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ACKNOWLEDGEMENT

I would like to thank SOFCON INDIA PVT.LIMITED, AHMEDABAD for providing me

exposure to the whole SCADA & PLCs System. Id also like to thank Mr.Rohit Sher for their

enduring support and guidance throughout the training. I am very grateful to the whole

Control and Instrumentation Department for their support and guidance.

I am also very thankful to the workers and employees near the machineries and the library in

charge for their support to my training.

Youre sincerely,

Anurag Sharma

09EPFEC007

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CONTENTS

Abstract.1

Chapter 1:Automation..2

1.1 Advantage and Disadvantage of Automation......................................................3

1.2 Types of Automation4

1.2.1 Fixed type..4

1.2.2 Programmable type....4

1.2.3 Flexible type...4

Chapter 2: Programable logic controller.......................................................5

2.1 Features of PLCs.....6

2.2 PLC compared with other control systems ......9

2.3 Digital and analog signals...10

2.3.1 Example.........11

2.4 Programming ......11

2.5 Ladder Logic............12

2.5.1 Example of a Simple Ladder Logic Program ...... ..17

2.5.2 Program for Start/Stop of Motor ...19

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Chapter 3: Supervisory Control and Data Acquisition (SCADA)..24

3.1 Architecture ...........24

3.2. Functionality........27

3.3 Application Development........29

3.4 Evolution..........30

3.5 Engineering..........31

3.6 Potential benefits of SCADA...........31

4. Conclusion......................................................................................33

5. References..........................................................................................................34

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List of figure

Figure 2.1 Figure showing several input and output modules of a single Allen-Bradley

PLC...................................................................................................................6

Figure 2.2Block diagram of a PLC................7

Figure 2.3 Diagram Showing Energized input terminal X1.......8

Figure 2.4Diagram Showing Energized Output Y1.......9

Figure 2.5Diagram Showing motor start ckt and ladder program.17

Figure 2.6Diagram Showing Lamp Glows when at Input Switch is actuated..18

Figure 2.7Diagram Showing Start/Stop of Motor by PLC....20

Figure 2.8Diagram Showing Starting of Motor.....21

Figure 2.9 Diagram Showing Logic for Continuous Running of motor When Start Button is

released22

Figure 2.10Diagram Showing to Stop the Motor..............23

Figure 3.1Architecture of SCADA...24

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Abstract

An industrial SCADA & PLCs system is used for the development of the controls of

machinery. This report describes the SCADA & PLCs 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 paid to the industrial standards to which they

abide their planned evolution as well as the potential benefits of their use.

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CHAPTER 1

Automation

Automation is the use of machines, control systems and information technologies to optimize

productivity in the production of goods and delivery of services. The correct incentive for

applying automation is to increase productivity, and/or quality beyond that possible with

current human labor levels so as to realize economies of scale, and/or realize predictable

quality levels. The incorrect application of automation, which occurs most often, is an effort

to eliminate or replace human labor. Simply put, whereas correct application of automation

can net as much as 3 to 4 times original output with no increase in current human labor costs,

incorrect application of automation can only save a fraction of current labor level costs. In the

scope of industrialization, automation is a step beyond mechanization. Whereas

mechanization provides human operators with machinery to assist them with the muscular

requirements of work, automation greatly decreases the need for human sensory and mental

requirements while increasing load capacity, speed, and repeatability. Automation plays an

increasingly important role in the world economy and in daily experience.

Automation has had a notable impact in a wide range of industries beyond

manufacturing (where it began). Once-ubiquitous telephone operators have been replaced

largely by automated telephone switchboards and answering machines. Medical processes

such as primary screening in electrocardiography or radiography and laboratory analysis of

human genes, sera, cells, and tissues are carried out at much greater speed and accuracy by

automated systems. Automated teller machines have reduced the need for bank visits to

obtain cash and carry out transactions. In general, automation has been responsible for the

shift in the world economy from industrial jobs to service jobs in the 20th and 21st centuries.

The term automation, inspired by the earlier word automatic (coming fromautomaton), was not widely used before 1947, when General Motors established the

automation department. At that time automation technologies were electrical, mechanical,

hydraulic and pneumatic.

