel of the PLC gives visual indication of an "energized" output
In this way, the PLC is able to interface with real-world devices such as switches and solenoids.
The actual logic of the control system is established inside the PLC by means of a computer
program. This program dictates which output gets energized under which input conditions.
Although the program itself appears to be a ladder logic diagram, with switch and relay symbols,
there are no actual switch contacts or relay coils operating inside the PLC to create the logical
relationships between input and output. These are imaginary contacts and coils, if you will. The
program is entered and viewed via a personal computer connected to the PLC's programming
port.
Diagram Showing Energized Output Y1
PLC compared with other control systems
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 economic due to the lower cost of the components, which can be optimally chosen
instead of a "generic" solution, and where the non-recurring engineering charges are spread over
thousands or millions of units.
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.
Programmable controllers are widely used in motion control, positioning control and 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.
Digital and analog signals
Digital or 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, 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 4-20 mA or 0 - 10 V input would be converted into an integer
value of 0 - 32767.
Current inputs are less sensitive to electrical noise (i.e. from welders or electric motor starts) than
voltage inputs.
Example
As an example, say a facility needs to store water in a tank. The water is drawn from the tank by
another system, as needed, and our example system must manage the water level in the tank.
Using only digital signals, the PLC has two digital inputs from float switches (Low Level and
High Level). When the water level is above the switch it closes a contact and passes a signal to
an input. The PLC uses a digital output to open and close the inlet valve into the tank.
When the water level drops enough so that the Low Level float switch is off (down), the PLC
will open the valve to let more water in. Once the water level rises enough so that the High Level
switch is on (up), the PLC will shut the inlet to stop the water from overflowing. This rung is an
example of seal in logic. The output is sealed in until some condition breaks the circuit.
|| Low Level High Level Fill Valve ||------[/]------|------[/]----------------------(OUT)---------|| | || | || | || Fill Valve | ||------[ ]------| || || |
An analog system might use a water pressure sensor or a load cell, and an adjustable (throttling)
dripping out of the tank, the valve adjusts to slowly drip water back into the tank.
In this system, to avoid 'flutter' adjustments that can wear out the valve, many PLCs incorporate
"hysteresis" which essentially creates a “dead band” of activity? A technician adjusts this dead
band so the valve moves only for a significant change in rate. This will in turn minimize the
motion of the valve, and reduce its wear.
A real system might combine approaches, using float switches and simple valves to prevent
spills, and a rate sensor and rate valve to optimize refill rates and prevent water hammer. Backup
and maintenance methods can make a real system very complicated.
CHAPTER – 3 PROGRAMMING WITH PLC
Early PLCs, up to 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. Programs were stored on cassette tape cartridges.
Facilities for printing and documentation were very minimal due to lack of memory capacity.
More recently, PLC programs are typically written in a special application on a personal
computer, then downloaded by a direct-connection cable or over a network to the PLC. The very
oldest PLCs used non-volatile magnetic core memory but now the program is stored in the PLC
either in battery-backed-up RAM or some other non-volatile flash memory.
Early PLCs were designed to be used by electricians who would learn PLC programming on the
job. These PLCs were programmed in "ladder logic", which strongly resembles a schematic
diagram of relay logic. Modern PLCs can be programmed in a variety of ways, from ladder logic
to more traditional programming languages such as BASIC and C. Another method is State
Logic, a Very High Level Programming Language designed to program PLCs based on State
Transition Diagrams.
Ladder logic
Ladder logic is a method of drawing electrical logic schematics. It is now a graphical language
very popular for programming Programmable Logic Controllers (PLCs). It was originally
invented to describe logic made from relays. The name is based on the observation that programs
in this language resemble ladders, with two vertical "rails" and a series of horizontal "rungs"
between them.
A program in ladder logic, also called a ladder diagram, is similar to a schematic for a set of
relay circuits. An argument that aided the initial adoption of ladder logic was that a wide variety
of engineers and technicians would be able to understand and use it without much additional
training, because of the resemblance to familiar hardware systems. (This argument has become
less relevant given that most ladder logic programmers have a software background in more
conventional programming languages, and in practice implementations of ladder logic have
characteristics — such as sequential execution and support for control flow features — that make
the analogy to hardware somewhat imprecise.)
