HPCL Project report

A STUDY OF ANALYSERS, PROGRAMMABLE LOGIC CONTROLLERS, DISTRIBUTED CONTROL SYSTEMS AND DATA COMMUNICATION

1. INTRODUCTION

Hindustan Petroleum Corporation Limited (HPCL) is a Global Fortune 500 company in

the Energy sector. HPCL has two refineries located in Mumbai (West Coast) and Visakh

(East Coast) with capacities of 5.5 MMTPA and 7.5 MMTPA respectively, churning out

a wide range of petroleum products. and over 300 grades of lubricants, specialties and

greases as per BIS standard.

HPCL has successfully contributed close to 20% of India's total refining requirements. Over the

years HPCL's capacity of production has expanded massively through various up gradation

initiatives.

The refineries, known for the full utilization of capacity and world class performance are

the foundations of HPCL's successful journey towards meeting India's energy requirements.

Hindustan Petroleum Corporation (HPCL) came into being in mid 1974 after take over and

merging of erstwhile Esso and Lube India undertakings.

Catlex was taken over by government of India in 1976 and subsequently merged with HPCL.

Hindustan Petroleum Corporation Limited thus emerged after merging Refining/Marketing

facilities of ESSO and CALTEX.

Hindustan Petroleum Corporation Limited today is the second largest integrated oil company in

India playing a significant role in the nation’s economic development and growth. against the

backdrop of economic liberalization,

HPCL is consistently improving its existence by strengthening its infrastructural facilities as

well as diversifying upstream and downstream into exploration and production and power and

petrochemicals and horizontally into LNG sector.

Page | 1DEPARTMENT OF ECE, GITAM UNIVERISTY


HPCL produces the entire range of petroleum products and serves all sectors of the economy-

industry, agriculture, transport, domestic, public utilities and also major consumers like the

railways, power plants, defense, fertilizer plants, etc.;

Visakh refinery performance had been consistently “excellent” over the years. The major

performance indicators are crude thruput, total distillate, fuel and loss and implementation of

ENCON and environmental projects.

1.1 Origin and growth of HPCL-VR

Commissioned in 1957 as Catlex oil refinery India limited (CORIL). First oil refinery on the East

Coast and the major industry in the city of Visakhapatnam, Andhra Pradesh.

Installed capacity of 0.65 Million Metric Tones per Annum {MMTA} in 1957 for refining of

crude oil into petroleum products [13200 bbl/day]. CORIL was taken over by the government of

India and merged with HPCL in 1978.

1.2 Refinery Overview

Visakh refinery is fuels based refinery generating major products of mass consumption like

petrol, diesel and kerosene. Hence, crude meeting general purpose characteristics can be

processed with this refinery configuration. Visakh refinery can process crude from Prussian gulf

under non-bituminous category, bituminous crude (crude yielding bitumen, used for paving

road).

The crude processed at refinery include



CRUDE COUNTRY

Kuwait Kuwait

Dubai UAE

Ummshaif UAE

Upper zakum UAE

Murban Saudi Arab

Arab medium Saudi Arab

Iran mix Iran

Lavan Blend Iran

Barash Lt Iran

Products And Treatment Facilities

S.NO Process unit Capacity (in MMPA)

1 CDU-I 1.5

2 CDU-II 3.0

3 CDU-III 3.0

4 BBU 0.225

5 VBU 1.0

6 FCCU-I(R) 0.95

7 FCCU-II 0.60

8 DHDS 1.8

9 PRU 0.1


Table-1 crude export countries

Table-2 Capacity of various processing units


Legend:

CDU: Crude Distillation Unit FCCU : Fluidized Catalytic Cracking

DHDS: Diesel Hydro De-Sulphurization Unit VBU : Vis Breaker Unit

BBU : Bitumen Blowing Unit PRU : Propylene Recovery Unit

Products:

S.NO DAILY PRODUCTION CAPACITY(in tones)

1 Crude processing 22500

2 LPG 610

3 Propylene 100

4 Sulphur 17+65

5 Diesel 7800

6 Naphtha 2150

7 LSHS 1790

8 Fuel oil 3500


Table-3 Daily Production capacity of various products


Treatment Units :

DHDS:Diesel Hydro De-Sulphurization Unit:1.8 MMPTA

LPG Amine Treatment Unit

LPG, ATF and Petrol Merox Units Amine Regeneration Unit

Environmental Control Facilities:

Sulphur Recovery Units: 3 no. [2 Locate Technology of Clauss process]

Sour water striping Units: 2 no.

Effluent Treatment Plants: 4 no.

CO Boilers: 2 no.



2. CONFIGURATION OF REFINERY

Visakh Refinery is being operated under the following major units:

Process Units

Treating Units

Power and utilities

Oil movement and storage units

Environment related units

2.1 Process UnitThe Process unit consists of three units:

1. CDU 2.FCCU 3.PRU

Crude Distillation UnitCDU consists of two sections:

Atmos section

Vacuum section

Atmos section:

Crude oil is first preheated from 30-1250c and pressure about 10kg/cm2 enters the Desalter. The

salts from crude are removed in the desalter units. The desalted crude is then boosted to a

pressure of 30-35kg/cm2, pre-heated to around 3600c.

The oil is allowed into the flash zone of atmos distribution column and the product to stripper

with steam to strip off the lighter products. The over head-vapors of the atmos column are

condensed in a series of conductors and the liquid in the receiver.



Heavy Naphtha, kerosene / ATF & Diesel product are withdrawn as side steams and stripped off

as lighter ends with supper heater MP steam in the respective strippers. The bottom stream in

atmos column is called RCO.

Products: Fuel Gas, LPG, Light-Naphtha, Heavy-Naphtha, kerosene, diesel & Reduced Crude

Oil.

Vacuum section:

Hot reduced crude oil from atmospheric column bottom is heated in a vacuum to 380oc and

introduced into the flash zone of vacuum column. The stop distillate out is withdrawn first.

The hydrocarbon vapors rising in the column are condensed into Heavy Vacuum Gas Oil

(HVGO) and Light Vacuum Gas Oil (LVGO). VGO is feed to FCCU as feed. The bottom

product of vacuum column is vacuum residue. The vacuum in the column is maintained by a

multistage ejector system.

Products: LVGO and the HVGO obtained are fed to FCCU, the combination of Short-Residue

and the slop cut forms the fuel oil which is consumed by the refinery.

Vis Breaking Unit (VBU)

Vacuum reside from either CDU I II or III or storage is received in visbreaking feed surge drum.

It operates at a pressure which is floating on main fractioning pressure visbreaking feed @ 5.0

kg/cm2g, 1200c – 1600c from surge drum is pumped by visbreaking feed charge pump which are

of screw type to a pressure of 7.6 kg/cm2g.

It is then heated in visbreaking tar exchange to 3200c by visbreaking crude is then routed to

heater through booster pumps @ 5.8kg/cm2g preheated visbreaker feed entries both passes of

visbreaker heater under individual pass.



Control visbreaker heater is a two-pass single shell heater with bridge wall type configuration

turbulizing water (BFKL) is injected to both the passes at a point where visbreaking reaction

starts. Fuel gasses heat visbreaker feed to 4550c (4700c) Residual heat recovered by superheating

LP & MP steam. Gas oil quench works primarily by vaporization quench effluent entries main

fractionators @ 4250c and 7 kg/cm2g where it is separated into visbreaker tar or fuel oil as side

stream product and naphtha and gas as overhead product.