Between 1957 and 1964 factory output nearly doubled while the number of blue

collar workers started to decline.

http://en.wikipedia.org/wiki/World_economyhttp://en.wikipedia.org/wiki/World_economy

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1.1 Advantage and Disadvantage of Automation

Advantage:

Increased throughput or productivity.

Improved quality or increased predictability of quality.

Improved robustness (consistency), of processes or product.

The following methods are often employed to improve productivity, quality, or robustness.

Install automation in operations to reduce cycle time.

Install automation where a high degree of accuracy is required.

Replacing human operators in tasks that involve hard physical or monotonous work.

Replacing humans in tasks done in dangerous environments (i.e. fire, space,

volcanoes, nuclear facilities, underwater, etc.)

Performing tasks that are beyond human capabilities of size, weight, speed,

endurance, etc.

Economy improvement: Automation may improve in economy of enterprises, society

or most of humanity. For example, when an enterprise invests in automation,

technology recovers its investment; or when a state or country increases its income

due to automation like Germany or Japan in the 20th Century.

Reduces operation time and work handling time significantly.

Frees up workers to take on other roles.

Provides higher level jobs in the development, deployment, maintenance and running

of the automated processes.

Disadvantages:

Security Threats/Vulnerability: An automated system may have a limited level of

intelligence, and is therefore more susceptible to committing errors outside of its

immediate scope of knowledge (e.g., it is typically unable to apply the rules of simplelogic to general propositions).

Unpredictable/excessive development costs: The research and developmentcost of

automating a process may exceed the cost saved by the automation itself.

High initial cost: The automation of a new product or plant typically requires a very

large initial investment in comparison with the unit cost of the product, although the

cost of automation may be spread among many products and over time.

http://en.wikipedia.org/wiki/Product_%28business%29http://en.wikipedia.org/wiki/Planthttp://en.wikipedia.org/wiki/Planthttp://en.wikipedia.org/wiki/Product_%28business%29

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1.2Types of Automation:

1.2.1 Fixed type: A process using mechanized machinery to perform fixed and repetitive

operations in order to produce a high volume of similar parts.

Typical features:

Suited to high production quantities.

High initial investment for custom-engineered equipment.

High production rates.

Relatively inflexible in accommodating product variety.

1.2.2 Programmable automation: It is a compact controller that combines the features of a

pc based control system with that of typical PLC.

Typical features:

High investment in programmable equipment.

Lower production rates than fixed automation.

Flexibility to deal with variations and changes in product

configuration.

Most suitable for batch production.

Physical setup and part program must be changed between jobs

(batches).

1.2.3 Flexible type: System is capable of change in over from one job to next with little

lost time between jobs.

Typical features:

High investment for custom-engineered system.

Continuous production of variable mixes of products.

Medium production rates.

Flexibility to deal with soft product variety.

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CHAPTER 2

Programmable Logic Controller

A Programmable Logic Controller, PLC, or Programmable Controller is a digital computer

used for automation of industrial processes, such as control of machinery on factory assembly

lines. 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.

PLC and Programmable Logic Controller are registered trademarks of the Allen-

Bradley Company.

SCADA is widely used in industry for Supervisory Control and Data Acquisition of

industrial processes; SCADA systems are now also penetrating the experimental physics

laboratories for the controls of systems such as cooling, ventilation, power distribution, etc.

More recently they were also applied for the controls of smaller size particle detectors such as

the L3 moon detector.

SCADA systems have made substantial progress over the recent years in terms offunctionality, 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. .

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2.1 FEATURES OF PLCs

Figure 2.1 Figure showing several input and output modules of a single Allen-Bradley 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

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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.

2.1.1 Wiring in a PLC

Fig.2.2Block diagram of a PLC

2.1.2 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

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terminal. An indicating LED on the front panel of the PLC gives visual indication of an

"energized" input:

Fig. 2.3 Diagram Showing Energized input terminal X1

2.1.3 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.

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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

Fig 2.4 Diagram Showing Energized Output Y1 port.

2.2 PLC COMPARED WITH OTHER CONTROL SYSTEM

PLCs are well-adapted to a certain 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 systemwould 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 in ladder logic

(or function chart) notation. 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. For high volume or very simple fixed automation tasks, different techniques are used.