Ladder logic is widely used to program PLCs, where sequential control of a process or
manufacturing operation is required. Ladder logic is useful for simple but critical control
systems, or for reworking old hardwired relay circuits. As programmable logic controllers
became more sophisticated it has also been used in very complex automation systems.
Ladder logic can be thought of as a rule-based language, rather than a procedural language. A
"rung" in the ladder represents a rule. When implemented with relays and other
electromechanical devices, the various rules "execute" simultaneously and immediately. When
implemented in a programmable logic controller, the rules are typically executed sequentially by
software, in a loop. By executing the loop fast enough, typically many times per second, the
effect of simultaneous and immediate execution is obtained. In this way it is similar to other rule-
based languages, like spreadsheets or SQL. However, proper use of programmable controllers
requires understanding the limitations of the execution order of rungs.
Example of a simple ladder logic program
The language itself can be seen as a set of connections between logical checkers (relay contacts)
and actuators (coils). If a path can be traced between the left side of the rung and the output,
through asserted (true or "closed") contacts, the rung is true and the output coil storage bit is
asserted (1) or true. If no path can be traced, then the output is false (0) and the "coil" by analogy
to electromechanical relays is considered "de-energized". The analogy between logical
propositions and relay contact status is due to Claude Shannon.
Ladder logic has "contacts" that "make" or "break" "circuits" to control "coils." Each coil or
contact corresponds to the status of a single bit in the programmable controller's memory. Unlike
electromechanical relays, a ladder program can refer any number of times to the status of a single
bit, equivalent to a relay with an indefinitely large number of contacts.
So-called "contacts" may refer to inputs to the programmable controller from physical devices
such as pushbuttons and limit switches, or may represent the status of internal storage bits which
may be generated elsewhere in the program.
Each rung of ladder language typically has one coil at the far right. Some manufacturers may
allow more than one output coil on a rung.
--( )-- a regular coil, true when its rung is true
--(\)-- a "not" coil, false when its rung is true
--[ ]-- A regular contact, true when its coil is true (normally false)
--[\]-- A "not" contact, false when its coil is true (normally true)
The "coil" (output of a rung) may represent a physical output which operates some device
connected to the programmable controller, or may represent an internal storage bit for use
elsewhere in the program.
Generally Used Instructions & symbol For PLC Programming
Input Instruction
--[ ]-- This Instruction is Called IXC or Examine If Closed.
ie; If a NO switch is actuated then only this instruction will be true. If a NC switch is
actuated then this instruction will not be true and hence output will not be generated.
--[\]-- This Instruction is Called IXO or Examine If Open
ie; If a NC switch is actuated then only this instruction will be true. If a NC switch is
actuated then this instruction will not be true and hence output will not be generated.
Output Instruction
--( )-- This Instruction Shows the States of Output.
ie; If any instruction either XIO or XIC is true then output will be high. Due to high
output a 24 volt signal is generated from PLC processor.
Rung Rung is a simple line on which instruction are placed and logics are created.
E.g. here is an example of what one rung in a ladder logic program might look like. In real life,
there may be hundreds or thousands of rungs.
For example
1. ----[ ]---------|--[ ]--|------( )--
X | Y | S
| |
|--[ ]--|
Z
The above realises the function: S = X AND (Y OR Z)
Typically, complex ladder logic is 'read' left to right and top to bottom. As each of the lines (or
rungs) are evaluated the output coil of a rung may feed into the next stage of the ladder as an
input. In a complex system there will be many "rungs" on a ladder, which are numbered in order
of evaluation.
1. ----[ ]-----------|---[ ]---|----( )--
X | Y | S
| |
|---[ ]---|
Z
2. ---- [ ]----[ ] -------------------( )--
S X T
T = S AND X where S is equivalent to #1. above
This represents a slightly more complex system for rung 2. After the first line has been
evaluated, the output coil (S) is fed into rung 2, which is then evaluated and the output coil T
could be fed into an output device (buzzer, light etc..) or into rung 3 on the ladder. (Note that the
contact X on the 2nd rung serves no useful purpose, as X is already a 'AND' function of S from
the 1st rung.)
This system allows very complex logic designs to be broken down and evaluated.