Fig-2.1 Crude distillation unit


Bitumen Blowing Unit (BBU)

The unit normally receives hot vacuum residue directly from vacuum unit. The feed is cooled to

about 2320c in a stream generator before entering the bitumen converter. In bitumen converter

the vacuum residue is blown with air, since the reaction exothermic, the heat evolved has to be

removed.

This is done injected steam into the reactor at the top. Heat is recovered from bitumen leaving

converter bottom by generating steam and the bitumen is further trim cooled before sending to

storage.

The hydrocarbon vapors steam and unreacted air leave the converter top to water quench drum

where hydrocarbons are condensed along with some water. Hydrocarbon layer is sent to slop oil

whereas water sent to waste water treatment plant (WWTP) after separation of same in the

settler.

Fluidized Catalytic Cracking Unit (FCCU)

Vacuum Gas Oil from vacuum unit and recycle streams are pumped to raw oil furnace for

preheating the fresh feed.

This fresh feed is mixed with regenerated catalyst and enters the reactor at the base of riser

where they are vapourized and raised to the reactor temperature by the hot catalyst.

The mixture of oil, vapour and catalyst travels up the riser into reactor. The gas oil commences

to crack immediately when it contact the hot catalyst in the riser and continues until the oil

vapour is disengaged from the catalyst in the reactor.

The cracked products in vapour form continue through the reactor vapour line to fractionators.

The catalyst stripper surrounds the upper portion of the reactor passes around the reactor grid and

into the stripper, where if flows over baffles counter current to the rising stripping steam,

displaces oil vapours to the reactor.

Coke is deposited on the circulation catalyst in the reaction zone. The fuel gas leaving the top of

the regenerator goes to co-boilers where super heat is produced.



The regenerated catalyst is recycled with the incoming feed to the reactor. Vapours from reactor

are sending to Fractionators section where they are fractionated into recycle gas oil which is

returned to the reactor and produces Clarified Oil, Cycle Oil, Motor Sprint (Petrol), and Gas

products.

This is achieved by first sending the reactor products to fractionators where recycled gas oil and

clarified oil are taken as bottom products, cycle oil as side draw off and unstabilised motor sprint

and gas as overhead products.

The overhead gas is compressed and liquefied and separated from the separator is scrubbed with

unstabilised motor sprint in an absorber to recover the C3 &C4 in it.


Fig 2.2 Fluidized Catalytic Cracking Unit


The liquids form the separator and the absorbers are stripped off ethane and the gas stripped off

is recycled back to the gas compressor and liquefaction system to recover C3’s and C4’s carried

with the stripped gases. The liquid form stripper bottom is send to a Debutanizers where LPG is

taken as overhead product and stabilized MS as bottom product.

Products: Fuel Gas, Cracked LPG, Cracked Gasoline, Cracked Naphtha, Diesel component

[Light Cyclic Oil (LCO), Heavy Cyclic Oil (HCO), Clarified Oil, Low Sulphur Heavy Stock

(LSHS) Used as fuel for Industries and boilers from low sulphur crude processing. Also used in

Ships, Jute Batch Oil, Wash Oil-B, Propylene.

Propylene Recovery Unit (PRU )

The Propylene Recovery Unit is defined to recover Propylene from Cracked LPG, which is one

of the product streams of Fluidized Catalytic Cracking Unit (FCCU). Cracked LPG is a mixture

of Propane, Propylene, and Butane with some traces of C2 & C5 Hydrocarbons.

The unit is designed to process about 1,00,000TPA of cracked LPG produced at FCCU-I & II

and to recover 22,000TPA of Propylene. The process consists of four steps. In the first step, the

feed to unit i.e., Cr. LPG is prepared by draining out the traces of caustic carryover.

In the second step Cracked LPG is separated into C3’s and C4’s in a distillation column

consisting of 55 trays. C3’s being lighter is recovered from the column top.

In the third step, the C3’s are again separated into propylene and propane in the second

distillation column consisting of 98 trays. Propylene being lighter is recovered from the top of

the column. In the fourth step, the Propylene recovered is subjected to chemical treatment with a

mixture of Mono Ethanol Amine (MEA) and Caustic, then water washed and passed through a

mechanical coalesce to knock off moisture to meet the following specifications:



Purity : 95 %

Water : NIL

Total Sulphur : 5 ppm

The bottom products of the first column consisting of Butane & Butylenes along the bottom

product of second column consisting Propane are routed to LPG Spheres. On special Propylene

is routed to its spheres and off- Special is routed to LPG spheres.

2.2 Treating Units

1. Merox Unit 2. Diesel Hydro De-Sulphurisation

Merox Unit

The LPG containing is treated here and the sulphur is removed from it. The Kerosene’s flash

point is increased in this unit and the sore water containing gas is treated here and the water is

recycled for usage.

LPG Merox Units

While separate facilities are provided for straight run and cracked LPG’S for extraction, a

common facility is provided for caustic generation. After Amine washing LPG enters the caustic

pre-wash tower, the purpose of which is to remove traces of hydrogen sulphide.

The LPG extractor which is perforated tray column. In this type of extraction column, caustic

soda containing dispersed Merox catalyst is would lead to caustic soda entertainment. The LPG

is introduced near the bottom of the column below the first perforated tray. LPG, with

mercaptans, is transferred to the caustic solution forming sodium mercaptides.

The LPG then goes in to the LPG settler. The spent caustic carried over from the LPG extractor

decants and treated LPG is recovered and sent to storage.



Kerosene Merox

Kerosene after a caustic pre wash goes to the Merox reactor consists of a catalyst bed of

activated charcoal impregnated with Merox catalyst. Air is injected with the feed to the Merox

reactor.

Diesel Hydro De-Sulphurisation

Sulfur in Diesel enhances the pollution & contributes significantly to SOx in exhaust emissions.

It leads to corrosion and wear of engine systems.

In order to make eco-friendly diesel, it is desirable to remove impurities by treating the Diesel

streams at certain operating conditions in presence of catalyst and H2 through a process known as

DHDS. Straight run/Cracked diesel streams have certain inherent impurities viz Sulphur,

Oxygen, Olefins, metals etc. Quantity of these impurities depend on crude quality, generally

poorer the crude quality, higher the impurities.

With the implementation of Bharat Stage-II and Euro-III spec, it is mandatory to produce Diesel

with ultra low Sulphur content.

The Process Steps in this unit are:

Feed (Naphtha) Pre-desulphurization

Final desulphurization

Steam Naphtha Reforming

CO HT shift conversion

Final purification of H 2 (PSA)

To remove Sulphur from Naphtha, which is poison to reformer catalyst Naphtha and recycle H2

are heated and sent to Reactor where Sulphur compounds are converted to H2S over Cobalt-

Molybdenum based catalyst.

R-SH + H2 → R-H + H2S



Sulphur reduction from 1000ppm to 10ppm. To reduce the sulphur content of Naphtha from 10

ppm to < 0.5 ppm., Naphtha and H2 are heated and processed in Reactor-II to convert S

compounds to H2S over Cobalt-Molybdenum based catalyst. The H2S removed from the

Reactor-II is absorbed in ZnO reactor.