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A microcontroller-based design would be appropriate where hundreds or thousands of

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

input/output hardware) can be spread over many sales, and where the end-user would not

need to alter the control. Automotive applications are an example; millions of units are built

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

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

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

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

"proportional, integral, derivative" or "PID controller." A PID loop could be used to control

the temperature of a manufacturing process, for example. Historically PLCs were usually

configured with only a few analog control loops; where processes required hundreds or

thousands of loops, a distributed control system (DCS) would instead be used. However, as

PLCs have become more powerful, the boundary between DCS and PLC applications has

become less clear-cut.

2.3 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). Pushbuttons, limit switches, and photoelectric sensors are

examples of devices providing a discrete signal. Discrete signals are sent using either voltageor 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.

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2.3.1 Example

As an example, say the 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 (tank

empty and tank full). The PLC uses a digital output to open and close the inlet valve into the

tank.

If both float switches are off (down) or only the 'tank empty' switch is on, the PLC

will open the valve to let more water in. Once the 'tank full' switch is on, the PLC will

automatically shut the inlet to stop the water from overflowing. If only the 'tank full' switch is

on, something is wrong because once the water reaches a float switch, the switch will stay on

because it is floating, thus, when both float switches are on, the tank is full. Two float

switches are used to prevent a 'flutter' (a ripple or a wave) condition where any water usage

activates the pump for a very short time and then deactivates for a short time, and so on,

causing the system to wear out faster.

An analog system might use a load cell (scale) that weighs the tank, and an adjustable

(throttling) valve. The PLC could use a PID feedback loop to control the valve opening. The

load cell is connected to an analog input and the valve is connected to an analog output. This

system fills the tank faster when there is less water in the tank. If the water level drops

rapidly, the valve can be opened wide. If water is only dripping out of the tank, the valve

adjusts to slowly drip water back into the tank.

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. Backup and

maintenance methods can make a real system very complicated.

2.4 PROGRAMMING

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, and then downloaded by a direct-connection cable or over a network

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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.

2.5 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 awide 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 featuresthat 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.

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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.

2.5.1 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.

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2.5.1.1Generally Used Instructions & symbol For PLC Programming

2.5.1 .1.1 Input Instruction

--[ ]-- This Instruction is Called XIC or Examine If Closed.

i.e.; 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 XIO or Examine If Open

i.e.; 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.

2.5.1.1.2 Output Instruction

--( )-- This Instruction Shows the States of Output.

i.e.; 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.

2.5.1.1.3 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

| |

|--[ ]--|

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Z

The above realizes 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

2. 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.

2.5.1.2 More practical examples

Example-1

------[ ]--------------[ ]----------------O---

Key Switch 1 Key Switch 2 Door Motor

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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

2.5.1.3 Example with PLC

Consider the following circuit and PLC program:

-------[ ]--------------( )---

run motor

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Fig 2.5 Diagram Showing motor start circuit and ladder program.

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 an

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 coilnamed "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:

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2.5.1.4 Lamp Glows when at Input Switch is Actuated

Fig 2.6 Diagram Showing Lamp Glows when at Input Switch 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

behaviour of a control system. Since the PLC is a programmable device, we can alter its

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behaviour 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.

2.5.2 Programming For Start/Stop of Motor by PLC

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

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Fig 2.7 Diagram Showing Start/Stop of Motor by PLC.

The pushbutton switch connected to input X1 serves as the "Start" switch, while the switch

connected to input X2 serves as the "Stop." Another contact in the program, named Y1, uses

the output coil status as a seal-in contact, directly, so that the motor contactor will continue to

be energized after the "Start" pushbutton switch is released. You can see the normally-closed

contact X2 appear in a coloured block, showing that it is in a closed ("electrically

conducting") state.

2.5.2.1 Starting of Motor

If we were to press the "Start" button, input X1 would energize, thus "closing" the X1 contact

in the program, sending "power" to the Y1 "coil," energizing the Y1 output and applying 120

volt AC power to the real motor contactor coil. The parallel Y1 contact will also "close," thus

latching the "circuit" in an energized state:

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Fig 2.8 Diagram Showing Starting of Motor.