More practical examples
Example-1
------[ ]--------------[ ]----------------O---
Key Switch 1 Key Switch 2 Door Motor
This circuit shows two key switches that security guards might use to activate an electric motor
on a bank vault door. When the normally open contacts of both switches close, electricity is able
to flow to the motor which opens the door. This is a logical AND.
Example-2
Often we have a little green "start" button to turn on a motor, and we want to turn it off with a
big red "Stop" button.
--+----[ ]--+----[\]----( )---
| start | stop run
| |
+----[ ]--+
run
-------[ ]--------------( )---
run motor
Example With PLC
Consider the following circuit and PLC program:
-------[ ]--------------( )---
run motor
When the pushbutton switch is unactuated (unpressed), no power is sent to the X1 input of the
PLC. Following the program, which shows a normally-open X1 contact in series with a Y1 coil,
no "power" will be sent to the Y1 coil. Thus, the PLC's Y1 output remains de-energized, and the
indicator lamp connected to it remains dark.
If the pushbutton switch is pressed, however, power will be sent to the PLC's X1 input. Any and
all X1 contacts appearing in the program will assume the actuated (non-normal) state, as though
they were relay contacts actuated by the energizing of a relay coil named "X1". In this case,
energizing the X1 input will cause the normally-open X1 contact will "close," sending "power"
to the Y1 coil. When the Y1coilof the program "energizes," the real Y1 output will become
energized, lighting up the lamp connected to it.
When the lamp is actuated
It must be understood that the X1 contact, Y1 coil, connecting wires, and "power" appearing in
the personal computer's display are all virtual. They do not exist as real electrical components.
They exist as commands in a computer program -- a piece of software only -- that just happens to
resemble a real relay schematic diagram.
Equally important to understand is that the personal computer used to display and edit the PLC's
program is not necessary for the PLC's continued operation. Once a program has been loaded to
the PLC from the personal computer, the personal computer may be unplugged from the PLC,
and the PLC will continue to follow the programmed commands. I include the personal computer
display in these illustrations for your sake only, in aiding to understand the relationship between
real-life conditions (switch closure and lamp status) and the program's status ("power" through
virtual contacts and virtual coils).
The true power and versatility of a PLC is revealed when we want to alter the behavior of a
control system. Since the PLC is a programmable device, we can alter its behavior by changing
the commands we give it, without having to reconfigure the electrical components connected to
it. For example, suppose we wanted to make this switch-and-lamp circuit function in an inverted
fashion: push the button to make the lamp turn off, and release it to make it turn on. The
"hardware" solution would require that a normally-closed pushbutton switch be substituted for
the normally-open switch currently in place. The "software" solution is much easier: just alter the
program so that contact X1 is normally-closed rather than normally-open.
CHAPTER – 4 SUPERVISORY CONTROL AND DATA
ACQUISITION SYSTEM
Introduction
SCADA stands for supervisory control and data acquisition. It generally refers to an industrial
control system: a computer system monitoring and controlling a process. The process can be
industrial, infrastructure or facility-based 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, civil defense siren systems, and large communication
systems.
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.
What is Data Acquisition?
Data acquisition is the process of retrieving control information from the equipment which is out
of order or may lead to some problem or when decisions are need to be taken according to the
situation in the equipment. So this acquisition is done by continuous monitoring of the
equipment to which it is employed. The data accessed are then forwarded onto a telemetry
system ready for transfer to the different sites. They can be analog and digital information
gathered by sensors, such as flow meter, ammeter, etc. It can also be data to control equipment
such as actuators, relays, valves, motors, etc.
Vendors of SCADA:
Wonder ware – In Touch
Siemens – WinCc
Rockwell (Allen Bradley) – RS view
GE Fanuc – Cimplicity
Schneider – VG-look, VG-citect
Modicon – Moviecon
Intelluation – I-fix
KPIT – Astra
Here we will work on In Touch 7.0(Wonderware)
Why and where we use SCADA?
SCADA can be used to monitor and control plant or equipment. The control may be automatic,
or initiated by operator commands. The data acquisition is accomplished firstly by the RTU's
(remote Terminal Units) scanning the field inputs connected to the RTU (RTU’s may also be
called a PLC - programmable logic controller). This is usually at a fast rate. The central host will
scan the RTU's (usually at a slower rate.) The data is processed to detect alarm conditions, and if
an alarm is present, it will be displayed on special alarm lists. Data can be of three main types.