ZnO + H2S → ZnS + H2O

De-Sulphurised Naphtha is mixed with steam and passed through a Nickel catalyst packed in

vertical narrow 108 tubes mounted in the reformer at high temperature

CnHm + nH2O → nCO + (2n+m)/2H2

CH4 + H2O → CO + 3H2 (endothermic)

C + H2O → CO + H2 (endothermic)

Shift: CO + H2O → CO2 + H2 (exothermic)

Process is endothermic and heat is supplied by fuel firing with 40 top-fired burners.

2.3 Power And Utilities:

Captive Power Plant (CPP)

Capacitive power plant meets the total power demand of the HPCL. This unit comprises for four

gas turbine generators (GTG), two with 9mw capacity (FRAME-3 Machines) each and two with

25mw capacity (FRAME-5 Machines) each.FRAME-3 Machine is a two shaft machine whereas

FRAME-5 Machine is a single shaft machine. HSD and Naphtha are used for the combustion of

gas turbine.

.Steam Generation Unit Steam Generation unit is sub divided in to two i.e. Power plant I& II. In these units the DM

water is converted in to steam by combusting the fuel oil in the presence of air in the boilers CO

produced in FCCU is brought in to CO2 for pollution in power plant II. The steam produced here

is utilized for unit purposes. It is Kg/cm2.



Demineralization water unit

De-Mineralization is a process of removing mineral salts from water by using ion exchange

process. In this unit the raw water is treated & the PH value is maintained at 7 by making the free

from acids, bases, etc, and making it a neutral solution, to use in boilers.

2.4 Environment Related Plant

Effluent treatment plantThe waste water from every plant containing oil is separated and then reused. The remaining

water containing contaminants is neutralized and sent to the sea to control the environmental

pollution.

Sulphur Recovery Unit (SRU):

Sulphur Recovery Unit is designed to process and remove Hydrogen Sulphide (H2S) gas from

fuel gas (3386 - 8838) Nm3/hr, Sour water Stripper gas (38 -257) Nm3/hr and Amine Acid Gas

(1.6 - 26) Nm3/hr, the process is based on the modified Claus reaction.

H2S + 1/2 O2 → H2O + S

This reaction is accomplished by a solution called LO-CAT solution supplied by M/S ARI

Technologies Inc., USA.

All the three gas streams mentioned above are treated with LO-CAT solution. Due to wide

variation in the qualities the fuel gas is treated separately in an absorber column and the other

two streams are treated combined in the absorber section of the oxidizer vessel. In oxidizer

vessel, the spent LO-CAT solution is regeneration using air.



The sulphur generated due to the above reaction remains finely suspended in the LO-CAT

solution. A slipstream form the oxidizer is routed to the sulphur removal system consisting of

mainly a vacuum belt filter, Sulphur Smelter and a molten sulphur storage tank. After removing

sulphur the balance LO-CAT solution routed back to the oxidizer. The treated fuel gas is then

routed to the Refinery Fuel Gas Header. The vent gases forms the oxidizers (free of H2S) are

then vented through a stack.



3. STUDY OF ANALYZERS

The analyzers are mainly used as continuous ambient air monitoring systems

(CAAMS).This gives the analysis of various components in the air that are released

into the atmosphere during the crude extraction process.

For this purpose the software named “ENVIDAS”.This gives the concentration of

various components present in the atmosphere in the stipulated time.The time can be

set from 1 minute to 48 hours.

This CAAMS is used in getting the dust concentration in the plant.In total there are

three monitoring stations in and around the plant.This helps for knowing the amount

of NOx gases, SO2, hydrocarbons, co and co2 present in the pollutant air.

The information will be sent to the APPCS: Andhra Pradesh Pollution Control

Station.The APPCS gives the standards of all the gases to be present in the air.

According to the information obtained, the board will take the action on the

production from the plant.The CAAMS also measures the dust concentration in the

plant.

There are two channels for the measurement of suspended particle matter

1. SPM :Suspended Particle Matter

2. RSPM :Respirable Suspended Particle Matter

This SPM measures the dust particles up to 10ug.The RSPM measures particular matter

up to 25ug.

The HPCL plant uses BAM 1020 model for this purpose.

As per the time the software uploads the data and sends to the central monitoring station

and that will be forwarded to APPCS.



3.1 BAM 1020 :

The main features of this BAM 1020 are

Low operating costs.

Automatic hourly span checks.

It can store upto 182 days of digital data in the internal storage.

Fast and easy audits using common tools.

Highly accurate, reliable and mechanically simple flow system.

Hourly filters advances minimize effects on volatile compounds..

Rugged anodized aluminum, stainless steel and baked enamel construction.

Data retrieval through RS232 ports using direct connection to pc, modem or digital data

collection systems.

PRINCIPLE :

The BAM1020 automatically collects, measures, records the air bourne particulates (in milligram

or micrograms per cubic meter) using the principle of beta ray attenuation.

Thousands of BAM 1020 are deployed all over the world now making it the most successful air

monitoring platforms in the world.

OPERATION:

Each hour, a small 14C (carbon-14) element emits a constant source of high-energy

electrons (known as beta rays) through a spot of clean filter tape.

These beta rays are detected and counted by a sensitive scintillation detector to

determine a zero reading.



The BAM-1020 automatically advances this spot of tape to the sample nozzle, where a

vacuum pump then pulls a measured and controlled amount of dust-laden air through the

filter tape, loading it with ambient dust.

At the end of the hour this dirty spot is placed back between the beta source and the

detector thereby causing an attenuation of the beta ray signal which is used to determine

the mass of the particulate matter on the filter tape and the volumetric concentration of

particulate matter in ambient air.

These are used in measuring the amount of NOX, SO2, CO, HC that are present in the

atmosphere.

These levels are sent to the central board and from it to the A.P. pollution board.


Fig 3.1 BAM-1020 Analyzer Instrument


This is the view of the BAM 1020.recorder,which shows the readings at that particular time.this

is interfaced with the atmosphere, and the readings are plotted down with the help of a recorder

which is as shown below.


Fig 3.2 Analyzer section in HPCL

Fig 3.3 Filter tapes inside BAM-1020


Along with SPM and RSPM there are some gas analyzers like

1. NOX : Chemilumenescene analyzer

2. SO2 : Fluorescence analyzers

3. HC : Hydrocarbon analyzers

4. CO : Gas filter correlation analyzers

Also we find zero span analyzers, weather monitoring station, noise meter

The principles of each analyzer is

a) SPM and RSPM : loss of beta rays

b) NOx :loss of energy due to excitation

c) SO2 :loss of energy where UV rays act as a source

d) CO :M-R ratio

3.2 NOX ANALYSER: (RANGE BETWEEN (0-500ppm))

For the measurement of nitric oxides in the polluted air.

The principle of chemilumenescene is employed.

It means that emission of light during a chemical reaction that does not produce

significant quantities of heat.

The NOx reacts with the ozone, gets excited and return to low energy level with loss of

energy.

The change in the intensity of light energy gives the measurement of NOx

In this process a beta rays are emitted on to the air that is collected and the output of it is passed

through ozone layer.

The NOx present in the atmosphere reacts with the ozone and gets excited to the higher level.

After a certain amount of time this excited NOx gets back to the normal level.

The change in the intensity of light energy gives us the exact measurement of NOx present in the

atmosphere.



3.3 SO2 ANLYSER: (RANGE BETWEEN (0-250ppm))

For the measurement of SO2 in the ambient air.

The principle is fluorescence.

Same as that of NOx, here the UV rays are used for the light radiation.

Even this follows the same process but instead of beta rays the UV rays are used in this process.

