Acknowledgement

Main aim of this practical training is to get practical knowledge about the working of an industry and use of modern engineering in it. Training makes us to know how the knowledge from book is applied to practical life. During my schedule in H.Z.L., Debari, I got an opportunity to know about the working condition in plant and got more knowledge about my branch of study.

Behind completion of this training, some persons played a key role directly or indirectly.

So I would like to thank those persons without whose contribution this work proves too much for me.

I express my deep regards and gratitude to honorable Mr. Pankaj Joshi Head of

Electrical Department for suggesting the advice, keen interest, and constant boost up, invaluable guidance.

I am grateful to “Mr.B.P.Kant” working at HZL, Debari. for giving me guidance,

kind support and mental preparation for training report. I am thankful and grateful to “Mr.P.K.JAIN” Sr.Manager (HRDC) at H.Z.L., Debari

(RAJ.) for giving me chance of training at their prestigious industry, which will be helpful in my progress toward bright future.

I am also helpful to the executive staff, technical and non-technical staff of H.Z.L. for

extending their kind support, information and practical knowledge during my four-week practical training at their unit H.Z.L., Debari, Udaipur.

Preface

Practical training is a way to implement theoretical knowledge to practical use. To become a successful engineer it is necessary to have a sound practical knowledge because it is the only way by which one can acquire proficiency & skill to work successfully in different industries. It is proven fact that bookish knowledge is not sufficient because things are not as ideal in practical field as they should be.

Hindustan Zinc Ltd. is one of the best examples to understand the production process & productivity in particular of Zinc.

It is a matter of great pleasure that our college authorities have recommended a practical training of 30 days to supplement our theoretical knowledge acquired in the college.

This report is an attempt made to study the overall production system & related action of Zinc Smelter, Debari a unit a HZL. It is engaged in the production of high grade Zinc metal & other byproducts viz. Cd, Sulphuric acid etc. since 1968 adopting hydro metallurgical technology.

Contents

1. ABOUT HIDUSTAN ZINC LTD. 1-25

1) Introduction……………………………………………………………………………5

2) Properties of Zinc (metallic) at 293K…………………………….................................8

3) Applications of Zinc…………………………………………………………………...8 4) Safety Department…………………………………………………………………......9 5) Zinc smelting steps in Various plant…………………………………………………..10

5.1) Roaster plant……………………………………………….…………………....105.2) Boiler ckt………………………………………………………………………..145.3) Acid plant……………………………………………………………………….145.4) Leaching & Purification plant…………………………………………………..16

5.5) Residue Treatment plant………………………………………………………...19

5.6) Zinc dust plant…………………………………………………………………..19

5.7) Zinc Electrolysis & Melting……………………………………………………20

5.8) Solution Cooling & Storage…………………………………………………….20

6) Central Workshop……………………………………………………………………..21

7) Instrumentation Department…………………………………………………………..24

2. PROJECT :- STUDY OF PROGRAMMABLE LOGIC CONTROLLERS

1) Introduction ……………………………………………………………………….26

2) Need of PLC ……………………………………………………………………....27

3) Plc past and present…………………………………………………………………28

4) Advantages of PLC…………………………………………....................................30

5) PLC features………………………………………………………………………...31

6) Internal architecture of PLC………………………………………………………...32

7) The PLC system Hardware………………………………………………………….41

8) Principle of Operation ………………………………………………………………43

9) PLCs versus Other Types of Controls……………………………………………….44

10) Programming of PLC…………………………………….. …………………….......45

11) Programmable Logic Controllers (PLCs) Specifications……………………………50

12) Advancements in PLC……………………………………………………………….54

13) Distributed Control System (DCS)…………………………………………………..56

14) Hybrid Systems………………………………………………………………………58

4. CONCLUSION & BIBLIOGRAPHY ……….................................59-60

ABOUT HINDUSTAN ZINC LTD.

1. Introduction:

Hindustan Zinc Limited (HZL):

One of the India’s leading Zinc Producers and exceptional in its extent of this technological

complete with vertical integration IN other non-ferrous metals.

HZL was incorporation on 10th February 1968 as a public sector company after the take

over of the Erstwhile Metal Corporation of India. It was expanded on December 1976 and later on

April 1985. The foundation stone of this company is being kept by Shri Manu Bhai Shah Minister

of Industry on 26 June 1962.

HZL operations are broad lend based & its activities range from exploration, mining & are

processing to smelting and refining of Pb, Zn, Cd, Co, Cu & other precious metals. It also produces

sulphuric acid and rock phosphate.

Total plant area is 200.3 Hectare of HZL, Debari. Total Zinc production of Hindustan Zinc

is 73206Tonnes per Annum and major suppliers of HZL are Finland, Sweden and Germany.

Overview:

Name & Location : Debari Zinc Smelter,

Village Debari ,

Udaipur (Rajasthan)

Age : Feb.1968 (40 years)

Expanded Dec.,1976

April 1985 & Dec.2000

Process : Hydrometallurgy

Covered Area (Ha) : 22.65

Total Plant Area (Ha) : 126

Zinc Smelter Debari is hydrometallurgical smelter producing high grade Zinc metal and other by

products like Cd and Sulphuric Acid since 1968.

1. Operating Capacity:

Zn : 80,000MT

Acid : 130,000MT

Cd : 250MT

Zinc dust : 360MT

2. Work force: 876 Nos.

Managerial & Engineering Staff : 84 Nos

Supervisory & Technical Staff : 58 Nos.

Labour : 729 Nos.

(a) Skilled : 154Nos.

(b) Semi-Skilled : 555Nos.

(c) Unskilled : 250Nos.

3. Raw Material Supplies:-

(a) Zawar Mines

(b) Agucha Mines

(c) Rajpura Dariba Mines

4. Product Buyers:-

(a) Tata

(b) Bhel

(c) Steel Companies

5. Steps of process:-

(6) Maximum Power Demand: - 38-40MW

(7) Process Collaborators:-

1. Krebs Penorrova, France:-

Leaching, Purification, Electrolysis

2. Lurgi, GMBH, and Germany:-

Mining

Roasting

Leaching

Electrolysis

Melting

Zinc Ingots

Roaster and gas clearing

3. Auto Kumpu, Finland:-

RTP, Wartsila Plant

4. I.S.C., ALLOY, U.K.:-

Zinc dust plant, Allen Power Plant

2. Properties of Zinc (metallic) at 293K

1. Density : 7140Kg./m3

2. Melting Point : 693K

3. Specific Latent Heat of Fusion : 10 J/ Kg

4. Specific heat capacity : 385 J/Kg/K

5. Linear expansivity : 31/K

6. Thermal conductivity : 111 W/m/k

7. Electric Sensitivity : 5.9 ohm –meter

8. Temp. Coefficient of resistance : 40/k

9. Tensile Strength : 150 Mpa

10. Elongation : 50%

11. Young’ modulus : 110 Gpa

12. Passion’s Ratio : 0.25

3. Applications of Zinc:

Galvanizing: It is one of the best forms of protection against corrosion, used extensively in

building, construction, infrastructure, household appliances, automobiles, steel furniture, etc.

Zinc Oxide: Most widely used zinc compound, zinc oxide is used in the vulcanization of rubber,

as well as in ceramics, paints, animal feed and pharmaceuticals, and many other products and

processes. A special grade of zinc oxide has long been used in photocopiers.

Zinc Die Castings: Zinc is an ideal material for die casting and is extensively used in hardware,

electrical equipments, automotive and electronic components.

Rolled Zinc: Zinc sheet is used extensively in the building industry for roofing, flashing and

weathering applications. Zinc sheet is also used in graphic art to make plates and blocks, as well as

battery callots and coinage.