Analogue data (i.e. real numbers) will be trended (i.e. placed in graphs). Digital data (on/off)
may have alarms attached to one state or the other. Pulse data (e.g. counting revolutions of a
meter) is normally accumulated or counted.
These systems are used not only in industrial processes. For example, Manufacturing, steel
making, power generation both in conventional, nuclear and its distribution, chemistry, but also
in some experimental facilities such as laboratories research, testing and evaluation centers,
nuclear fusion. The size of such plants can range from as few as 10 to several 10 thousands
input/output (I/O) channels. However, SCADA systems evolve rapidly and are now penetrating
the market of plants with a number of I/O channels of several 100K.
The primary interface to the operator is a graphical display (mimic) usually via a PC
Screen which shows a representation of the plant or equipment in graphical form. Live data is
shown as graphical shapes (foreground) over a static background. As the data changes in the
field, the foreground is updated. E.g. a valve may be shown as open or closed. Analog data can
be shown either as a number, or graphically. The system may have many such displays, and the
operator can select from the relevant ones at any time.
SCADA systems were first used in the 1960s.SCADA systems have made substantial
progress over the recent years in terms of functionality, scalability, performance and openness
such that they are an alternative to in house development even for very demanding and complex
control systems as those of physics experiments. SCADA systems used to run on DOS, VMS
and UNIX; in recent years all SCADA vendors have moved to NT and some also to Linux.
Common system components
A SCADA System usually consists of the following subsystems:
A Human-Machine Interface or HMI is the apparatus which presents process data to a
human operator, and through this, the human operator monitors and controls the process.
A supervisory (computer) system, gathering (acquiring) data on the process and sending
commands (control) to the process.
Remote Terminal Units (RTUs) connecting to sensors in the process, converting sensor
signals to digital data and sending digital data to the supervisory system.
Programmable Logic Controller (PLCs) used as field devices because they are more
economical, versatile, flexible, and configurable than special-purpose RTUs.
Communication infrastructure connecting the supervisory system to the Remote Terminal
Units.
Supervision vs. control
There is, in several industries, considerable confusion over the differences between SCADA
systems and Distributed control systems (DCS). Generally speaking, a SCADA system usually
refers to a system that coordinates, but does not control processes in real time. The discussion on
real-time control is muddied somewhat by newer telecommunications technology, enabling
reliable, low latency, high speed communications over wide areas. Most differences between
SCADA and DCS are culturally determined and can usually be ignored. As communication
infrastructures with higher capacity become available, the difference between SCADA and DCS
will fade.
Architecture
In this section we are going to details which describe the common architecture required
for the SCADA products.
Hardware Architecture
The basic hardware of the SCADA system is distinguished into two basic layers: the
"client layer" which caters for the man machine interaction and the "data server layer" which
handles most of the process data control activities. The data servers communicate with devices in
the field through process controllers. Process controllers, e.g. PLC’s, are connected to the data
servers either directly or via networks or fieldbuses that are proprietary (e.g. Siemens H1), or
non-proprietary (e.g. Profibus). Data servers are connected to each other and to client stations via
an Ethernet LAN. Fig.1. shows typical hardware architecture.
Figure 1: Typical Hardware Architecture
Communication
Internal Communication:
Server-client and server-server communication is in general on a publish-subscribe and
event-driven basis and uses a TCP/IP protocol, i.e., a client application subscribes to a parameter
which is owned by a particular server application and only changes to that parameter are then
communicated to the client application.
Access to Devices:
The data servers poll the controllers at a user defined polling rate. The polling rate may
be different for different parameters. The controllers pass the requested parameters to the data
servers. Time stamping of the process parameters is typically performed in the controllers and
this time-stamp is taken over by the data server. If the controller and communication protocol
used support unsolicited data transfer then the products will support this too.
The products provide communication drivers for most of the common PLCs and widely
used field-buses, e.g., Modbus. Of the three fieldbuses that are recommended are, both Profibus
and Worldfip are supported but CANbus often not. Some of the drivers are based on third party
products (e.g., Applicom cards) and therefore have additional cost associated with them. VME
on the other hand is generally not supported.