Followed by ozone layer. Due to the UV rays the SOx molecules in the air gets activated and

when passed through ozone get excited to higher energy levels. After some time they come back

to the original state.

The difference in the energy levels gives us the measurement of SOx present in the air.

3.4 HC ANALYSER: (RANGE BETWEEN (0-10ppm))

In this, for the measurement of HC, a continuous air supply is required.

Fuel is H2 and carrier gas is N2.

The principle is flame ionization detection.

The number of ions that pass through the flame and the output is a measure of

concentrated HC.

3.5CO ANALYSER: (RANGE BETWEEN (0-10ppm)) This consists of a wheel where in one half is filled with N2 and the other half is filled with

CO+N2.

When the beta rays is passed then N2 does not absorb the radiation where as the other half

having CO and N2, absorbs the light radiation due to the presence of CO.

Then the beta rays are imposed on the optical mirrors in order to adjust the intensity with

that of detectors.

Here the concentration is measured with the reference known as MR ratio which is

approximately 1.2.



3.6 ZERO SPAN CALIBRATION:

This is used for calibrating the analyzers where for the zero.

Zero air modules are used in which the concentration of impurities is almost negligible.

Span measurement is taken by passing the air with maximum amount of impurities in it.

The calibration is done for every one month.



4.PROGRAMMABLE LOGIC CONTROLLER

A Programmable Logic Controller, or PLC for short, is simply a special computer device

used for industrial control systems. It is a sequence controller, i.e it accepts inputs from switches

and sensors, evaluates these in accordance with a stored program, and generates outputs to

control machines and processes.

They are used in many industries such as oil refineries, manufacturing lines, conveyor

systems and so on. Where ever there is a need to control devices the PLC provides a flexible way

to "softwire" the components together.

It uses a programmable memory to store instructions and execute specific functions that

include ON/OFF control, timing, counting, sequencing, arithmetic, and data handling.

4.1 History

The early history of the PLC is fascinating. Imagine if you will a fifty foot long cabinet

filled with relays whose function in life is to control a machine. Wires run in and out of the

system as the relays click and clack to the logic.

Now imagine there is a problem or a small design change and you have to figure it all out on

paper and then shut down the machine, move some wires, add some relays, debug and do it all

over again.

Imagine the labor involved in the simplest of changes. This is the problem that faced the

engineers at the Hydra-matic division of GM motors in the late 1960's. Fortunately for them the

prospect of computer control was rapidly becoming a reality for large corporations as

themselves. So in 1968 the GM engineers developed design criteria for a "standard machine

controller". This early model simply had to replace relays but it also had to be:

A solid-state system that was flexible like a computer but priced competitively with a like

kind relay logic system.


http://www.plcdev.com/glossary/1#term1

http://www.cs.pdx.edu/~harry/Relay/index.html

http://www.cs.pdx.edu/~harry/Relay/index.html


Easily maintained and programmed in line with the all ready accepted relay ladder logic

way of doing things.

Work in an industrial environment with all the dirt, moisture, electromagnetism and

vibration.

Modular in form to allow easy exchange of components and expandability.

This was a tall order in 1968 but four companies took on the challenge.

1. Information Instruments, Inc. (fully owned by Allen-Bradley a year later).

2. Digital Equipment Corp. (DEC)

3. Century Detroit

4. Bedford Associates

Bedford Associates won the contract and quickly formed a new company around the technology

called MODICON after Modular Digital Control. By June of 1969 they were selling the first

viable Programmable Controller, the "084" which sold over one thousand units. These early

experiences gave birth to their next model the "184" in 1973 which set Modicon as the early

leader in programmable controllers. Not to be outdone, the powerhouse Allen-Bradley (all ready

known for its rheostats, relays and motor controls) purchased Information Instruments in 1969

and began development on this new technology.

The early models (PDQ-II and PMC) were deemed to be too large and complex. By 1971 Odo

Struger and Ernst Dummermuth had begun to develop a new concept known as the Bulletin 1774

PLC which would make them successful for years to come. Allen-Bradley termed their new

device the "Programmable Logic Controller" (patent #3,942,158) over the then accepted term

"Programmable Controller". The PLC terminology became the industry standard especially

when PC became associated with personal.

A PLC System

The basic units have a CPU (a computer processor) that is dedicated to run one program that

monitors a series of different inputs and logically manipulates the outputs for the desired



control. They are meant to be very flexible in how they can be programmed while also providing

the advantages of high reliability (no program crashes or mechanical failures), compact and

economical over traditional control systems.

Unlike a personal computer, though the PLC is designed to survive in a rugged industrial

atmosphere and to be very flexible in how it interfaces with inputs and outputs to the real world.

PLCs come in many shapes and sizes. They can be so small as to fit in a shirt pocket while more

involved controls systems require large PLC racks. Smaller PLCs (a.k.a. “bricks”) are typically

designed with fixed I/O points. The PLC’s used at HPCL are the ‘modular’ ones. It’s called

“modular” because the rack can accept many different types of I/O modules that simply slide

into the rack and plug in.

The components that make a PLC work can be divided into three core areas.

The power supply and rack

The central processing unit (CPU)

The input/output (I/O) section


Fig 4.1 A Basic PLC system




Power Supply and Racks:

The rack is the component that holds everything together. Depending on the needs of the control

system it can be ordered in different sizes to hold more modules. Like a human spine the rack

has a backplane at the rear which allows the cards to communicate with the CPU.

The power supply plugs into the rack as well and supplies a regulated DC power to other

modules that plug into the rack. The most popular power supplies work with 120 VAC or 24

VDC sources.

The CPU:


Fig 4.2 PLC Architecture



The brain of the whole PLC is the CPU module. This module typically lives in the slot beside

the power supply. Manufacturers offer different types of CPUs based on the complexity needed

for the system.

The CPU consists of a microprocessor, memory chip and other integrated circuits to control

logic, monitoring and communications.

The CPU has different operating modes. In programming mode it accepts the downloaded logic

from a PC. The CPU is then placed in run mode so that it can execute the program and operate

the process.

Since a PLC is a dedicated controller, it will only process this one program over and over again.

One cycle through the program is called a scan time and involves reading the inputs from the

other modules, executing the logic based on these inputs and then updated the outputs

accordingly.

The scan time happens very quickly (in the range of 1/1000th of a second). The memory in the

CPU stores the program while also holding the status of the I/O and providing a means to store

values.

I/O System:

The I/O system provides the physical connection between the equipment and the PLC. Opening

the doors on an I/O card reveals a terminal strip where the devices connect. There are many

different kinds of I/O cards which serve to condition the type of input or output so the CPU can

use it for its logic.

It's simply a matter of determining what inputs and outputs are needed, filling the rack with the

appropriate cards and then addressing them correctly in the CPUs program.

Input Module: These modules act as interface between real-time status of process variable

and the CPU.



Analog input module: Typical input to these modules is 4-20 mA, 0-10 V. For eg: Pressure,

Flow, Level Tx, RTD (Ohm), Thermocouple (mV)

Digital input module : Typical input to these modules is 24 V DC, 115 V AC and 230 V AC.

For eg: Switches, Pushbuttons, Relays, pump valve on off status.

Output Module: These modules act as link between the CPU and the output devices in the

field.

