CPU•Control unit•ALU•Registers•Ports•Other auxiliary units

Output devices•Monitor•Printer•Other devices

Input devices•Keyboard•Mouse•Other devices

Memory•RAM (SRAM, DRAM)•ROM (PROM, EPROM, EEPROM)•Floppy disk•Hard disk•CD ROM

input output

Data out Data in

“A computer is an electronic device for the fast and accurate processing of data/information under the control of a stored logical sequence of instructions called a software program.” All computers, regardless of their size, have the similar general design which essentially consist of CPU, memory, I/O devices, communication slots and ports, electronic circuits and a clock.

Application Software

System Hardware (Processor, Memory, Cards, etc. etc..)

Drivers

Operating System•IPC•Multi-tasking•Multi-threading

External devices and Units

“An operating system is a system program that control the hardware and other software of the computer and when it is opened it brings the computer system into a mode from where it is easier to run other applications. OS

provides an ‘abstraction layer’

between the application software and the low level hardware by freeing the programmer from any concern about the details of the underlying hardware of the computer. In summary, the OS manages the resources. The resources are application software, data, files, information and peripheral hardware such as floppy drive, hard drive, CD drive, printer, scanner, etc.”

DOS

RESOURCES

DOS

DOS

DOS

DOS

RESOURCE-1

DOS

RESOURCE-2

DOS

RESOURCE-n

DOS

NetworkNetwork

Network

(a)

(b)

The need for Distributed Operating System (DOS) arises only when the computer resources are apart from each

other i.e., when they are found to be geographically distributed.

Preprocessor

Compiler

Assembler

Link editor

Source code in High-level language

Target language (Could be Hexadecimal code)

Object codeLibraries

MACHINE LANGUAGE (Executable code)

To write a program a high-level programming language is necessary. Compiler is a program that reads a program written in one high-level computer language, called the source language, and translates it into an equivalent program in another language, called the target language. The target language is then converted to object code by the assembler.

The ‘MATLAB Command Window

MATLAB is a software tool that stands for Matrix Laboratory. It provides facilities like system analysis, matrix computation, signal processing and graphics.

MATLAB Editor/Debugger

MATLAB window used for saving the m-file in the directory.

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

A sign wave of 50 Hz generated by using MATLAB simulation software.

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

A signal containing fundamental frequency of 50 Hz and superimposed by a third harmonic component of 10% that of fundamental. Generated by using MATLAB simulation software.

-1 -0.5 0 0.5 1 1.5 2 2.5 3 -10

0

10

20

30

40

50

60

A plot of the following function. The plot was obtained by using MATLAB program.

5)7.0(03.0

1

)4.0(02.0

1)(

22

tttf

0 20 40 60 80 100 120 140 160 180 200-1

-0.5

0

0.5

1Signal

0 20 40 60 80 100 120 140 160 180 2000

20

40

60

80

100DFT of the Signal

(a) The signal at hand; (b) Its DFT

MATLAB provides powerful interactive plotting capabilities that allows to visualize data, equations and results.

SERVER(Central database)

Client-1 Client-3Client-2

Operating System

Client-server (CS) architecture is an extension of the centralised configuration. Data is mostly processed in clients. Client-server conformant application software can give greater viability to distributed processing.

APPLICATION LAYER

PRESENTATION LAYER

SESSION LAYER

TRANSPORT LAYER

NETWORK LAYER

DATALINK LAYER

PHYSICAL LAYER

APPLICATION LAYER

PRESENTATION LAYER

SESSION LAYER

TRANSPORT LAYER

NETWORK LAYER

DATALINK LAYER

PHYSICAL LAYER

MEDIUM

OSI MODEL

Data path

Device-1 Device-2

A B

Computer network is a network of computers. The network is also called data network. Traditionally, any kind of data communication between the computers is governed by a reference model called the ISO/OSI RM (International Standards Organization/Open System Interconnection Reference

Model). The ISO/OSI RM is a specification guidelines based upon which the computer communication systems have been developed and designed. The guideline defines the essential services that are required for achieving reliable and faithful data communications. The specification constitute a collection of services, which have been partitioned into seven layers.

4-20mA signal

S=sensorA=actuator

CONSOLE

CENTRAL CONTROLLER

Junction Box(Analogue (Multiplexer)

SA

SA

Other I/O devices

As far as communication between the controller and the I/O devices are concerned, all control implementations are broadly comes under three categories.