Alloys: Zinc is extensively used in making alloys such as brass, an alloy of copper & zinc.

4. Safety Department:

Safety is a degree of control over hazards. Workers working in the factory are exposed to all sorts

of dangers so some personal protective equipment are available to protect them head to toe such as-

1. Ear Muff

2. Dust Mask

3. Face Shield

4. Gas Mask

5. Gloves

6. Goggles

7. Helmets

8. Leg Guard

9. Respirators

10. Rubber Apron

11. Rubber Gum Boots

12. Safety Ball

13. Safety shoes

Factorizing the entire operation to safe sequence efficiency in carefully performing the work. For

the welfare of group in which the worker attached, you and your own protection of job. Accidents

are caused due to following reasons

1. Unsafe Condition

2. Unsafe Act

Unsafe Condition: Such condition includes leaking gases & unprotects able machines, not

furnace, professional hazard, occupational diseases prevailing in the industry.

Unsafe act: These accidents happen due to laziness and negligence of the rules while he is on duty.

General Rules and Safety

1. Be alert on work & do it in attention.

2. Working place path should be clean.

3. Always use safety belt while climbing up ladders.

4. Take help from skilled worker to start machine.

5. Waste dirt should not be scattered in Narrow Street.

6. Scattered thing stored in proper place.

7. Before eating meal, wash hands & clean nail.

8. While working in hot place put on asbestos gloves.

9. Don't store guiding wheel at moisturized place, don't use them at higher than rated speed.

10. Don’t pass beyond the chain block or come when heavy loading is being done.

5. Zinc smelting steps in Various plant:

5.1) ROASTER PLANT

This is the first department, where the treatment of zinc is being done. Zinc sulphide is carried on

conveyer belts to the furnace. Here zinc-sulphide is converted into zinc oxide or calcine. SO 2 is a

by product of the process which is further used for obtaining H2SO4 in the Acid Plant. SO2 is

harmful so it is recovered by the quenching tower, PGCT, WGT.

Procedure-

Zinc concentrate handling system consists of two Phases i.e. phase 1 and phase 2.

PHASE I- Concentrate comes from ZM and RAM.

These concentrate are Transported by trucks and dumpers from mines and all unloaded on surface

grizzly of under ground hopes. Series of belt conveyors Transfer the concentrate from under

ground hopper to blend storage yard. Unloading on different heaps is done with the help of triple

conveyor. The storage yard is divided into parts for ZM, RDM and RAM.

To avoid wind losses water is sprayed through sprayer or manually by using Hose pipes. This also

to maintain required moisture in concentrates. The water spraying is done manually whenever

needed.

PHASE 2-

Activities of phase 2 are as follows- Zinc Concentrates of different mines from storage yard are

charged in the underground hoppers (104A and 104B) in the required ratio with the help of Terex..

Mixing ratio is decided by availability of concentrate from different units. The criterion of mixing

is marinating Zinc and Sulphur Content min. 50% and 28% respectively. Also feed back from

reaching and electrolysis about cathode sheet quantity is taken into consideration. Zinc dross (from

Zinc melting section is also added along with concentrates in very little quantity.

The mixture of different concentrate (called blend) is transported to bins of Roaster- 1 and II and

with the help of series of belt conveyors and a vibrating screen which allows only under size

material to go bins.

Oversize materials is ground in a hammer Mill and charged back to 104 A and 104 B hoppers. An

electro magnet is provided on one of the Conveyors to attract and separate iron pieces, if any going

to bins. Water is also sprayed on 107 & 108 belt Conveyors to increase moisture is blend feed.

Minimum 8% moisture is maintained in blend feed. Sample is drawn from extraction belt and is

analyzed for moisture twice in a shift.

All operation of starting the conveyors is done by an operator deputed at control room of blend

yard. Zinc blend is taken from the blend bin through extraction belt to rotary table feeder and high

speed feed machine. Then blend is fed to fluidized bed roaster through furnace feed hole. Zinc

blend is roaster to produce Calcine and sulpher dioxide gas.

2Zns+3O2 2Zno+ 2So2+ heat

Air for roasting of Zinc blend supplied through roaster air blower continuously to roaster furnace

through nozzles. Calcine form furnace comes out through over flow, under flow, boiler, cyclones

and hot gas precipitator which is sent to reaching plant through screw conveyors is air cooled and

other conveyors are water cooled for cooling of calcine.

Hot gases with fine calcine particles coming from roaster furnace pass waste heat boiler in which

hot gases are cooled, and steam is produced by circulation of DM water in boiler tube bundles.

Water is also circulated in furnace cooling coil installed in furnace hearth to maintain the desired

bed temperature.

Gases leaving waste heat boiler are passed through cyclone to remove the calcine particles and then

passed through hot gas precipitator to remove the fine particles of calcine by the application of

electric field.

Gases leaving the hot gas precipitator are passed through scrubbing tower to cool down. In

scrubbing tower spraying of water is done from top and gases entre from the bottom. Dust free

gases from the scrubbing tower are passed through star cooled for further cooling. The gases

leaving from star cooler are passed though electro filter to remove the miss completely.

Extraction Belt

Rotary Table

Feed Machine

Roaster Furnace

Water heater boiler

Cyclone

HGP

Gas Scrubber

Star Cooler

Wet Esp. /EF I &II Stage

Hg. Removal Tower

SO2 Bearing gases

Feed Bin

ID Fan

To acid plant

Calcine

Calcine

Calcine

Calcine

Air Blower

Sodium Silicate

Sodium silicate dosing: - Sodium silicate dosing is done in scrubber circulating water to remove

fluoride from So2 bearing gases as per following reaction –

Na2 SiO3 + 6HF Na2 SiF6 + 3H2O

The dosing system consists of a sodium silicate storage tank, dilution tank, pump tank and dosing

pump (2Nos.). Dilute solution of 5% strength is prepared in dilution tank and dosing sate is decided

as per fluoride content in concentrate as per instruction of day Mgr (p)/ Mgr (p).

Block Diagram of Roaster and Gas Cleaning Plant

5.2) BOILER CIRCUIT

Boiler circuit is use to generate the steam using the heat which is dissipated from Roaster plant.

In Boiler, dematerialized water is use. This dematerialized water is supplied from DM. Plant.

Feeding of water in boiler is control and supplied by an electric/ turbo feed pump. Circulation of

boiler water is done by electric/turbo circulation pump through roaster furnace coil, boiler bundles

and bundles of guide pipe.

Excess steam in exported to leaching plant. In case of power failure or any emergency turbo

feed/turbo circulation pump may be run with the help of generated steam to feed the water in boiler

drum and water can be circulated in cooling coils and boiler bundles. In boiler water following

values are maintained.

Chemical i.e. sodium sulphite, trisodium phosphate caustic soda are prepared and injected in

Derator discharge through I dosing pump.

5.3) ACID PLANT:

Standard Minimum Maximum

Ph 10.5 8.0 13.0

Alkalinity 200ppm - 500ppm

Hardness Nil - Nil

Chloride Nil - 50ppm

Sulphite 10ppm 5ppm -

Phosphate 20ppm 10ppm -

Figure: Block diagram of Roaster Plant

SO2 Bearing Gases

Drying Tower

SO2 Blower

Heat exchanger

I II Converter

IV III

Heat exchanger

Final absorption tower

Stack

Heat exchanger

IPAT

Acid storage tank

Figure: Block diagram of acid plant

Production of sulphuric acid in acid plant 1 and 2 is done.

Sulphuric acid thus produced is stored in acid storage tank labeled as A, B and C product sulphuric

acid is stored in acid storage tank D&E.