Analog output module : Typical output from these modules is 4-20 mA, 0-10V. For eg: Control

Valve, Speed, and Vibration

Digital output module: Typical output from these modules is 24 V DC, 115 V AC and 230 V

AC. For eg: Solenoid Valves, lamps, Actuators, dampers, Pump valve on off control.

PLC and PC are said to be similar in their physical construction but differ in their functions.

A PLC is specifically designed for harsh conditions with electrical noise, magnetic fields,

vibration, extreme temperatures or humidity. Common PCs are not designed for harsh

environments. Industrial PCs are available but cost more.

By design PLCs are friendlier to technicians since they are in ladder logic and have easy

connections. Operating systems like Windows are common. Connecting I/O to the PC is not

always as easy.



.

PLCs execute a single program in sequential order. They have better ability to handle events in

real time. PCs, by design, are meant to handle simultaneous tasks. They have difficulty handling

real time events.

4.2 Vendors of PLCs used in HPCL:1. ICS Triplex

2. Schneider Electric

3. Honeywell Authority India Limited (HAIL)

4. Modicon

5. GE FanucPage | 30

DEPARTMENT OF ECE, GITAM UNIVERISTY

Fig 4.3 A PLC System


Various PLCs used in Visakh Refinery:

S No PLC

SYSTEM

MODEL

LOCATIO

N UNITS BACKUP CONTENTS

1

SCHNEIDE

R QUANTUM CENTUM

OLD CO

BLR LADDER LOGIC

2

ALLEN

BRADLEY 2/5 CPP CPP HRSG1 SUPPLM FIRING

3

ALLEN

BRADLEY 2/5 CPP CPP HRSG2 SUPPLM FIRING

4

ALLEN

BRADLEY 5/20 PP1 F/R PP1 WIL8 LADDER LOGIC

5

ALLEN

BRADLEY 5/40 CENTUM CDU3

42F01/F02/46F01 LADDER

LOGIC

6

ALLEN

BRADLEY 5/60 LPG C/R LPG LPG LOGIC WITH MMI

7

ALLEN

BRADLEY SLC CDU-I CDU-I

2F04 SOOT BLOWERS

LADDER

8

ALLEN

BRADLEY SLC CENTUM DHDS-SRU 65K201A LADDER LOGIC

9

ALLEN

BRADLEY SLC CENTUM DHDS-SRU 65K201B LADDER LOGIC

10

ALLEN

BRADLEY SLC CENTUM DHDS-SRU 65K101B LADDER LOGIC

11

ALLEN

BRADLEY SLC CENTUM DHDS-SRU 65K101A LADDER LOGIC

12

ALLEN

BRADLEY SLC PP1 F/R PP1

STACK ANALYSERS

LADDER

13

ANSHUMA

N DMP DMP SILICA ANAL LADDER

14 GE-FANUC LM 90/30 CENTUM PP1 NCO BOILER LADDER



15 GE-FANUC LM 90/30 DMP C/R DMP2 DM2 LOGIC WITH HMI

16 GE-FANUC LM 90/30 DMP C/R DMP3 DM3 LOGIC WITH HMI

17 GE-FANUC LM 90/30 F&S BLDG F & S FIRE SIREN SYSTEM

18

ICS-

TRIPLEX

REGENT

PLUS+ CENTUM FCCU1(R)

MAB / CAB LADDER

LOGIC

19 MARK-V TMR CPP C/R CPP I-Station T1/T2 Backup

20 MARK-V TMR CPP C/R CPP I-Station T3 Backup

21 MARK-V TMR CPP C/R CPP I-Station T4 Backup

22 MODICON MICRO CPP CPP ANALYSERS LADDER

23 MODICON

TXS

QUANTUM CENTUM H2

PSA CONTROLS WITH

MMI

24 SIEMENS MICRO ETP2 F & S FIRE WATER SYSTEM

25 SIEMENS S5 CENTUM CDU2

11F01 SOOT BLOWERS

LADDER

26 SIEMENS S5-SIMATIC PP1 F/R PP1 BHPV BOILER LADDER

2

7 SIEMENS S7 FCCU1 FCCU1 CAT TIMER LADDER

28 THL 620-12 PP2 F/R WIL B BLR LADDER LOGIC

29 THL 620-16 CPP CPP HRSG3 S/B LADDER

30 THL 620-16 CPP CPP HRSG4 S/B LADDER

31 THL 620-35 CPP CPP HRSG4 SUPPLM FIRING

32 THL 620-35 CPP CPP HRSG3 SUPPLM FIRING

33 THL 620-35 CDU1 F/R 2F01/F02 LADDER LOGIC

34 THL 620-35 CENTUM

FCCU1(R)

WGC LADDER LOGIC

35 THL 620-35

FCCU2

FIELD FCCU2 MAB LADDER LOGIC

36 THL 620-35

FCCU2

FIELD FCCU2 WGC LADDER LOGIC

37 THL 620-35 CENTUM 2F04 LADDER LOGIC



WITH LMM

38 THL

620-35

WITH LMM CENTUM

FCCU1(R)

RR LADDER LOGIC

39 THL FSC CENTUM D-SRU FSC BACK UP

40 THL FSC CENTUM DHDS FSC BACK UP

41 THL FSC CENTUM H2 FSC BACK UP

42 THL FSC SOE CENTUM DHDS COFIGURATION BACKUP

43 THL

SMOKE

DET

SYSTEM F&S BLDG F&S

DEVELOPEMENT PC

BACKUP

4.3 Configuration of PLCs ALLEN BRADLEY PLC:

MODICON PLC:


Fig 4.4 Allen Bradley PLC

Fig 4.5 Modicon PLC

Table-4 List of Various PLCs used in Visakh refinary


SIEMENS PLC:

4.4 Applications of PLCs


Fig 4.6 Siemens PLC

Fig 4.5 Modicon PLC


PLCs are used in industries where there is a need for the scan time to be the minimum possible.

For emergency shutdown of furnaces, heaters, batch processing, motor valves, plant interlocks,

machine protection system, ESG of any furnaces, turbine control system, water treatment in de-

mineralized plants, fire water auto cutting systems, fire siren operation systems, etc.

Traditional application of PLCs:

Packaging

Bottling and canning

Material Handling

Power Generation

HVAC/Building control systems

Security Systems

Automated Assembly

Water Treatment

Food and Beverage

Chemicals

Pulp and Paper

Pharmaceuticals

Metals

In industry, there are many production tasks, which are of highly repetitive nature. Although

repetitive and monotonous, each stage needs careful attention of operator to ensure good

quality of final product.

Many a times, flow supervision of process causes high fatigue on operator, resulting in loss

of track of process control.

Sometimes, it is hazardous also as in case of potentially explosive chemical processes.

Under all the above conditions we can use PLCs effectively in totally eliminating the

possibilities of human error.



Some of the capabilities of PLCs are:

Logic control

PID control

Co-ordination and communication

Operator control

Signaling and listing etc.

4.5 Advantages of PLCs

Reduced space:

PLCs are fully solid state and hence extremely compact as compared to hardwired controller

wherein electromechanical devices are used.

Energy saving:

Average power consumption is just one tenth of power consumed by an equivalent relay logic

control.

Ease of Maintenance:

Modular replacement

Easy troubleshooting

Error diagnostics with programmer

Economical:

Considering one time investment PLC is most economical system

Cost of PLC recovers within a short period (low payback period)

Greater Life and Reliability:



Static devices, hence lesser number of moving parts, reduces wear and tear In the case of

hardwired logic the control, hardware is either electromechanical or pneumatic and therefore it is

prone to faults due to wear and tear of moving parts resulting in lesser ON TIME of the system.