Centralised controlDistributed controlHybrid control

Centralized control scheme, a conventional one, has a central processing unit, called central controller. The central controller communicates with a number of field devices through parallel link

Valve

Valve

Pressure sensor

Level alarm system

Temperature sensor

Gas detector

MotorTemperature sensorEncoder

Host Computer(Development tool)

Display

Display

another plant

Pump

PROCESS(plant)

A DCS system is simply a network of controllers. The network thus formed is referred to as control network. The entire task which was residing in a central controller is by far divided among many controllers, resulting in a smooth execution of the whole control process.

CPU(s)I/Oport

networkcommunication port

Sensing andActuatingdevices

M E M O R Y (ROM and RAM )

protocolapplication program

network configuration

application buffer

network buffer Tranceiverpower supplyclock

Network

The heart of a DCS is node. A node consists of a microprocessor to execute task, RAM/PROM/EEPROM for storage of data/code/protocol etc., Ports for interfacing with the field devices (e.g., sensors, actuators, etc.), and transceiver to interface with other nodes to form the control network. A node can be called a smart device as it is capable of executing the task processing signal, data, information and message at the field-level or the device level.

NODE

other devicesS

Aswitch

control network

NODE

other devicesS

Aswitch

multiple I/O interactions

I/O interface I/O interfacelocal control loop

networked control loop

Real-time systems are usually reactive systems that are in continual interaction with their environments. Control systems for real-time applications are characterised by their ability to support strong time constraints. Control loops can be formed locally for reducing the network traffic.

Star-ring (token passing)

peer-to-peer (linear)

= NODE

Tree (hierarchical)

2N1N

4NnN3N

1N

1N

5N

6N

7N

8N

3H

2N

3N

4N

nN

2N3N

4N

Star (master-slave)

1N

3N

2N

4NnN

1H

1H

2H1H

Messages are transmitted from one node to the other through the network that complies with specific topology.

Control Network (Hardware)

Target application platforms(Plant/Process/System)

DCS

Operating SystemsSoftware toolProgramming Language

Host Computer

Development Tools

Controllers

The design and implementation of DCS systems consider three major elements; Target application platform such as process/plant/system. Electronics such as processor, transceiver, communication

media, I/O interfaces, etc. Development tools such as host computer with OS and application software

 

sensoractuator switch gateway

Node-3Node-4

Node-2 Node-5

Node-7

Node-1

Optional Monitoring and

Supervisory controllerHost Processor

Code development tool

Network management tool

intelligent device

(PLC, PC, Controller etc.)

Channel/Network

router node-6

OS

A typical fieldbus-based Distributed Control System scenario

A

A

P

D

N

T

S

P

Redundant layers

Management layer being defined

D

P

ISO/OSI Layers Fieldbus Layers

The fieldbus protocol does not include all the services of all the layers of ISO/OSI model. This is an essential requirement of almost all control networking systems. The reduced version of the ISO/OSI layers aid strong real-time requirements.

System study

Control Problem Analysis

Task segmentation

Device identification

Virtual design

Device validation

Virtual connection

DCS validation

Modification and refinement

Scalability, Extendibility Issue

On-line testing

Refinement and modification

Testing

Configuration (logical binding)

Integration

Individual testing

Individual installation

Application code development

System study

Control Problem Analysis

Task segmentation

Device identification

Virtual design

Device validation

Virtual connection

DCS validation

Modification and refinement

System study

Control Problem Analysis

Task segmentation

Device identification

Virtual design

Device validation

Virtual connection

DCS validation

Modification and refinement

Scalability, Extendibility Issue

On-line testing

Refinement and modification

Testing

Configuration (logical binding)

Integration

Individual testing

Individual installation

Application code development

Scalability, Extendibility Issue

On-line testing

Refinement and modification

Testing

Configuration (logical binding)

Integration

Individual testing

Individual installation

Application code development

In order to realize fieldbus-based reliable DCS drawn upon representative target platforms the design methodology involves problem identification or specification, segmentation or decentralisation, development and testing. Regardless of the system complexity, in the DCS the stages involved in the design and development process are shown in the figure.

SCADA COMPUTERS

Distributed IntelligentController (Indistrial PC)

Distributed Fieldbus Network

FIELDBUS BRIDGE

nn nn

Distributed intelligent Controller(Industrial PC)

Internet

Remote PLC

SA

S S SA A

nodes

Sensors, Actuators

LAN NETWORK S

A typical integration of data and control network for monitoring and control of target applications