The acid is supplied to the leaching plant or in tanks A, B, C of acid plant No.2 through a transfer

pump of capacity 1000MT, 1000MT and 1500MT respectively. Finally gases are discharged

through chimney to atmosphere.

Minimum 97% acid concentration is maintained in acid storage tanks. Acid of supply tank A, B &

C is analyzed and analysis is recorded in register No. ZSD/R&A/Reg.07. If any how the acid

concentration is found below 97% in any supply tanks, this acid is recycled back to acid circulation

tank to build up the concentration to 97% min. or raise the concentration by mixing with fresh

product acid of higher concentration or alternatively this acid is used for internal consumption in

leaching, RTP or DM plant

Pre-Heater:- The preheater is to generate flue gases heating the catalyst mass up to 365oc (min),

when starting the plant after shut down. Hot air is obtained by burning LDO with air in combustion

chamber of preheater.

LDO is supplied to the burner, where combustion takes place and air is heated. The air for

atomization and combustion is provided by combustion blower. Air for dilution is provided by

dilution blower. The hot air is passed through the tube of heat exchanger whereas the sulphur

dioxide bearing gases passes on shall side and get heated. The fuel gas is vented to atmosphere

through the stack.

5.4) LEACHING & PURIFICATION PLANT

Leaching is selective dissolution of ore minerals/oxides, alkalis or solution of other reagent

according to condition adjusted in a manner to leave max gangue in soluble residue. Calcine come

in hopper with the help of bucket elevator. From hopper calcine is coming to roller conveyor

through a rotatry valve. By adjusting speed of rotatry valve calcine rate can be increased or

decreased. The calcine if in excess can be stored in silos. The average rate of calcine consumption

is 11 MT/ hr., whereas rate of solution supplied is 90m3/hr. This corresponds to 140-150 MT of

Zinc ingots.

The department consists of following sections:

1. Neutral leaching

2. acid Leaching

3. Purification

4. Residual treatment plant

5. cadmium plant

NEUTRAL LEACHING:

The iron leached from fine particles of ZnO.Fe2O3 will be precipitated as hydroxides in neutral

medium according to equation.

Fe2(SO4)3+3ZnO+3H2O → 2Fe(OH)3+3ZnSO4

The Zn in calcine is present as:

ZnO - 81 to 83% ZnSO4 – 6 to 7 %

ZnS - 1 to 2% ZnOFe2O3 – 10%

In first stage of neutral leaching solution will be slightly acidic& PH is 2.8 to 3.2.So main equation:

MeO+ H2SO4 → MeSO4+H2O

Where Me→ Zn, Cu, Ni, Co, Mg, Pd.

The PH solution discharged after completion of leaching is 4.5 & at that PH acidity is negligible.

ACID LEACHING:

This is carried in carriers having capacity of 45 m3.The underflow from neutral leaching

containing dissolved ZnO & ZnO.Fe2CO3 is leached with spent electrolyte to PH of 2.8. Alternate

carriers are provided with heating coil through which steam is passed. Reaction time is 5 hr. most

soluble oxide go into solution. The overflow containing 30-40 GPL of Zn is sent to neutral

leaching. Underflow is pumped to two drum filters.

PURIFICATION:

Purification of Zinc sulphate is necessary as certain elements even if amounting to milligrams per

liter may cause:-

1. Hydrogen evolution and dissolution of Zinc by reducing impurities Fe++, Co, Ni, As etc.

2. Zinc is electro positive to ordinary metal like copper, iron, cadmium etc. therefore during

electrolysis these elements coil tends to deposit along with zinc, affecting the purity of the

final product and current efficient.

Principle:

Keeping temperature to 80 to 85 degree C, the clear overflow from the natural thickener is fed into

the purification stage. The purpose of this stage is to remove base metal impurities like copper,

cadmium, nickel etc. which are harmful to electrolysis of zinc. All these elements are removed by

precipitation with the help of Zinc dust. Zinc being placed higher then all the elements in the

electromechanical series of elements, displaces them from solution of sulphates as per the

following reaction:

Zn + MnSO4 ZnSO4 + Mppt

LeachingCalcine

Joaosite

Neutralization

Thickning

Acid leaching

Residual Treatment

Jarosite filteration

Purification

Purified neutralSolution

Cd recovery

Zerosite cake to ETP

Cd Pencil

U/F

O/f

U/F

U/F

Thickening

Figure: Process flow chart of Leaching plant

Also addition of antimony tratarte and copper sulphate speed up the rate of reaction to ensure

complete removal of impurities.

5.5) RESIDUE TREATMENT PLANT

The Zinc ferrite ZnO. Fe2O3 in the acid thickness under flow gets leached in the conversion and

simultaneously the leached iron is precipitated as Zerosite. Here the section is carried out in there

lead or brick line rectors of 300 meter cube capacity each, at a temperature of 95 to 100C. Some

amount of MnO2 is also added to take care of reducing impurities. In this operation Zinc ferrite is

precipitated as complex known as Zerosite.

The Zerosite slurry from this reaction is settled in the DORR with county current decantation.

Zerosite from the last thickener continues repulped and filtered again to recover water soluble Zinc.

The cake is subsequently repulped and pumped in ETP where it is neutralized to8ph and discarded

into lagoon . The over low from the DORR contains 80-100 GPL iron is send to neutral leaching.

5.6) ZINC DUST PLANT

The use of Zinc dust is for internal consumption, use in purification process to remove CuSO4,

CdSO4, CoSO4, NiSO4 in leaching plant.

The reaction follows as-

Zn + MeSO4→ ZnSO4 + Me↓

Due to higher electropositive element, the process of Zn dust involves the following:

1. Zn melting

2. Zn vaporization

3. Condensation

4. Production Technology

For Zn vaporization a voltage of 1000-11000C is created with the help of two electrodes, one at top

& other at base. It is filled with molten Zn.

For condensation N2 gas is being used. The N2 gas & five particles of Zn dust is being passed N2

gas is passed containing five particles of Zn dust.

The Zn dust is get at bottom. The body of condenser is made up of mild steel. The separate Zn dust

cyclone is being used. Again to separate Zn dust from N2 gas it is passed through a bag filter.

Production rate is about 6- 6.5MT/day. The pressure of N2 gas is about 600 cubic feet. The

consumption to produce 1 MT Zn dust is about 825 – 850 KW/hr.

5.7) ZINC ELECTROLYSIS & MELTING:

Electrolysis of ZnSO4 solution takes place in electrolysis cells with Al as cathode & Pb as anode.

The reaction can be represented as

ZnSO4→ Zn2+ + SO42-

SO4 + H2O→ H2SO4 + ½O2

Zn ions migrate towards the cathode and get deposited in form of sheets whereas O2 is given off at

anode. As SO2 ions, this results in formation of Sulphuric Acid. The oxygen is liberated oxides the

manganous sulphate in solution to MnO2 which deposit on the anode surface as anode mud which

is then cleaned out periodically.

5.8) SOLUTION COOLING & STORAGE

Neutral electrolyte form purification shall be available at 60 – 700C as hot purification process had

adopted for expansion the neutral solution is fed direct to atmospheric coolers where direct solution

is cooled to 850C. Two coolers have been provided for the purpose of which one would stand by.

The HZL has adopted “HAMON 50 BELEO” Belgion design for atmospheric coolers which are

being used in nos. of other plants in the world.

ZnSO4 solution that has to be cooled is taken through main feeder & it is distributed through

reinforced polyester pipes on which is stainless steel 316 spraying nozzles are fixed. Above this,

drift eliminated are arranged in two layers in form of layers of PVC waves. These waves,

assembled in panes are easily removable through top of coolers. The cooler is fitted with forced

draught fan fitted with FRP blades. The fan stock is also made up from FRP & stainless steel

grating provides protection to fan inlet. The fan is driven pulley & belt by two speed motors. These

coolers are used to reduce the temperature from 420C to 350C.