A single data server can support multiple communications protocols; it can generally
support as many such protocols as it has slots for interface cards. The effort required to develop
new drivers is typically in the range of 2-6 weeks depending on the complexity and similarity
with existing drivers, and a driver development tool kit is provided for this.
Interfacing
Application Interfaces / Openness
The provision of OPC client functionality for SCADA to access devices in an open and
standard manner is developing. There still seems to be a lack of devices/controllers, which
provide OPC server software, but this improves rapidly as most of the producers of controllers
are actively involved in the development of this standard.
The products also provide
an Open Data Base Connectivity (ODBC) interface to the data in the archive/logs, but not
to the configuration database,
an ASCII import/export facility for configuration data,
a library of APIs supporting C, C++, and Visual Basic (VB) to access data in the RTDB,
logs and archive. The API often does not provide access to the product's internal features
such as alarm handling, reporting, trending, etc.
The PC products provide support for the Microsoft standards such as Dynamic Data
Exchange (DDE) which allows e.g. to visualize data dynamically in an EXCEL spreadsheet,
Dynamic Link Library (DLL) and Object Linking and Embedding (OLE).
Database
The configuration data are stored in a database that is logically centralized but physically
distributed and that is generally of a proprietary format. For performance reasons, the RTDB
resides in the memory of the servers and is also of proprietary format. The archive and logging
format is usually also proprietary for performance reasons, but some products do support logging
to a Relational Data Base Management System (RDBMS) at a slower rate either directly or via
an ODBC interface.
Scalability
Scalability is understood as the possibility to extend the SCADA based control system by
adding more process variables, more specialized servers (e.g. for alarm handling) or more
clients. The products achieve scalability by having multiple data servers connected to multiple
controllers. Each data server has its own configuration database and RTDB and is responsible for
the handling of a sub-set of the process variables (acquisition, alarm handling, archiving).
SCADA as a System
A SCADA System usually consists of the following subsystems:
A Human-Machine Interface or HMI is the apparatus which presents process data to a
human operator, and through this, the human operator monitors and controls the process.
A supervisory (computer) system, gathering (acquiring) data on the process and sending
commands (control) to the process.
Remote Terminal Units (RTUs) connecting to sensors in the process, converting
sensor signals to digital data and sending digital data to the supervisory system.
Programmable Logic Controller (PLCs) used as field devices because they are more
economical, versatile, flexible, and configurable than special-purpose RTUs.
Communication infrastructure connecting the supervisory system to the Remote
Terminal Units.
TYPICAL SCADA SYSTEM
System Concept
The term SCADA usually refers to centralized systems which monitor and control entire sites, or
complexes of systems spread out over large areas (anything between an industrial plant and a
country). Most control actions are performed automatically by remote terminal units ("RTUs") or
by programmable logic controllers ("PLCs"). Host control functions are usually restricted to
basic overriding or supervisory level intervention. For example, a PLC may control the flow of
cooling water through part of an industrial process, but the SCADA system may allow operators
to change the set points for the flow and enable alarm conditions, such as loss of flow and high
temperature, to be displayed and recorded. The feedback control loop passes through the RTU or
PLC, while the SCADA system monitors the overall performance of the loop.
Data acquisition begins at the RTU or PLC level and includes meter readings and equipment
status reports that are communicated to SCADA as required. Data is then compiled and
formatted in such a way that a control room operator using the HMI can make supervisory
decisions to adjust or override normal RTU (PLC) controls.
SCADA systems typically implement a distributed database, commonly referred to as a tag
database, which contains data elements called tags or points. A point represents a single input or
output value monitored or controlled by the system. Points can be either "hard" or "soft". A hard
point represents an actual input or output within the system, while a soft point results from logic
and math operations applied to other points. (Most implementations conceptually remove the
distinction by making every property a "soft" point expression, which may, in the simplest case,
equal a single hard point.) Points are normally stored as value-timestamp pairs: a value and the
timestamp when it was recorded or calculated. A series of value-timestamp pairs gives the
history of that point. It's also common to store additional metadata with tags, such as the path to
a field device or PLC register, design time comments, and alarm information.
Functionality
Access Control
Users are allocated to groups, which have defined read/write access privileges to the
process parameters in the system and often also to specific product functionality.