2.5.2.2 Logic for Continuous running of motor when Start Button is Released

Now, if we release the "Start" pushbutton, the normally-open X1 "contact" will return to its

"open" state, but the motor will continue to run because the Y1 seal-in "contact" continues to

provide "continuity" to "power" coil Y1, thus keeping the Y1 output energized:

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Fig 2.9 Diagram Showing Logic for Continuous Running of motor When StartButton is

released

2.5.2.3 To Stop the Motor

To stop the motor, we must momentarily press the "Stop" pushbutton, which will energize the

X2 input and "open" the normally-closed "contact," breaking continuity to the Y1 "coil:"

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Fig 2.10 Diagram Showing to Stop the Motor.

When the "Stop" pushbutton is released, input X2 will de-energize, returning "contact" X2 to

its normal, "closed" state. The motor, however, will not start again until the "Start"

pushbutton is actuated, because the "seal-in" of Y1 has been lost:

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CHAPTER 3

Supervisory Control and Data Acquisition (SCADA)

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 not only in industrial processes: e.g. steel making, power

generation (conventional and nuclear) and distribution, chemistry, but also in some

experimental facilities such as nuclear fusion. The size of such plants range from a few 1000

to several 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 100 K:

we know of two cases of near to 1 M I/O channels currently under development.

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.

3.1 ARCHITECTURE

This section describes the common features of the SCADA products that have been evaluated

at CERN in view of their possible application to the control systems of the LHC detectors [1],

[2].

Fig 3.1 Architecture of SCADA

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3.1.1 Hardware Architecture

One distinguishes two basic layers in a SCADA system: 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. PLCs, are connected to the data servers either

directly or via networks or field buses 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. The data servers and client stations are NT platforms but for many

products the client stations may also be W95 machines. .

3.1.2 Communications

3.1.2.1 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.

3.1.2.2 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 at

CERN, both Profibus and World flip are supported but CANbus often not [3]. 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.

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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

toolkit is provided for this.

3.1.3 Interfacing

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. OPC has been evaluated

by the CERN-IT-CO group [4].

The products also provide

1. An Open Data Base Connectivity (ODBC) interface to the data in the archive/logs,

but not to the configuration database,

2. An ASCII import/export facility for configuration data,

3. 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).

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.

3.1.4 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

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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).

3.1.5 Redundancy

The products often have built in software redundancy at a server level, which is normally

transparent to the user. Many of the products also provide more complete redundancy

solutions if required.

3.2 FUNCTIONALITY

3.2.1 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.

3.2.2 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.

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3.2.3 Trending

The products all provide trending facilities and one can summarize the common capabilities

as follows:

1. The parameters to be trended in a specific chart can be predefined or defined on-line

2. 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)

3. Real-time and historical trending are possible, although generally not in the same

chart

3.2.4 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.

3.2.5 Logging/Archiving

The terms logging and archiving are often used to describe the same facility. However,

logging can be thought of as medium-term storage of data on disk, whereas archiving is long-

term storage of data either on disk or on another permanent storage medium. Logging is

typically performed on a cyclic basis, i.e., once a certain file size, time period or number of

points is reached the data is overwritten. Logging of data can be performed at a set frequency,

or only initiated if the value changes or when a specific predefined event occurs. Logged data

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can be transferred to an archive once the log is full. The logged data is time-stamped and can

be filtered when viewed by a user. The logging of user actions is in general performed

together with either a user ID or station ID. There is often also a VCR facility to play back

archived data.

3.2.6 Report Generation

One can produce reports using SQL type queries to the archive, RTDB or logs. Although it is

sometimes possible to embed EXCEL charts in the report, a "cut and paste" capability is in

general not provided. Facilities exist to be able to automatically generate, print and archive

reports.

3.2.7 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.

3.3 APPLICATION DEVELOPMENT

3.3.1 Configuration

The development of the applications is typically done in two stages. First the process

parameters and associated information (e.g. relating to alarm conditions) are defined through

some sort of parameter definition template and then the graphics, including trending and

alarm displays are developed, and linked where appropriate to the process parameters. The

products also provide an ASCII Export/Import facility for the configuration data (parameter

definitions), which enables large numbers of parameters to be configured in a more efficient

manner using an external editor such as Excel and then importing the data into the

configuration database.