Electrolysis takes place in lead lines concrete cells which are connected electricity by means of Cu

bus bars in series parallel system for flow of current in existing cell house. The cells are arranged

in 40 rows. Each row has 6 cells with 27 Al cathode and 28 lead anodes. After expansion, each cell

will have its own feed system & its own independent discharge of electrolytes.

6. Central Workshop:

The Zinc smelter, Debari has a central workshop for securing & repairing of different mechanical

equipments such as pumps, fans, mechanical conveyors, hoists etc. The central workshop consists

of following shops:

1. Machine shop

2. Welding shop

3. Smiting shop

4. Wood shop

6.1) MACHINE SHOP :-

Machine shop is the biggest shop in all shops it consists of various machines. They are-

1. lathe machine

2. Drilling machine3. Slottering machine4. Shaper machine5. Punching machine6. Shearing machine7. Power sack saw8. milling machine9. Grinding machine

10. Hydraulic Pressure machine11. Pipe bending & sheet rolling machine

Repairing of many parts is done in central workshop on different machines.

6.2) WELDING WORKSHOP

Breaking parts which are easily weld able are welded in welding workshop. There are two types of

welding is done. 1. Arc welding & 2. Gas welding So two types of sets are:

1. Arc welding set

2. Gas welding set

Arc welding is most extensively employed method for joining metal parts where source of heat is

electric arc.

Gas welding is done by a combustible gas with air or oxygen in a concentrate flame at higher

temperature.

6.3) SMITHY SHOP

In Smithy shop some parts are manufactured which are to be used in different plants main

components of this shop are: 1. Furnaces 2. Anvil

6.4) WOOD WORKSHOP

In Wood workshop some process happens such as planning, grooving, cutting of wood used in

different plants on different machines available in workshop.

6.5) ELECTRICAL REPAIR SHOP

The Zinc Smelter, Debari has an electrical repair shop. Electricity is very important for an industry

without it no work can be performed now a day. So electrical equipments are also used widely in

industry. To repair electric material, electrical repair shop is to be used.

ACTIVITIES OF ELECTRICAL REPAIR SHOP :-

1. Overhauling & Rewinding of LT motors up to 250 KW.

2. AMC of cooling machine3. Refrigerators4. Window A/C5. Package A/C6. Water coolers etc.

3. 432 lines EPBAX definity, tata telecom , PA system

1. contract scheduling , finalization and execution

2. Procurement

3. Resource planning & estimation

4. Indenting – formulation & specifications of electrical items

5. Technical evolution of electrical items (tech bids)

6. Handling quality, assurance/ inspection of incoming material/ spares

7. Safety assurance – By improving the house keeping & all PPE’s so safety equipments as

per IE rules.

8. Also associate with working for reduction in spares consumption, inventory control by

exploration & reclamation

9. Generation of power reports weekly/ monthly & preparation of liability statements.

7. Instrumentation Department

Zinc smelter instrumentation department analyses, controls and records various process parameters

and on the basis of these parameters various processes are being controlled.

For ideal process execution, productivity and pollution control the instrumentation department

plays an extremely important role. Here the following parameters are considered for process

execution and recording is made and computerized as and when desired.

1. Punching Clocks: - Using these clocks the attendance of all employees and their in and out

times are recorded and computerized as well.

2. Weigh Bridge: - Computerized weigh bridges are used to weigh raw materials and the

finished goods ready for dispatch. Electronics feed machines are used to feed raw materials

and chemicals in the plant.

3. Automatic Casting Machine and Bundle Machines: - Using these machines zinc ingots

are casted automatically and are bundled in lots.

4. Flow Measurement: - Water meters, Rota meters magnetic flow meters, differential flow

transmitters and vertex flow meters are the various devices implemented to carry out flow

measurements. Controlling is done through controller and control valve.

5. Pressure Measurement: - For the filled indication pressure gauges and manometers are

used. Processes are being controlled by pressure transmitters, recorders, indicators,

controllers and control valves.

6. Level Measurements: - For level control indication and recording of various process

elements the devices basically used are level switches. Level transmitters and ultrasonic

transmitters.

7. Temperature Measurement: - For temperature controlling, recording, indication and

alarming temperature recorders, indicators, controllers and pyrometers are used. As primary

sensors thermocouples and RTD are also used with these temperature recorders, indicators,

controllers and pyrometers.

8. Ph conductivity, Acid Concentration and Gas analysis: - Using automatic Ph channel

analyzer, concentration analyzer and conductivity analyzer the above mentioned parameters

are automatically controlled recordedZinc Smelter, Debari instrumentation, department deals

with maintenance, calibration, repairing, erection and commissioning.

Maintenance and calibration work is done according to the norms specified by ISO 9001 and ISO

14001 standards.

For maintenance , Calibration and repairing sufficient equipments are available with the instrument

department. They are as follows:

1) Avometers

2) Milliampere and millivolt sources and measuring instruments

3) Variable ac-dc power supplies

4) Portable temperature indicators

5) Resistance boxes

6) CRO

7) Frequency generators

8) Heart communicators

9) Flow calibrator

10) Conductivity calibrators

11) Dead Weight Testers

Instrumentation department is fragmented into three sections:-

1) CENTRAL REPAIR SHOP: In this section indenting, material inspection and typical

repairing are done. Moor cake plant and effluent treatment plant are also supervised by

this section.

2) ROASTER ACID SECTION: Acid – I, Acid – II, roaster – I, roaster – II, DM plant and

compressor house are supervised by this section.

3) LEACHING AND PURIFICATION SECTION: Weigh bridge, Zinc Dust, neutro

leaching, purification, DG set zinc electrolysis are supervised by this section.

PROJECT :

STUDY OF PROGRAMMABLE LOGIC CONTROLLERS

1. Introduction:

A programmable logic controller (PLC) is an industrial computer control system that

continuously monitors the state of input devices and makes decisions based upon a custom

program, to control the state of devices connected as outputs. They are specially designed

architecture in both their central units (the PLC itself) and their interfacing circuitry to field devices

(input/output connections to the real world).

These devices, also called programmable controllers or PLCs are the hub of many manufacturing

processes. These are solid-state members of the computer family, using integrated circuits instead

of electromechanical devices to implement control functions. They are capable of storing

instructions, such as sequencing, timing, counting, arithmetic, data manipulation, and

communication, to control industrial machines and processes. Figure 1-1 illustrates a

conceptual diagram of a PLC application.

FieldInputs

Process or Machines

ProgrammableController

Measure ControlFeedback from

sensors/switchesConnections to

actuators

Figure 1-1. PLC conceptual application diagram.

Almost any production line, machine function or process can be automated using a PLC. The

speed and accuracy of the operation can be greatly enhanced using this type of control system. But

the biggest benefit in using a PLC is the ability to change and interfere with the operation or

process while collecting and communicating vital information.

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.

2. Need of PLC:

Relay and its disadvantages:

Modern control systems still include relays, but these are rarely used for logic. A relay is an

electrically operated switch. Current flowing through the coil of the relay creates a magnetic field

which attracts a lever and changes the switch contacts. The coil current can be on or off so relays

have two switch positions and they are double throw (changeover) switches. Relay provides

electrical isolation between two circuits. The coil of a relay passes a relatively large current,

typically 30mA for a 12V relay, but it can be as much as 100mA for relays designed to operate

from lower voltages.

Relays are usually SPDT or DPDT but they can have many more sets of switch contacts, for

example relays with 4 sets of changeover contacts are readily available.