MMI
The products support multiple screens, which can contain combinations of synoptic
diagrams and text. They also support the concept of a "generic" graphical object with links to
process variables. These objects can be "dragged and dropped" from a library and included into a
synoptic diagram. Most of the SCADA products that were evaluated decompose the process in
"atomic" parameters (e.g. a power supply current, its maximum value, its on/off status, etc.) to
which a Tag-name is associated. The Tag-names used to link graphical objects to devices can be
edited as required. The products include a library of standard graphical symbols, many of which
would however not be applicable to the type of applications encountered in the experimental
physics community. Standard windows editing facilities are provided: zooming, re-sizing,
scrolling... On-line configuration and customization of the MMI is possible for users with the
appropriate privileges. Links can be created between display pages to navigate from one view to
another.
Trending
The products all provide trending facilities and one can summarize the common
capabilities as follows:
the parameters to be trended in a specific chart can be predefined or defined on-line
a chart may contain more than 8 trended parameters or pens and an unlimited number of
charts can be displayed (restricted only by the readability)
real-time and historical trending are possible, although generally not in the same chart
historical trending is possible for any archived parameter
zooming and scrolling functions are provided
parameter values at the cursor position can be displayed
The trending feature is either provided as a separate module or as a graphical object
(ActiveX), which can then be embedded into a synoptic display. XY and other statistical analysis
plots are generally not provided.
Alarm Handling
Alarm handling is based on limit and status checking and performed in the data servers.
More complicated expressions (using arithmetic or logical expressions) can be developed by
creating derived parameters on which status or limit checking is then performed. The alarms are
logically handled centrally, i.e., the information only exists in one place and all users see the
same status (e.g., the acknowledgement), and multiple alarm priority levels (in general many
more than 3 such levels) are supported.
It is generally possible to group alarms and to handle these as an entity (typically filtering
on group or acknowledgement of all alarms in a group). Furthermore, it is possible to suppress
alarms either individually or as a complete group. The filtering of alarms seen on the alarm page
or when viewing the alarm log is also possible at least on priority, time and group. However,
relationships between alarms cannot generally be defined in a straightforward manner. E-mails
can be generated or predefined actions automatically executed in response to alarm conditions.
Automation
The majority of the products allow actions to be automatically triggered by events. A
scripting language provided by the SCADA products allows these actions to be defined. In
general, one can load a particular display, send an Email, run a user defined application or script
and write to the RTDB.
The concept of recipes is supported, whereby a particular system configuration can be
saved to a file and then re-loaded at a later date. Sequencing is also supported whereby, as the
name indicates, it is possible to execute a more complex sequence of actions on one or more
devices. Sequences may also react to external events. Some of the products do support an expert
system but none has the concept of a Finite State Machine (FSM).
Features of SCADA
Dynamic Process Graphic mimics developed in SCADA software should resemble the process
mimic. SCADA should have good library of symbols so that you can develop the mimic as per
requirement. Once the operator sees the screen he should know what is going on in the plant.
Real Time and Historical Trend the trend play very important role in the process operation. If
your batch fails or the plant trips, you can simply go to the historical trend data and do the
analysis. You can have better look of the parameters through the trend. Ex. We commission a
SCADA system for Acid Regeneration plant where the plant has to be operated on 850-deg
temperature. If the operator operates the plant at 900 deg you can imagine how much additional
LPG he is putting into the reactor. Again what will happen to the bricks of the reactor? So the
production manger’s first job will be to go through the trends how the operators are operating the
plant. Even when the plant trips there are more than 25 probable reasons for the sample but if
you go through the history trends, it’s very easy to identify the problem.
Alarms have a very critical role in automation. Generally you have alarm states for each
inputs/outputs like your temperature should not cross 80 deg or lever should be less than 60. So
if the parameters go in alarm state the operator should be intimated with alarm. Most of the
SCADA software support four types of alarms like LOLO,LO,HI and HIHI. Deadband the value
of deadband defines the range after which a high low alarm condition returns to normal.
Alarms are the most important part of the plant control applications because the operator must
know instantly when something goes wrong. It is often equally important to have a record of
alarms and whether an alarm was acknowledged. An alarm occurs when something goes wrong.