Tremendous flexibility:

To implement changes in control logic, no rewiring is required. So, considerable time is

saved.

PLC can carry out complex functions such as generation of time delays, counting,

comparing, arithmetic operations etc.

Online as well as Offline programming is possible.

High processing speed and greater flexibility in processing in both analog and digital

signals.

Suitability for closed loop tasks with several loops and high sampling frequencies.

Shorter Project Time:

The hardwired control system can be constructed only after the task is defined. In PLC, however,

the construction of the controller and wiring are independent of control program definition. This

means that the total hardware is standard and desired control is achieved through program.

Easier Storage Archiving and Documentation:

This is due to its compatibility with PC/AT, Printer and Floppy Disk etc.



5.DISTRIBUTED CONTROL SYSTEM

Distributed Control System is a type of automated control system that is distributed throughout a

machine to provide instructions to different parts of the machine. Instead of having a centrally

located device controlling all machines, each section of a machine has its own computer that

controls the operation.

For instance, there may be one machine with a section that controls dry elements of cake frosting

and another section controlling the liquid elements, but each section is individually managed by

a DCS. A DCS is commonly used in manufacturing equipment and utilizes input and output

protocols to control the machine.

5.1 History

Early minicomputers were used in the control of industrial processes since the beginning of the

1960s. The IBM 1800, for example, was an early computer that had input/output hardware to

gather process signals in a plant for conversion from field contact levels (for digital points) and

analog signals to the digital domain.

The DCS was introduced in 1975. Both Honeywell and Japanese electrical engineering firm

Yokogawa introduced their own independently produced DCSs at roughly the same time, with

the TDC 2000 and CENTUM systems, respectively. US-based Bristol also introduced their UCS

3000 universal controller in 1975. In 1980, Bailey (now part of ABB) introduced the

NETWORK 90 system. Also in 1980, Fischer & Porter Company (now also part of ABB)

introduced DCI-4000 (DCI stands for Distributed Control Instrumentation).

The DCS largely came about due to the increased availability of microcomputers and the

proliferation of microprocessors in the world of process control. Computers had already been



applied to process automation for some time in the form of both Direct Digital Control (DDC)

and Set Point Control. In the early 1970s Taylor Instrument Company, (now part of ABB)

developed the 1010 system, Foxboro the FOX1 system and Bailey Controls the 1055 systems.

All of these were DDC applications implemented within mini-computers (DEC PDP 11, Varian

Data Machines, MODCOMP etc) and connected to proprietary Input/output hardware.

Sophisticated (for the time) continuous as well as batch control was implemented in this way.

A more conservative approach was Set Point Control, where process computers supervised

clusters of analog process controllers. A CRT-based workstation provided visibility into the

process using text and crude character graphics. Availability of a fully functional graphical user

interface was a way away.

5.2 The Hierarchy of DCS

Dedicated control system

Centralized computer control

Distributed control system

Dedicated control system:

As the name suggests, a computer is assigned to each process. However, this makes the system

bulky and costly. As there are a greater number of systems, there may be lack of coordination.


Fig 5.1 Dedicated control system


Centralized computer control :

This system uses a computer called Mainframe computer. There is said to be only one single

computer in the system, controlling all the functions.

The main disadvantage of this system is that as a single computer has to control the system, it is

costly. If there is a problem with any one loop, the total system gets smashed and identifying the

loop is also very difficult. As it needs to handle many processes, the speed decreases.

Programming is very difficult. The system is not reliable and accurate.

About fifty years back pneumatic system was used for process controls. The transmitters and

controllers were all pneumatic instruments operating on 3 to 15 psi air signals. The main

disadvantages of these pneumatic instruments were

Very slow, response

Highly maintenance oriented

Specialized skill required for maintenance


Fig 5.2 Centralized Control Network


Developments in the electronic field in 1970s led to the use of electronic instruments. Electronic

transmitters and electronic controllers came to be widely used in process control applications.

They were all analog instruments and 4 to 20 ma became the industry standard for

instrumentation signals. Towards 1980 remarkable progress was made in digital electronics.

The advent of microprocessor initiated a new era in the field of instrumentation for process

control. The existing process plant pneumatic and electronics instrumentation is getting replaced

with the microprocessor based distributed control system.

New plants are coming up only with the distributed digital control system (DCS). The benefits

that accrue from the introduction of the DCS in then old plants as well as a new plants are many

such as improved productivity, high amount of flexibility, advanced control and optimization,

quick start up of the plant, less maintenance on the instrumentation, MIS, etc.

Following is a brief description of the various components of the system.

5.3 Distributed Control Systems in HPCL

The basic functionality of the DCS is “The work is distributed depending upon the

functionality.” The DCS is said to have a layered structure.

Each layer corresponds to a group of group of functions to be performed on lower layer, on

getting some instructions from the higher layer and each layer can work independently.

Three companies provide HPCL with DCS. They are:

1. Honeywell Automation India Limited (HAIL)

2. Yokogawa India Limited (YIL)

3. Asian Brown Bravery (ABB)

At the HPCL Visakh Refinery,

The CDU-I, FCCU-I, DHDS and SRU are operated by using the Honeywell DCS. Page | 41



The Power plants, CDU-II, FCCU-II, MEROX, SRU & PRU units are operated by using

the Yokogawa DCS.

The CDU-III and Oil Movement and Storage units are operated using ABB DCS.

6.DATA COMMUNICATION

6.1 SERIAL COMMUNICATION

In telecommunication and computer science, serial communication is the process of sending data

one bit at one time, sequentially, over a communication channel or computer bus.

This is in contrast to parallel communication, where several bits are sent together, on a link with

several parallel channels. Serial communication is used for all long-haul communication and

most computer networks, where the cost of cable and synchronization difficulties make parallel

communication impractical.

At shorter distances, serial computer buses are becoming more common because of a tipping

point where the disadvantages of parallel buses (clock skew, interconnect density) outweigh their

advantage of simplicity (no need for serializer and deserializer (SERDES))

Improved technology to ensure signal integrity and to transmit and receive at a sufficiently high

speed per lane have made serial links competitive. The migration from PCI to PCI Express is an

example.

Different Serial Communication Architectures:

RS 232

RS 422



RS 485

Ethernet

ModBus

RS 232

Definitely the most popular interface, also being one of the first. However, things may soon

change for obvious reasons. Any PC that is purchased will have one (and sometimes more) RS-

232 port.

Sometimes, they are simply referred to as SERIAL PORTS, however this may cause confusion

since there are other Serial interfaces available. RS-232 is widely used because it is so readily

available. You don't usually need to purchase an RS-232 port since it is available on any PC.

However, it does have some disadvantages. Here are a few:

Limited Distance - Cable lengths are limited to 50 ft or less. Many will claim to

go further, but this is not recommended, and is not part of the RS-232 specification.

Susceptible to Noise - RS-232 is single-ended, which means that the transmit and

receive lines are referenced to a common ground

Not Multi-drop - You can only connect one RS-232 device per port. There are

some devices designed to echo a command to a second unit of the same family of

products, but this is very rare. This means that if you have 3 meters to connect to a PC,

you will need 3 ports, or at least, an RS-232 multiplexor.

RS-485

RS-485 is very similar to RS-422. So much so that it often causes confusion. Both are multi-

drop, and both can communicate via very long distances, so then why choose one over the other?