FieldOutputs

When a relay is used to switch a large amount of electrical power through its contacts, it is

assigned by a special name: contactor. Contactors typically have multiple contacts. Perhaps the

most common industrial use for contactors is the control of electric motors.

A basic contactor will have a coil input (driven by either an AC or DC supply depending on the

contactor design). The coil may be energized at the same voltage as the motor, or may be

separately controlled with a lower coil voltage, at present they are better suited to control by

programmable controllers(but not for developing logic) and other lower-voltage devices.

Contactors range from a breaking current of several amps and 24 V dc to thousands of amps and

many kilovolts.

Disadvantages:

Relays cannot switch rapidly (except reed relays), transistors can switch many times per

second.

Relays use more power due to the current flowing through their coil.

Relays require more current than many ICs can provide, so a low power transistor may be

needed to switch the current for the relay's coil.

Before the PLC, control, sequencing, and safety interlock logic for manufacturing automobiles was

accomplished using hundreds or thousands of relays, timers, and drum sequencers and dedicated

closed-loop controllers. The process for updating such facilities was very time consuming and

expensive, as the relay systems needed to be rewired by skilled electricians. So the primary goal of

introducing PLC was to eliminate the high costs associated with inflexible, relay-controlled

systems. The specifications required a solid-state system with computer flexibility able to

(1) survive in an industrial environment,

(2) be easily programmed and maintained by plant engineers and technicians, and

(3) be reusable.

Hence the Programmable logic control came into picture which fulfills all requirements, i.e.

reusability, expandability, programmability, and ease of use in an industrial environment.

3. PLC past and present:

3.1) History of plc:

The first PLCs offered relay functionality, thus replacing the original hardwired relay logic, which

used electrically operated devices to mechanically switch electrical circuits. The first

programmable controllers were more or less just relay replacers. Their primary function was to

perform the sequential operations that were previously implemented with relays. These operations

included ON/OFF control of machines and processes that required repetitive operations, such as

transfer lines and grinding and boring machines. Some of the feature of first introduced Plc were:

- A typical unit housing a CPU and I/O was roughly the size of a 19” television set. Through the

1980s and early 1990s, modular PLCs continued to shrink their size while increasing in capabilities

and performance.

- communications protocol allowed PLCs to communicate over some specific standard cabling.

- the controller does not know the position of the output device during the control sequence.

- even simple motion control required an expensive PLC module so cost was much higher..

- only Relay Ladder logic programming was supported.

Although PLC functions, such as speed of operation, types of interfaces, and data-processing

capabilities, have improved throughout the years, but they are simple to use and maintain.

3.2 The present state

PLCs are also now well-equipped to replace stand-alone process controllers in many applications,

due to their ability to perform functions of motion control, data acquisition, RTU (remote telemetry

unit) and even some integrated HMI (human machine interface) functions. key characteristics of

plc at present are:

- smaller PLCs have been introduced in nano and micro classes that offer features equivalent to

larger PLCs. These are capable of motion control, remote connectivity and more.

- the serial communications remain popular and reliable, but now Ethernet is fast becoming the

popular communication media with advantages of network speed, ease of use, built-in

communications setups etc.

- high-speed counting capabilities and high-frequency pulse outputs built into the controller,

making them a suitable solution for both open & closed-loop control.

- almost every PLC now-a-days can support two graphical and two textual PLC programming

language standards:

Ladder logic (graphical).

Function block diagram (graphical).

Structured text (textual).

Instruction list (textual).

The latest technology gives the PLC a faster, more powerful processor with more memory at less

cost. These advances have also allowed the PLC to expand area of command and take on new tasks

like communications, data manipulation and high-speed motion without giving up the rugged and

reliable performance expected from industrial control equipment.

4. Advantages of PLC

Inherent Features Benefits

Solid-state components • High reliability

Programmable memory • Simplifies changes & Flexible controlSmall size • Minimal space requirements

Microprocessor-based • Communication capability• Higher level of performance• Higher quality products• Multifunctional capability

Software timers/counters • Eliminate hardware• Easily changed presets

Software control relays • Reduce hardware/wiring cost• Reduce space requirements

Modular architecture • Installation flexibility• Easily installed• Reduces hardware cost• Expandability

Variety of I/O interfaces • Controls a variety of devices• Eliminates customized control

Remote I/O stations • Eliminate long wire/conduit runs

Diagnostic indicators • Reduce troubleshooting time• Signal proper operation

Modular I/O interface • Neat appearance of control panel• Easily maintained• Easily wired

Quick I/O disconnects • Service without disturbing wiring

System variables • Useful management/maintenance stored in memory data

• Can be output in report form

5. PLC features:

The following list describes some latest PLC hardware enhancements:

• Faster scan times are achieved using new advanced microprocessor and electronic technology.

• Small, low-cost PLCs which can replace four to ten relays have more power than their

predecessor, the simple relay replacer.

• High-density input/output (I/O) systems provide space-efficient interfaces at low cost.

• Intelligent, microprocessor-based I/O interface can provide distributed processing. Some of the

interfaces include CANbus, fieldbus, ASCII communication, positioning, host computer, and

language modules (e.g., BASIC, Pascal).

• Mechanical design improvements include rugged input/output enclosure and input/output systems

that makes the terminal an integral unit.

• Special interfaces allow certain devices to be connected directly to the controller. Some of them

are thermocouples, strain gauges, and fast-response inputs.

All of these hardware enhancements have led to the development of programmable controller

families like the one shown in Figure

Like hardware advances, software advances, have led to more powerful PLCs:

• PLCs now support object-oriented programming tools and multiple languages based on the IEC

1131-3 standard.

• Even small PLCs have powerful instructions, which extend the area of application for these small

controllers.

• High-level languages, such as BASIC and C, is present in some controllers’ modules to provide

greater programming flexibility when communicating with peripheral devices and manipulating

data.

• Advanced functional block instructions for ladder diagram instruction sets, provide enhanced

software capability using simple programming commands.

• Improved diagnostics and fault detection facility to include machine diagnostics along with

simple system diagnostics, which diagnose failures or malfunctions of the controlled machine or

process also diagnosing controller malfunctions..

Improved and simplified data handling and manipulation instructions to accommodate complex

control and data acquisition applications that involve storage, tracking, and retrieval of large

amounts of data.

6.Internal architecture of PLC :

The basic internal architecture of a PLC is shown in figure. It consists of a central processing unit

(CPU) containing the system microprocessor, memory, and input/output circuitry.

The CPU controls and processes all the operations within the PLC. It is supplied with a clock with

a frequency of typically between 1 and 8 MHz. This frequency determines the operating speed of

the PLC and provides the timing and synchronization for all elements in the system.

The information within the PLC is carried by means of digital signals. The internal paths along

which digital signals flow are called buses. In the physical sense, a bus is just a number of

conductors along which electrical signals can flow. It might be tracks on a printed circuit board or

wires in a ribbon cable. The CPU uses the data bus for sending data between the constituent

elements, the address bus to send the addresses of locations for accessing stored data and the

control bus for signals relating to internal control actions. The system bus is used for

communications between the input/output ports and the input/output unit.

6.1) The CPU

The internal structure of the CPU depends on the microprocessor concerned. In general they have:

An arithmetic and logic unit (ALU) which is responsible for data manipulation and

carrying out arithmetic operations of addition and subtraction and logic operations of AND,

OR, NOT and EXCLUSIVE-OR.

Memory, termed registers, located within the microprocessor and used to store information

involved in program execution.

A control unit which is used to control the timing of operations.