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However, many of the PC tools now have a Windows Explorer type development

studio. The developer then works with a number of folders, which each contains a different

aspect of the configuration, including the graphics.

The facilities provided by the products for configuring very large numbers of

parameters are not very strong. However, this has not really been an issue so far for most of

the products to-date, as large applications are typically about 50K I/O points and database

population from within an ASCII editor such as Excel is still a workable option.

On-line modifications to the configuration database and the graphics are generally possible

with the appropriate level of privileges.

3.3.2 Development Tools

The following development tools are provided as standard:

1. A graphics editor, with standard drawing facilities including freehand, lines, squares

circles, etc. It is possible to import pictures in many formats as well as using

predefined symbols including e.g. trending charts, etc. A library of generic symbols is

provided that can be linked dynamically to variables and animated as they change. It

is also possible to create links between views so as to ease navigation at run-time.

2. A data base configuration tool (usually through parameter templates). It is in generalpossible to export data in ASCII files so as to be edited through an ASCII editor or

Excel.

3. A scripting language

4. An Application Program Interface (API) supporting C, C++, VB

3.4 EVOLUTION

SCADA vendors release one major version and one to two additional minor versions once per

year. These products evolve thus very rapidly so as to take advantage of new market

opportunities, to meet new requirements of their customers and to take advantage of new

technologies.

As was already mentioned, most of the SCADA products that were evaluated

decompose the process in "atomic" parameters to which a Tag-name is associated. This is

impractical in the case of very large processes when very large sets of Tags need to be

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configured. As the industrial applications are increasing in size, new SCADA versions are

now being designed to handle devices and even entire systems as full entities (classes) that

encapsulate all their specific attributes and functionality. In addition, they will also support

multi-team development.

As far as new technologies are concerned, the SCADA products are now adopting:

Web technology, ActiveX, Java, etc.

OPC as a means for communicating internally between the client and server modules.

It should thus be possible to connect OPC compliant third party modules to that SCADA

product.

3.5 ENGINEERING

Whilst one should rightly anticipate significant development and maintenance savings by

adopting a SCADA product for the implementation of a control system, it does not mean a

"no effort" operation. The need for proper engineering cannot be sufficiently emphasized to

reduce development effort and to reach a system that complies with the requirements, that is

economical in development and maintenance and that is reliable and robust. Examples of

engineering activities specific to the use of a SCADA system are the definition of:

1. A library of objects (PLC, device, subsystem) complete with standard object

behaviour (script, sequences, ...), graphical interface and associated scripts for

animation,

2. Templates for different types of "panels", e.g. alarms,

3. Instructions on how to control e.g. a device ...,

4. A mechanism to prevent conflicting controls (if not provided with the SCADA),

alarm levels, behaviour to be adopted in case of specific alarms.

3.6 POTENTIAL BENEFITS OF SCADA

The benefits one can expect from adopting a SCADA system for the control of experimental

physics facilities can be summarized as follows:

1. A rich functionality and extensive development facilities. The amount of effort

invested in SCADA product amounts to 50 to 100 p-years!

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2. The amount of specific development that needs to be performed by the end-user is

limited, especially with suitable engineering.

3. Reliability and robustness. These systems are used for mission critical industrial

processes where reliability and performance are paramount. In addition, specific

development is performed within a well-established framework that enhances

reliability and robustness.

4. Technical support and maintenance by the vendor.

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CONCLUSION

SCADA is used for the constructive working not for the destructive work using a SCADA

system for their controls ensures a common framework not only for the development of the

specific applications but also for operating the detectors. Operators experience the same "lookand 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

Note: this article is based on a very similar one that has been published in the Proceedings

of the 7th International Conference on Accelerator and Large Experimental Physics Control

Systems, held in Trieste, Italy, 4 - 8 Oct. 1999.[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 Field buses 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] R.Barillere et al., "Results of the OPC Evaluation done within the JCOP for the Control of

the LHC Experiments", Proceedings of the 1999 International Conference on Accelerator and

Large Experimental Physics Control Systems, Trieste, 1999, p.511.