It can signal that a device or process has ceased operating within acceptable, predefined limits or
it can indicate breakdown, wear or process malfunction.
Recipe Management is an additional feature. Some SCADA software support it, some do not.
Most of the plants are manufacturing multi products. When you have different products to
manufacture, you just have to load the recipe of the particular product.
Security is on facility people generally look for. You can allocate certain facilities or features to
the operator, process people, engineering dept and maintenance dept. for example operators
should only operate the system, he should not be able change the application. The engineers
should have access to changing the application. The engineers should have access to changing
the application developed.
Device Connectivity you will find there are hundreds of automation hardware manufacturer like
Modicon, Siemens, Allenbradley, ABB. Everybody has there own way of communication or we
can say they have their own communication protocol. SCADA software should have
connectivity to the different hardware used in automation. It should not happen that for Modicon
I am buying one software and for Siemens another one. The software like Aspic or Wonderware
has connectivity to almost all hardware used in automation.
Database Connectivity now a day’s information plays very important role in any business. Most
manufacturing units go for Enterprise Resource Planning or Management Information System.
Uses of SCADA
Production Department
● Real time production status: manufacturing status is updated in real time in direct
communication to operator and control device
● Production schedules: production schedules can be viewed and updated directly
● Production information management: production specific information is distributed to all
Quality Department
● Data integrity and quality control is improved by using a common interface
● It is an open platform for statistical analysis
● Consolidation of manufacturing and lab data
Maintenance Department
● Improved troubleshooting and de-bugging: direct connection to wide variety of devices,
displays improves troubleshooting reduces diagnostic/debugging time
● Plant can be viewed remotely. Notification can include pagers, e-mails and phones.
● Co-ordination between maintenance and management reduces unscheduled downtime.
Enterprise Information
● corporate information and real time production data can be gathered and viewed from
anywhere within operations
● User specific information ensures better informed decisions
● Data exchange with standard databases and enterprise systems provides integrated information
solutions
Engineering Department
● Integrated automation solutions reduce design and configuration time
● Common configuration platform offers flexibility for constant configuration in all areas
● Capable of connecting to wide variety of systems. Reduces start up time and system training
with industry proven open interfaces
Manufacturing Department
● Unscheduled down time is reduced due to swift alarm detection and event driven information
● Makes operations easier and more repeatable with its real time functionality
● Secured real time operation are maintained with windows
General Terminology
What is a Tag- a tag is a logical name for a variable in a device or local memory (RAM). Tags
that receive data from some external devices such as programmable logic controllers or servers
are refereed to as I/O tags. Tags that receive data internally from software are called memory
tags.
Analog Tags- store a range of values. EX temp, flow, density etc
Discrete tags- to store values such as 0 or 1. EX on/off status of a pump, valves, switches
etc.
System tags- store information generated while the software is running including alarm
info and system time and date.
String tags- are used to store ASCII strings a series of characters or whole word. The
max string length is 131 characters.
Touch links- allow the operator to input data into the system. EX. Operator may turn the value
on or off, enter a new alarm set point, run a complex logic script etc.
Touch push buttons-are used to create object link that immediately perform an operation when
clicked with the mouse or touched. These operations can be discrete value changes, action script
executions and show or hide window commands.
Colour links- are used to animate the line colour, fill colour or text colour of an object. Each of
these colour attributes can be made dynamic by defining a colour link for the attribute. The
colour attribute may be linked to the value of a discrete expression, analogue expression, discrete
alarm status or analog alarm status.
Visibility- used to control visibility of an object based on the value of discrete tag name or
expression.
Blink- used to make an object blink based on the value of the discrete tagname or expression.
Orientation- used to make an object rotate based on the value of a tagname /expression.
Disable- used to disable the touch functionality of objects based on the value of a tagname of
expression. Often used as a part of a security strategy.
Value display links- provides the ability to use text object to display the value of a discrete,
analog or string tagname.
Percent fill links- used to provide ability to vary the fill level of a filled shape according to the
value of an analog tagname or an expression that computes to an analog value.
Application script- are linked to entire applications and are used to start other applications,
create process simulation, calculate variables and so on: three types of application scripts are on
start up, while running, on shut down.
Window script- is linked to specific window. 3 types of window scripts are on show, while
showing, on hide.