First of all, RS-485 is generally a 2-wire system, although some manufacturers may specify 4-

wire RS-485, which is far less common and very similar to RS-422.

It is important that you identify which one is being employed when considering an instrument.

Here are some main differences between 2-wire RS-485 and RS-422:

RS-485 can have multiple Commanding Devices and multiple Listening Devices.

RS-422 can have only one Commander and multiple Listeners. For example, you can

connect one PC (the Commanding device) to 10 temperature controllers (listeners).

The PC can instruct any of the controllers to change setpoint, or to send a

temperature reading, but none of the controllers can command any of the other

controllers. With RS-485, you can have multiple PC's and multiple controllers on one

bus, so that one PC can send a command to change a setpoint,and another PC can send a

command to send back data, etc. Remember that all devices on the bus must have a

unique unit address, so that only the addressed unit will respond. (similar to RS-422)

RS-485 wiring is easier since you are only dealing with 2 wires instead of 4.

Programming RS-485 is more difficult, since you are sending and receiving on

the same two wires, you need to enable and disable the transmitter at the correct time so

that you may perform proper communications. Imagine sending a command $2SEND out

of the transmitter. If the transmitter is not turned off in time, then data being sent by

another device will be missed. If the transmitter is turned off too quickly, there is a

chance that part of the command $S2END will be truncated before it ever has a chance

finishing the transmission of the character bits.

When programming an RS-485 plug-in card, you would read the STATUS

REGISTER to determine if it is time to switch or not. Some cards, such as the OMG-

ULTRA-485 has an AUTO mode where it is intelligent enough to do this automatically,

making it transparent to the programmer. Since RS-422, and RS-232 for that matter, have

separate transmit and receive lines, they are easier to implement. Of course, there are Page | 44



other matters to consider such as handshaking, but will not be covered in this brief

description.

6.2 PARLLEL COMMUNICATION:

In telecommunication and computer science, parallel communication is a method of sending

several data signals simultaneously over several parallel channels. It contrasts with serial

communication; this distinction is one way of characterizing a communications link.

The basic difference between a parallel and a serial communication channel is the number of

distinct wires or strands at the physical layer used for simultaneous transmission from a device.

Parallel communication implies more than one such wire/strand, in addition to a ground

connection. An 8-bit parallel channel transmits eight bits (or a byte) simultaneously. A serial

channel would transmit those bits one at a time. If both operated at the same clock speed, the

parallel channel would be eight times faster.

A parallel channel will generally have additional control signals such as a clock, to indicate that

the data is valid, and possibly other signals for handshaking and directional control of data

transmission.

Examples of parallel communication systems

Computer peripheral buses: ISA, ATA, SCSI, PCI and Front side bus, and the once-

ubiquitous IEEE-1284 / Centronics "printer port"

Laboratory Instrumentation bus IEEE-488

Comparison of Serial and Parallel Communication

Before the development of high-speed serial technologies, the choice of parallel links over serial

links was driven by these factors:

Speed: Superficially, the speed of a parallel data link is equal to the number of bits sent

at one time times the bit rate of each individual path; doubling the number of bits sent at Page | 45



once doubles the data rate (see Parallel transmission). In practice, skew reduces the speed

of every link to the slowest of all of the links.

Cable length: Crosstalk creates interference between the parallel lines, and the effect

worsens with the length of the communication link. This places an upper limit on the

length of a parallel data connection that is usually shorter than a serial connection.

Complexity: Parallel data links are easily implemented in hardware, making them a

logical choice. Creating a parallel port in a computer system is relatively simple,

requiring only a latch to copy data onto a data bus.

In contrast, most serial communication must first be converted back into parallel form by

a universal asynchronous receiver/transmitter (UART) before they may be directly

connected to a data bus.

The decreasing cost of integrated circuits, combined with greater consumer demand for speed

and cable length, has led to parallel communication links becoming deprecated in favor of serial

links; for example, IEEE 1284 printer ports vs. USB, Advanced Technology Attachment vs.

Serial ATA, and SCSI vs. FireWire.

On the other hand, there has been a resurgence of parallel data links in RF communication.

Rather than transmitting one bit at a time (as in Morse code and BPSK), well-known techniques

such as PSM, PAM, and Multiple-input multiple-output communication send a few bits in

parallel. (Each such group of bits is called a "symbol").

Such techniques can be extended to send an entire byte at once (256-QAM). More recently

techniques such as OFDM have been used in Asymmetric Digital Subscriber Line to transmit

over 224 bits in parallel, and in DVB-T to transmit over 6048 bits in parallel.



6.3 Fiber Optic Communication:

Fiber-optic communication is a method of transmitting information from one place to another by

sending pulses of light through an optical fiber. The light forms an electromagnetic carrier wave

that is modulated to carry information.

First developed in the 1970s, fiber-optic communication systems have revolutionized the

telecommunications industry and have played a major role in the advent of the Information Age.

Because of its advantages over electrical transmission, optical fibers have largely replaced

copper wire communications in core networks in the developed world.

The process of communicating using fiber-optics involves the following basic steps: Creating the

optical signal involving the use of a transmitter, relaying the signal along the fiber, ensuring that

the signal does not become too distorted or weak, receiving the optical signal, and converting it

into an electrical signal.

Applications:

Optical fiber is used by many telecommunications companies to transmit telephone signals,

Internet communication, and cable television signals. Due to much lower attenuation and

interference, optical fiber has large advantages over existing copper wire in long-distance and

high-demand applications. However, infrastructure development within cities was relatively

difficult and time-consuming, and fiber-optic systems were complex and expensive to install and

operate. Due to these difficulties, fiber-optic communication systems have primarily been

installed in long-distance applications, where they can be used to their full transmission capacity,

offsetting the increased cost.

Transmitters: The most commonly-used optical transmitters are semiconductor devices such

as light-emitting diodes (LEDs) and laser diodes.



Receivers: The main component of an optical receiver is a photodetector, which converts light

into electricity using the photoelectric effect. The photodetector is typically a semiconductor-

based photodiode.

Fiber: An optical fiber consists of a core, cladding, and a buffer (a protective outer coating), in

which the cladding guides the light along the core by using the method of total internal

reflection.

The core and the cladding (which has a lower-refractive-index) are usually made of high-quality

silica glass, although they can both be made of plastic as well. Connecting two optical fibers is

done by fusion splicing or mechanical splicing and requires special skills and interconnection

technology due to the microscopic precision required to align the fiber cores.

Two main types of optical fiber used in fiber optic communications include multi-mode optical

fibers and single-mode optical fibers. A multi-mode optical fiber has a larger core (≥ 50

micrometres), allowing less precise, cheaper transmitters and receivers to connect to it as well as

cheaper connectors.

However, a multi-mode fiber introduces multimode distortion, which often limits the bandwidth

and length of the link. Furthermore, because of its higher dopant content, multimode fibers are

usually expensive and exhibit higher attenuation.

The core of a single-mode fiber is smaller (<10 micrometres) and requires more expensive

components and interconnection methods, but allows much longer, higher-performance links.

Comparison with Electric Transmission:

The choice between optical fiber and electrical (or copper) transmission for a particular system is

made based on a number of trade-offs. Optical fiber is generally chosen for systems requiring

higher bandwidth or spanning longer distances than electrical cabling can accommodate.