6.2) The buses

The buses are the paths used for communication within the PLC. The information is transmitted in

binary form, i.e. as a group of bits (a byte or a word) with a bit being a binary digit of 1 or 0, i.e.

on/off states. Each of the bits is communicated simultaneously along its own parallel wire. The

system has four buses:

The data bus carries the data used in the processing carried out by the CPU. A

microprocessor termed as being 8-bit has an internal data bus which can handle 8-bit

numbers. It can thus perform operations between 8-bit numbers and deliver results as 8-bit

values.

Figure : Internal Architecture of PLC

The address bus is used to carry the addresses of memory locations. So that data stored at a

particular location can be accessed by the CPU either to read data located there or put, i.e.

write, data there. It is the address bus which carries the information indicating which

address is to be accessed. If the address bus consists of 8 lines, the number of 8-bit words,

and hence number of distinct addresses, is 28 = 256. With 16 address lines, 65 536

addresses are possible.

The control bus carries the signals used by the CPU for control, e.g. to inform memory

devices whether they are to receive data from an input or output data and to carry timing

signals used to synchronize actions.

The system bus is used for communications between the input/output ports and the

input/output unit.

6.3) Memory

There are several memory elements in a PLC system:

System read-only-memory (ROM) to give permanent storage for the operating system and

fixed data used by the CPU.

Random-access memory (RAM) for the user’s program and for data. This is where

information is stored on the status of input and output devices and the values of timers and

counters and other internal devices. The data RAM is sometimes referred to as a data table

or register table. Part of this memory, i.e. a block of addresses, will be set aside for input

and output addresses and the states of those inputs and outputs. Part will be set aside for

preset data and part for storing counter values, timer values, etc.

Possibly, as a bolt-on extra module, erasable and programmable read-only-memory

(EPROM) for ROMs that can be programmed and then the program made permanent.

The programs and data in RAM can be changed by the user. All PLCs will have some amount of

RAM to store programs that have been developed by the user and program data. However, to

prevent the loss of programs when the power supply is switched off, a battery is used in the PLC to

maintain the RAM contents for a period of time. After a program has been developed in RAM it

may be loaded into an EPROM memory chip, often a bolt-on module to the PLC, and so made

permanent. In addition there are temporary buffer stores for the input/output channels.

6.4) Input/output unit

The input/output unit provides the interface between the system and the outside world, allowing for

connections to be made through input/output channels to input devices such as sensors and output

devices such as motors and solenoids. It is also through the input/output unit that programs are

entered from a program panel. Every input/output point has a unique address which can be used by

the CPU.

The input/output channels provide isolation and signal conditioning functions so that sensors and

actuators can often be directly connected to them without the need for other circuitry. Electrical

isolation from the external world is usually by means of optoisolator (the term optocoupler is also

often used). Figure5 shows the principle of an optoisolator. When a digital pulse passes through the

light-emitting diode, a pulse of infrared

radiation is produced. This pulse is detected by

the phototransistor and gives rise to a voltage

in that circuit. The gap between the light-

emitting diode and the phototransistor gives

electrical isolation but the arrangement still allows for a digital pulse in one circuit to give rise to a

digital pulse in another circuit. Figure Optoisolator

The digital signal that is generally compatible with the microprocessor in the PLC is 5 V d.c.

However, signal conditioning in the input channel, with isolation, enables a wide range of input

signals to be supplied to it. A range of inputs might be available with a larger PLC, e.g. 5 V, 24 V,

110 V and 240 V digital/discrete, i.e. on−off, signals (Figure 6). A small PLC is likely to have just

one form of input, e.g. 24 V.

The output from the input/output unit will be digital with a level of 5 V. However, after signal

conditioning with relays, transistors or triacs, the output from the output channel might be a 24 V,

100 mA switching signal, a d.c. voltage of 110 V, 1 A or perhaps 240 V, 1 A a.c., or 240 V, 2 A

a.c., from a triac output channel (Figure 7). With a small PLC, all the outputs might be of one type,

e.g. 240 V a.c., 1 A. With modular PLCs, however, a range of outputs can be accommodated by

selection of the modules to be used.

Figure: Input Levels

Outputs are

specified as being of relay type, transistor

type or triac type.

With the relay type, the signal from the PLC output is used to operate a relay and is able to

switch currents of the order of a few amperes in an external circuit. The relay not only

allows small currents to switch much larger currents but also isolates the PLC from the

external circuit. Relays are, however, relatively slow to operate. Relay outputs are suitable

for a.c. and d.c. switching. They can withstand high surge currents and voltage transients.

The transistor type of output uses a transistor to switch current through the external circuit.

This gives a considerably faster switching action. It is, however, strictly for d.c. switching

and is destroyed by over current and high reverse voltage. As a protection, either a fuse or

built-in electronic protections are used. Optoisolators are used to provide isolation.

Triac outputs, with optoisolator for isolation, can be used to control external loads which

are connected to the a.c. power supply. It is strictly for a.c. operation and is very easily

destroyed by over current. Fuses are virtually always included to protect such outputs.

6.5) Types of Input and outputs :

6.5.1) Discrete input:

A discrete input also referred to as a digital input, is an input that is either in an ON or OFF

condition.

Figure Output levels

6.5.2) Analog Input:

An analog input is an input signal that has a continuous signal. Typical analog inputs may vary

from 0 to 20 milliamps, 4 to 20 milliamps, or 0 to 10 volts. In the following example, a level

transmitter monitors the level of liquid in a tank. Depending on the level transmitter, the signal to

the PLC can either increase or decrease as the level increases or decreases.

6.5.3) Discrete Output:

A discrete output is an output that is either in an ON or OFF condition. Solenoids, contactor coils,

and lamps are examples of actuator devices connected to discrete outputs. Discrete outputs may

also be referred to as digital outputs. In the following example, a lamp can be turned on or off by

the PLC output it is connected to.

6.5.4) Analog Output:

An analog output is an output signal that has a continuous signal. The output may be as simple as a 0-10

VDC level that drives an analog meter. Examples of analog meter outputs are speed, weight, and

temperature. The output signal may also be used on more complex applications such as a current-to

pneumatic transducer that controls an air-operated flow-control valve.

6.6) Input/output terminology:

6.6.1) Sensors:

A sensor is a device that converts a physical condition into an electrical signal for use by the PLC.

Sensors are connected to the input of a PLC. These act as input to PLC.

1. Mechanical switches:

A mechanical switch generates an on-off signal or signals as a result of some mechanical input

causing the switch to open or close. These contact switches are available as normally open and

normally closed They are used as motion limit switches and part present detectors.

2. Proximity switch

Proximity switches are used to detect the presence of an item without making contact with it. There

are a number of forms of such switches, some being only suitable for metallic objects.

The eddy current type of proximity switch has a coil which is energized by a constant alternating

current and produces a constant alternating magnetic field. When a metallic object is close to it,

eddy currents are induced in it

3. Reed switch

Reed switch has two non touching springy strips of ferromagnetic material enclosed in a plastic

case. When a magnet or current-carrying coil is brought close to the switch, the strips attract and

switch closed.

4. Capacitive Sensors

These sensors can detect metallic or non metallic material by generating signal according to its

dielectric change or we can say capacitive change

5. Optical Sensors:

Optical sensors require both a light source (emitter) and detector. Emitters will produce light beams

in the visible and invisible spectrums using LEDs and laser diodes. Detectors are mostly built with

photodiodes or phototransistors. The emitter and detector are positioned so that an object will block

or reflect a beam when present; according to which signal is generated.

6. Ultrasonic Sensors:

An ultrasonic sensor emits a sound above the normal hearing threshold of 16 KHz. The time that is

required for the sound to travel to the target and reflect back is proportional to the distance to the

target.