Key script- touch pushbutton action scripts are similar to key scripts, except they are associated
with an object that you link to a touch link action pushbutton. 3 types are on key down, while
down, on key up.
Condition script- is linked to discrete tagname or expression that equates to true or false. You
can also use discrete expressions that contain analog tagnames. 4 types of scripts that you can
apply to a condition are on true, on false, while true, while false.
Data change script- are linked to a tagname and/or tagname field changes by a value greater
than a dead band that you defined for the tagname in the tagname dictionary.
Application security- to an application is optional. It provides the application developer with the
ability to control whether or not specific operators are allowed to perform specific functions
within an application Security is based on the concept of operator logging on to the application
and entering his user name and password and access level. For each operator access to any
protected function is granted upon verification of his password and access level.
Security Issues
The move from proprietary technologies to more standardized and open solutions together with
the increased number of connections between SCADA systems and office networks and the
Internet has made them more vulnerable to attacks. Consequently, the security of SCADA-based
systems has come into question as they are increasingly seen as extremely vulnerable to cyber
warfare/cyber terrorism attacks.
In particular, security researchers are concerned about:
the lack of concern about security and authentication in the design, deployment and
operation of existing SCADA networks
the mistaken belief that SCADA systems have the benefit of security through obscurity
through the use of specialized protocols and proprietary interfaces
the mistaken belief that SCADA networks are secure because they are purportedly
physically secured
the mistaken belief that SCADA networks are secure because they are supposedly
disconnected from the Internet
SCADA systems are used to control and monitor physical processes, examples of which are
transmission of electricity, transportation of gas and oil in pipelines, water distribution, traffic
lights, and other systems used as the basis of modern society. The security of these SCADA
systems is important because compromise or destruction of these systems would impact multiple
areas of society far removed from the original compromise. For example, a blackout caused by a
compromised electrical SCADA system would cause financial losses to all the customers that
received electricity from that source. How security will affect legacy SCADA and new
deployments remains to be seen.
Many vendors of SCADA and control products have begun to address these risks in a basic sense
by developing lines of specialized industrial firewall and VPN solutions for TCP/IP-based
SCADA networks. Additionally, application white listing solutions are being implemented
because of their ability to prevent malware and unauthorized application changes without the
performance impacts of traditional antivirus scans. Also, the ISA Security Compliance Institute
(ISCI) is emerging to formalize SCADA security testing starting as soon as 2009. ISCI is
conceptually similar to private testing and certification that has been performed by vendors since
2007. Eventually, standards being defined by ISA99 WG4 will supersede the initial industry
consortia efforts, but probably not before 2011.
The increased interest in SCADA vulnerabilities has resulted in vulnerability researchers
discovering vulnerabilities in commercial SCADA software and more general offensive SCADA
techniques presented to the general security community. In electric and gas utility SCADA
systems, the vulnerability of the large installed base of wired and wireless serial communications
links is addressed in some cases by applying bump-in-the-wire devices that employ
authentication and Advanced Encryption Standard encryption rather than replacing all existing
nodes.
SCADA as an asset
TYPICAL DETERIORATION CURVE FOR INFRASTRUCTURE ASSET
Practical Uses of SCADA
● SCADA used as a control mechanism for chemical plants, electricity generation, electric
power transmission, electricity distribution, district heating.
● Control mechanisms are described in Process Control.
●EPICS is an example of an open source software environment used to develop and implement
SCADA system to operate devices such as particle accelerators, telescopes and other large
experiments.
Advantages of SCADA System
1. A SCADA system is "normally" significantly cheaper than a DCS.
2. SCADA can continue operating even when telecommunication are temporarily lost.
3. SCADA systems allow a smaller number of operators to control a large number of
individual assets.
4. SCADA systems were designed to be used on large scale systems with remote assets
over a very large geographical area.
5. SCADA system improves operation, maintenance and customer service and provides
rapid response to emergencies.
6. It provides a high level of system reliability and availability.
Mid – Term ReportOn Behalf Of
6 Months Industrial TrainingAt
Prolific Systems and Automation Technology Pvt. Ltd. Noida
Submitted To: Submitted By:
Er. Krishan Arora Sourabh BansalLect. (EEE) B.Tech (EEE), 8th sem 6080709649