The main benefits of fiber are its exceptionally low loss, allowing long distances between

amplifiers or repeaters; and its inherently high data-carrying capacity, such that thousands of

electrical links would be required to replace a single high bandwidth fiber cable.

Another benefit of fibers is that even when run alongside each other for long distances, fiber

cables experience effectively no crosstalk, in contrast to some types of electrical transmission



lines. Fiber can be installed in areas with high electromagnetic interference (EMI),(along the

sides of utility lines, power-carrying lines, and railroad tracks). All-dielectric cables are also

ideal for areas of high lightning-strike incidence.

For comparison, while single-line, voice-grade copper systems longer than a couple of

kilometers require in-line signal repeaters for satisfactory performance; it is not unusual for

optical systems to go over 100 kilometers (60 miles), with no active or passive processing.

Single-mode fiber cables are commonly available in 12 km lengths, minimizing the number of

splices required over a long cable run. Multi-mode fiber is available in lengths up to 4 km,

although industrial standards only mandate 2 km unbroken runs. In short distance and relatively

low bandwidth applications, electrical transmission is often preferred.

6.4 ETHERNET:

Ethernet is a family of frame-based computer networking technologies for local area networks

(LANs). The name comes from the physical concept of the ether.

It defines a number of wiring and signaling standards for the Physical Layer of the OSI

networking model, through means of network access at the Media Access Control (MAC) /Data

Link Layer, and a common addressing format.

Ethernet is standardized as IEEE 802.3. The combination of the twisted pair versions of Ethernet

for connecting end systems to the network, along with the fiber optic versions for site backbones,

is the most widespread wired LAN technology.

It has been in use from around 1980 to the present, largely replacing competing LAN standards

such as token ring, FDDI, and ARCNET.

Ethernet was originally based on the idea of computers communicating over a shared coaxial

cable acting as a broadcast transmission medium. The methods used show some similarities to

radio systems, although there are fundamental differences, such as the fact that it is much easier

to detect collisions in a cable broadcast system than a radio broadcast.

The common cable providing the communication channel was likened to the ether and it was

from this reference that the name "Ethernet" was derived.



From this early and comparatively simple concept, Ethernet evolved into the complex

networking technology that today underlies most LANs. The coaxial cable was replaced with

point-to-point links connected by Ethernet hubs and/or switches to reduce installation costs,

increase reliability, and enable point-to-point management and troubleshooting

StarLAN was the first step in the evolution of Ethernet from a coaxial cable bus to a hub-

managed, twisted-pair network. The advent of twisted-pair wiring dramatically lowered

installation costs relative to competing technologies, including the older Ethernet technologies.

Above the physical layer, Ethernet stations communicate by sending each other data packets,

blocks of data that are individually sent and delivered. As with other IEEE 802 LANs, each

Ethernet station is given a single 48-bit MAC address, which is used to specify both the

destination and the source of each data packet.

Network interface cards (NICs) or chips normally do not accept packets addressed to other

Ethernet stations. Adapters generally come programmed with a globally unique address, but this

can be overridden, either to avoid an address change when an adapter is replaced, or to use

locally administered addresses.

Due to the ubiquity of Ethernet, the ever-decreasing cost of the hardware needed to support it,

and the reduced panel space needed by twisted pair Ethernet, most manufacturers now build the

functionality of an Ethernet card directly into PC motherboards, eliminating the need for

installation of a separate network card.

6.5 MODBUS:

Modbus is a serial communications protocol published by Modicon in 1979 for use with its

programmable logic controllers (PLCs). It has become a de facto standard communications

protocol in industry, and is now the most commonly available means of connecting industrial

electronic devices.

At HPCL-VR one of the most crucial uses of the Modbus is that it is used for interconnection

between PLCs and DCS. The main reasons for the extensive use of Modbus over other

communications protocols are:



It is openly published and royalty-free

Relatively easy industrial network to deploy

It moves raw bits or words without placing many restrictions on vendors

Modbus allows for communication between many devices connected to the same network, for

example a system that measures temperature and humidity and communicates the results to a

computer. Modbus is often used to connect a supervisory computer with a remote terminal unit

(RTU) in supervisory control and data acquisition (SCADA) systems.

Protocol Versions:

Versions of the Modbus protocol exist for serial port and for Ethernet and other networks that

support the Internet protocol suite.

Most Modbus devices communicate over a serial EIA-485 physical layer.

For serial connections, two variants exist, with different representations of numerical data and

slightly different protocol details. Modbus RTU is a compact, binary representation of the data.

Modbus ASCII is human readable, and more verbose.

Both of these variants use serial communication. The RTU format follows the commands/data

with a cyclic redundancy check checksum, while the ASCII format uses a longitudinal

redundancy check checksum. Nodes configured for the RTU variant will not communicate with

nodes set for ASCII, and the reverse.

For connections over TCP/IP, the more recent variant Modbus/TCP exists. It does not require a

checksum calculation.

Data model and function calls are identical for all three communication protocols; only the

encapsulation is different.

An extended version, Modbus Plus (Modbus+ or MB+), also exists, but remains proprietary to

Modicon. It requires a dedicated co-processor to handle fast HDLC-like token rotation. It uses

twisted pair at 1 Mbit/s and includes transformer isolation at each node, which makes it Page | 51



transition/edge triggered instead of voltage/level triggered. Special interfaces are required to

connect Modbus Plus to a computer, typically a card made for the ISA (SA85), PCI or PCMCIA

bus.

Implementations:

Almost all implementations have variations from the official standard. Different varieties may

not communicate correctly between different suppliers equipment. Some of the most common

variations are:

Data Types

Floating Point IEEE

32 bit integer

8 bit data

mixed data types

bit fields in integers

multipliers to change data to/from integer. 10, 100, 1000, 256 ...

Protocol extensions

16 bit slave addresses

32 bit data size (1 address = 32 bits of data returned.)

word swapped data

Limitations

Modbus was designed in the late 1970s to communicate to programmable logic

controllers, the number of data types is limited to those understood by PLCs at the time.

Large binary objects are not supported.



No standard way exists for a node to find the description of a data object, for example, to

determine if a register value represents a temperature between 30 and 175 degrees.

Since Modbus is a master/slave protocol, there is no way for a field device to "report by

exception" (except over Ethernet TCP/IP, called open-mbus)- the master node must

routinely poll each field device, and look for changes in the data. This consumes

bandwidth and network time in applications where bandwidth may be expensive, such as

over a low-bit-rate radio link.

Modbus is restricted to addressing 247 devices on one data link, which limits the number

of field devices that may be connected to a master station (once again Ethernet TCP/IP

proving the exception).

Modbus transmissions must be contiguous which limits the types of remote

communications devices to those that can buffer data to avoid gaps in the transmission.



BIOBLIOGRAPHY

1. Computer architecture and Organisation : Morris Mano Mc.Graw-Hill,Newyork, Second edition.

2. Advanced Microprocessors and pheripherals :A.K.Ray ,K M Bhurchandi,Mc.Graw-Hill Second edition.

3. IEEE standard Programmable Logic Interface Technology :The institute of Electrical and Electronics Engineers,1994.

4. BAM-1020 HPCL-VR user maintainance manual 3rd Edition.

5. Wireless Communication And Networks :Theodre Rappaport.Willey Publication

6. Abromovici.M.breuer and Freid Man ,F Data Communication systems and its testing. Indianapolis,Ind.Wiley-IEEE press,1994.


Documents

HPCL Project report