7. Temperature sensors:

A temperature sensor can be used to provide an on–off signal when a particular temperature is

reached. For e.g. switching of a bimetallic strip when a particular temperature is reached. Another

and most important examples of temperature sensor are RTD and thermocouple.

RTD (Resistance Temperature Detectors): These devices have positive temperature coefficients

that cause resistance to increase linearly with temperature. A platinum RTD might have a

resistance of 100 ohms at 0oC, which will increase by 0.4 ohms/°C. The total resistance of an RTD

might double over the temperature range. Mostly their max temperature sensing rage varies from -

200oC to max. of 650oC.

Thermocouple: The thermocouple consists of two dissimilar wires A and B forming a junction. In

a thermocouple, the two metals are joined together at junctions with different temperatures. This

temperature differential creates a voltage across the thermocouple—a phenomenon known as the

Seebeck effect. Temperature T1, the hot junction, is the temperature being measured, while T2, the

cold junction, is the reference temperature. As temperature T1 increases, the voltage differential

(emf) between materials A and B increases in proportion to the temperature.

6.6.2) Actuators:

Actuators drive motions in mechanical systems. Most often this is by converting electrical energy

into some form of mechanical motion. These act as output to PLC.

1. Solenoid:

Solenoids are the most common actuator components. The basic principle of operation is there is a

moving ferrous core (a piston) that will move inside wire coil when the coil is excited. Normally

the piston is held outside the coil by a spring. Applications of solenoid include pneumatic values

and car door openers.

2. Relay:

Solenoids form the basis of a number of output control actuators. Such an actuator is the relay.

When the output from the PLC is switched on, the solenoid magnetic field is produced and pulls on

the contacts and so closes a switch or switches Thus the relay might be used to switch on the

current to a motor.

3. Valves:

Figure: Stepper motor with 4 poles

The flow of fluids and air can be controlled with solenoid controlled valves. A solenoid controlled

valve is shown in figure. The solenoid is mounted on the side. When it is actuated, it will drive the

central spool right to close the inlet path B (in figure). In unactuated position, it will return back to

original position by the spring to close path A.

4. Motors:

Motors are common actuators, but for logical control applications their properties are not that

important. Typically logical control of motors consists of switching low current motors directly

with a PLC, or for more powerful motors using a relay or motor starter.

5. Stepper motors:

The stepper or

stepping motor

is a motor that

produces

rotation through

equal angles, the

so-termed steps,

for each digital

pulse supplied to

its input. If it is used to drive a continuous belt, it can be used

to give accurate linear positioning. Such a motor is used with

computer printers, robots, machine tools and a wide range of

instruments where accurate positioning is required.

Figure: Solenoid valve

Others:

There are many other types of actuators including those on the brief list below.

Heaters - They are often controlled with a relay and turned on and off to maintain a temperature

within a range.

Lights - Lights are used on almost all machines to indicate the machine state and provide feedback

to the operator. Most lights are low current and are connected directly to the PLC.

Sirens/Horns - Sirens or horns can be useful for unattended or dangerous machines to make

conditions well known. These can often be connected directly to the PLC.

5. Sourcing and sinking

The terms sourcing and sinking are used to describe the way in which d.c. devices are connected

to a PLC. With sourcing, using the conventional current flow direction as from positive to negative,

an input device receives current from the input module, i.e. the input module is the source of the

current (Figure 8(a)). If the current flows from the output module to an output load then the output

module is referred to as sourcing (Figure 8(b)).

With sinking, using the conventional current flow direction as from positive to negative, an input

device supplies current to the input module, i.e. the input module is the sink for the current (Figure

9(a)). If the current flows to the output module from an output load then the output module is

referred to as sinking (Figure 9(b))

Figure 8: Sourcing

Timers Counters

Figure 9 Sinking

7. The PLC system Hardware:

Typically a PLC system has the basic functional components of processor unit, memory, power

supply unit, input/output interface section, communications interface and the programming device.

Figure shows the basic arrangement.

1.

2. The

processor unit or central processing unit (CPU) is the unit containing the microprocessor

and this interprets the input signals and carries out the control actions, according to the

program stored in its memory, communicating the decisions as action signals to the

outputs.

3. The power supply unit is needed to convert the mains a.c. voltage to the low d.c. voltage

(5 V) necessary for the processor and the circuits in the input and output interface modules.

4. The programming device is used to enter the required program into the memory of the

processor. The program is developed in the device and then transferred to the memory unit

of the PLC.

5. The memory unit is where the program is stored that is to be used for the control actions to

be exercised by the microprocessor and data stored from the input for processing and for

the output for outputting.

6. The input and output sections are where the processor receives information from

external devices and communicates information to external devices. The inputs might thus

be from switches or other sensors such as photo-electric cells, temperature sensors, or flow

sensors, etc. The outputs might be to motor starter coils, solenoid valves, etc. Input and

output devices can be classified as giving signals which are discrete, digital or analogue.

7. The communications interface is used to receive and transmit data on communication

networks from or to other remote PLCs (Figure 3). It is concerned with such actions as

Figure : The PLC system

device verification, data acquisition, synchronization between user applications and

connection management.

8. There are four major types of Timers; on-delay timer -set the output after a set delay when

the logic has been true previously but turn off immediately, for off-delay timer it is vice-

versa. A retentive timer will sum all of the on or off time for a timer, even if the timer never

finished. A nonretentive timer will start timing the delay from zero each time.

9. There are two basic Counter types: count-up and count-down. When the input to a count-

up counter goes high (true) the accumulator value will increase by 1. If the accumulator

value reaches the preset value the counter bit will be set. For count-down counting I decree

by one until preset value is reached to set counter.

8. Principle of Operation:

A programmable controller consists of two basic sections; the central processing unit & the

input/output interface system. The operation of a programmable controller is relatively simple. The

input/output (I/O) system is physically connected to the field devices that are encountered in the

machine or that are used in the control of a process. These field devices may be discrete or analog

input/output devices, such as limit switches, pressure transducers, push buttons, motor starters,

solenoids, etc. The I/O interfaces provide the connection between the CPU and the information

providers (inputs) and controllable devices (outputs).

During its operation, the CPU completes three processes: (1) it reads, or accepts, the input data

from the field devices via the input interfaces, (2) it executes, or performs, the control program

stored in the memory system, and (3) it writes, or updates, the output devices via the output

interfaces. This process of sequentially reading the inputs, executing the program in memory, and

updating the outputs is known as scanning.

The input/output system forms the interface by which field devices are connected to the controller

The main purpose of the interface is to condition the various signals received from or sent to

external field devices. Incoming signals from sensors (e.g., push buttons, limit switches, analog

sensors, selector switches, and thumbwheel switches) are wired to terminals on the input interfaces.

Devices that will be controlled, like motor starters, solenoid valves, pilot lights, and position

valves, are connected to the terminals of the output interfaces. The system power supply provides

all the voltages required for the proper operation of the various central processing unit sections.

9. PLCs versus Other Types of Controls:

A PLC is not the only choice for controlling a process. Sticking with only basic relays may be of a

benefit depending upon our application. Also the PLC vs. PC debate has been going on for a long

time. More often though it doesn't come down to an one sided situation but involves a mix of

technologies.

1. PLC vs. Relay:

In the early times of programming PLCs it was still questionable if a PLC was necessary over just

relay control. With PLC prices going down, size shrinking, and performance of PLCs improving

over the years this has become less of a battle. Yet the designer has to ask themselves if a PLC is

really overkill for their application.

2. PLC vs. Dedicated Controller:

A dedicated controller is a single instrument that is dedicated to controlling one parameter such as

a PID controller measuring a temperature for heating control. They have the advantages of an all in

one package, typically with display and buttons. This can be a very good thing to use in simple

applications. A PLC these days can compete price wise and functionally with these controllers

especially if more than one controller is needed. PLCs offer a greater degree of flexibility too

because the can be programmed to handle all sorts of different scenarios.

3. PLC vs. PC (Personal Computers):

The PLC vs. PC debate has been going on for years. They both have their pros and cons. What often

happens is that the two are used for their strengths in different parts of the factory.

12. Advancements in PLC:

1. Artificial Intelligence:

Artificial intelligence means make a system able to take decision according to the action being

performed. The software programs that form an AI system are developed using the knowledge of

experts in the field where the system will be applied.

AI techniques can be implemented through a PLC-based process control system. These techniques

will define the methods for implementing AI into the process. The result will be a system that can

successfully diagnose, control, and predict outcomes based on resident knowledge and program

sophistication.

In AI system (see figure), it must receive all information about system maintenance, faults along

with their probable causes and possible solutions etc. for developing database. According to this

database and predefined rules for governing process, AI system maintain the process regular and

generate the possible cause of failure, its solution, method to reduce loss or even generate new rule

for maintaining the process regular indicating the with minimum effect on production quantity &

quality after indication of the failure.

Applying AI techniques to a control system usually involves adding hardware and software to the

system. The complexity of the AI program varies depending on how much fault detection is

desired.

2. Fuzzy Logic

Fuzzy logic is a branch of artificial intelligence that deals with reasoning algorithms used to match

human thinking and decision making in machines, and for the information that can't be represented

in binary form. Fuzzy logic associates a grade, or level, with a data range, giving it a value of 1 at

its maximum and 0 at its minimum.

Action TakenKnowledge Acquisition

Engineer or Expert

Database: Knowledge information

Inference Engine: Control Strategy, solution

Feedback Information

User

Figure: Artificial Intelligence system

For example, the statement “the air feels cool” is not a discrete statement. In the case of the cool

air, a PLC with fuzzy logic capabilities would interpret both the level of coolness and its

relationship to warmth to assure that “cool” means somewhere between hot and cold.

For logic development various rules are developed taking those components for which the logic has

to be developed. According to them the controller performs the task of maintaining the

temperature.

3. Human-Machine Interface:

A Human-Machine Interface or HMI is the apparatus which presents process data to a human

operator, and through which the human operator controls the process. An HMI is usually linked to

the SCADA system's databases and software programs, to provide trending, diagnostic data, and

management information such as scheduled maintenance procedures, logistic information, detailed

schematics for a particular sensor or machine, and expert-system troubleshooting guides. The HMI

system usually presents the information to the operating personnel graphically, in the form of a

mimic diagram. This means that the operator can see a schematic representation of the plant being

controlled.

For example, a picture of a pump connected to a pipe can show the operator that the pump is

running and how much fluid it is pumping through the pipe at the moment. The operator can then

switch the pump off. The HMI software will show the flow rate of the fluid in the pipe decrease in

real time. Mimic diagrams may consist of line graphics and schematic symbols to represent process

elements, or may consist of digital photographs of the process equipment overlain with animated

symbols.

4. Networking:

When there is huge amount of data present then sometime processor scan time get affected worst

consuming large amount of memory and complicating the program. So, LAN configuration, in

which all data is passed to a host computer that performs all data processing eliminates these

problems. Also instead of single controller several controller may work together or simultaneously,

distributing data evenly through network. To use the distributed processing approach, a local area

network and the PLCs attached to it must provide the following functions:

• communication between programmable controllers

• upload capability to a host computer from any PLC

• download capability from a host computer to any PLC

• reading/writing of I/O values and registers to any PLC

• monitoring of PLC status and control of PLC operation

13. Distributed Control System (DCS) :

A Distributed Control System is an elaborate, monolithic network of microprocessors that

controlled various aspects of a process system. A distributed control system (DCS) refers to a

control system usually of a manufacturing system, process or any kind of dynamic system, in

which the controller elements are not central in location (like the brain) but are distributed

throughout the system with each component sub-system controlled by one or more controllers. The

entire system of controllers is connected by networks for communication and monitoring.

13.1) Elements-a brief view

A DCS typically uses custom designed processors as controllers and uses both proprietary

interconnections and Communications protocol for communication.

Input & output modules form component parts of the DCS.

The processor receives information from input modules and sends information to output

modules.

The input modules receive information from input instruments in the process (a.k.a. field)

and transmit instructions to the output instruments in the field.

Computer buses or electrical buses connect the processor and modules through multiplexer

or demultiplexers. Buses also connect the distributed controllers with the central controller

and finally to the Human-Machine Interface (HMI) or control consoles.

Elements of a distributed control system may directly connect to physical equipment such

as switches, pumps and valves or may work through an intermediate system such as a

SCADA system.

13.2) Application:

DCS is a very broad term used in a variety of industries, to monitor and control distributed

equipment.

Electrical power grids and electrical generation plants

Environmental control systems

Traffic signals

Water management systems

Oil refining plants

Chemical plants

Pharmaceutical manufacturing

Sensor networks

Dry cargo and bulk oil carrier ships

They are complex and expensive, and typically used proprietary hardware and software including

control languages, so only the company that built them could service and support them. And once

the system in place, it is difficult to adapt as your process requirements changed over time. But,

they are capable of handling the largest and most complex processing systems, making them a

major step forward for continuous processing industries like Mining & Smelting, Power & Energy,

Oil & Gas, Water & Wastewater, and Pulp & Paper.

14. Hybrid Systems:

In the last decade, both historic DCS and PLC companies have moved toward a space that both call

"hybrid," in which they attempt to offer the power and complexity of DCSs and the flexibility,

openness and low cost of PLC systems.

DCS companies have done this by reducing the footprint of their systems while PLC companies

have begun linking their components together to create more complete systems. But though many

were commercially successful, these "hybrid systems" have never fully delivered on the original

hybrid promise. For one thing, the DCS hybrids have been unable to tailor their systems to become

modular enough to work with both OEMs & End Users and scalable, flexible enough to handle

applications that range from small to large. In addition, the speeds of high speed sequential or

discrete processes — sometimes measured in the tens of milliseconds — are typically too fast for

DCS hybrids to accommodate making applications like packaging or metal stamping or simple

motor control difficult if not impossible to control. So a hybrid plant with batch, continuous and

discrete environments or a large continuous processing plant with high speed sequential control

needs as well still had to acquire a second process system for their discrete areas, with all the extra

cost, integration problems, increased training and maintenance that entailed.

Conclusion

Every aspect of industry—from power generation to automobile painting to food packaging—uses

programmable controllers to expand and enhance production. Today, the two technologies share

kingdoms as the functional lines between them continue to blur. We now use each where the other

used to rule. However, PLCs still dominate high-speed machine control, and DCSs hold in

complex continuous processes.

The 30 days training stint at HZL proved to be a fruitful and learning experience as it provided an

opportunity for me to work in a rapidly developing organization striving for excellence in its

operations and services.

The Project team, with whom I worked in my time spent here, not only cleared my basics

knowledge but also explained the systematic and efficient manner in which they carry out their day

to day operations for achieving customer satisfaction. The hierarchy at HZL insures that there is

accountability and transparency in the system and the projects undertaken are completed on or

before time.

Bibliography

Day to day notes

The PLC theory book – L.A. Brayan, K.A. Brayan

Programmable logic controllers – Hugh Jack

Programmable logic controllers – W. Bolton

Internet file links:

1. http:// Programmable Logic Controllers (PLCs) Specifications.htm

2. http:// Programmable logic controller - Wikipedia, the free encyclopedia.htm

3. http:// DCS vs PLC.htm

4. http:// Distributed control system - Wikipedia, the free encyclopedia.htm etc.