CHAPTER -1

INTRODUCTION

1.1 COMPANY PROFILE

The Aditya Birla Group is a conglomerate named after Aditya Vikram Birla, Headquaters in Aditya Birla Center in Worli, Mumbai, India. It operates in 40 countries with more than 120,000 employees worldwide. The group was found by Seth Shiv Narayan Birla in 1857. The groupinterests in sectors such as viscose staple fiber, metals, cement, v Corporation Limited previously known as Birla Jute and Industries Limited, belong to the Miscose filament yarn,branded apparel,carbon black, chemicals, fertilizers, insulators, financial services, telecom, Bpo and it services.

1.2 ORIGIN & GROWTH

The roots of the Aditya Birla Group date back to the 19th century in the picturesque town of Pilani, setamidst the Rajasthan desert. It was here that Seth ShivNarayan Birla started trading in cotton, laying the foundation for the House of Birla.Through India's arduous times of the 1850s, the Birla business expanded rapidly. In the early part of the 20th century, our Group's founding father, Ghanshyamdas Birla, set up industries in critical sectors such as textiles and fibre, aluminium, cement and chemicals.

Fig 1.1- Plant View From Cement Silo Top

As a close confidante of Mahatma Gandhi, he played an active role in the Indian freedom struggle. He represented India at the first and second round-table conference in London, along with Gandhiji. It was at "Birla House" in Delhi that the luminaries of the Indian freedom struggle often met to plot the downfall of the British Raj.

1

Ghanshyamdas Birla found no contradiction in pursuing business goals with the dedication of a saint, emerging as one of the foremost industrialists of pre-independence India. The principles by which he lived were soaked up by his grandson, Aditya Vikram Birla, our Group's legendary leader.

1.3CORPORATE SYMBOL

The corporate symbol of concentric circles around a triangle represents the very multi dimensional nature. The apex of triangle is a visual representation of the force that drives the entire corporation the unifying force in search of excellence. The various sub-business units are diverse in interest and operation. But they are held together by centripetal drive. The circle represents the inspiration to explore new frontiers of growth.

1.4 PRODUCT CHART

1.5 AWARDS

2

J U T E D I V I S I O N

C E M E N T D I V I S I O N

A U T O T R I M D I V I S I O N

B I R L A C A R B I D E & G L A S S

B I R L A V I N O L E U M

B I R L A S Y N T H E T I C S

ADITYA BIRLA CORPORATION LIMITED

Awards

C A P E X I L A w a r d s e v e r y y e a r , s i n c e 1 9 9 0 .

“Bhama Shah Samman” from the Rajasthan Government for Educational Activities for Aditya Birla Cement Works in 1996-97.

VEC-IIT, Madras recognized Aditya Birla Cement Works For “Excellence In Improving Machinery Health Condition” in 1997.

“Workers Education Trophy” awarded by central Board of Workers Education, Udaipur Ministry of labor, Government of India, for Aditya Birla Cement Works in 1998-99 and again in 2001-02 .

“Lal Bahadur Shastri Memorial National Award” for Excellent Pollution Control Implementation by Aditya birla Cement Works in 2002-03.

“Best Supporting Core Plant” by Regional Training Centre, Nimabhera in 1998-99, 2000-01 & 2001-02.

“Awards to Captive Mines” (Safety Week Celebration in Udaipur Region) by DGMS, Udaipur 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002.

1.6 CEMENT DIVISION

The cement division of aditya Birla Corporation Limited has six plants as under table. Chittor units aditya Birla share is around Rs.350 Crores, which is 34% of the company’s turnovers. These plants manufacturing the verity of cement like:

a) Ordinary Portland Cement (OPC) of 33,43 and 53 Gradeb) Pozzolana Portland Cement (PPC) with china clay and Fly ash.

3

CHAPTER-2

BASIC LAYOUT OF CEMENT2.1 MINING

The process of mining which is use dhereto extract Limes one from the Earths Opencast mining. The process of mining includes three things:

Prospecting: It is the process of finding potential at place from where very useful & bulk quantity of limestone can be extracted

Fig 2.1- Mining

Drilling: After providing with a better place for mining, the process of drilling takes place in which the place is drilled with the drilling machines, for inserting the dynamites.Blasting: After drilling holes, this place is blasted by blasting materials inserted inside the drilled part to break the huge rocks into pieces.

2.2 CRUSHER

These pieces of rocks are brought near to the crusher & are further processed.

Fig2.2-Raw Material Processing

4

The crusher crushes these collected rocks into fine pieces of 50 mm size. It just breaks down the huge rocks into compatible sizes with Impact /hammer mechanismsm

2.3 PRE-HOMOGENIZATION OF RAW MATERIAL:

In this process this crushed material l is arranged in the form of piles with the help of stacker, to make it available for picking it up for further processing.

Fig 2.3-Stacker

Here definite pile size is fixed. Laterite [Iron ore] is also mixed in this process. This piled material is then reclaimed by the Reclaimed.

Fig 2.4-Reclaimer

The function of Reclaimed is just to reclaim the definite amount of material from the pile & provide it to conveyor belt, which conveys this picked up material to the raw-mill. Reclaimed ensures equal distribution of material over conveyor belt. Before conveying the material to raw-mill, the magnetic separation process takes place to remove all the magnetic material accompanying the raw material.

5

2.4 RAW MILLIn Raw-mill section, this conveyed material is transferred into hopper

which feeds and regulated amount of material to the mill. This feeding is carried out with TFG (Triple Feed Gate), which is a hydraulic gate used to avoid overfeeding of material in mill. Raw-Mill consists of large rollers, which is used to grind this crushed material into fine powder. This fine powder is collected & is stored in Raw-mill silos, which is called Raw-Meal for Kiln..

Fig 2.5 -Vertical Roller Mill

The raw materials are usually quarried from local rock, which in some places is already practically the desired composition and in other places requires the addition of clay and limestone, as well as iron ore, bauxite or recycled materials. The individual raw materials are first crushed, typically to below 50 mm. In many plants, some or all of the raw materials are then roughly blended in a "prehomogenization pile." The raw materials are next ground together in a raw mill. Silos of individual raw materials are arranged over the feed conveyor belt. Accurately controlled proportions of each material are delivered onto the belt by weigh- feeders. Passing into the raw mill, the mixture is ground to raw mix. The fineness of raw mix is specified in terms of the size of the largest particles, and is usually controlled so that there are less than 5%-15% by mass of particles exceeding 90 μm in diameter. It is important that the raw mix contain no large particles in order to complete the chemical reactions in the kiln, and to ensure the mix is chemically homogeneous. In the case of a dry process, the raw mill also dries the raw materials, usually by passing hot exhaust gases from the kiln through the mill, so that the raw mix emerges as a fine powder. This is conveyed to the blending system by conveyor belt or by a powder pump. In the case of wet process, water is added to the raw mill feed, and the mill product is a slurry with moisture content usually in the range 25-45% by mass. This slurry is conveyed to the blending system by conventional liquid pumps.

6

2.5 PREHEATER

In this the Raw-Meal stored in raw mill silo is first preheated before feeding it to Kiln section. For heating this material here, mainly pulverized Coal / Pet coke is used which is procured from various places. This imported coal / pet coke is first crushed in crusher, then grinded to fine powder in vertical coal mill & then this powdered coal is stocked in coal mill silos.

Fig 2.6-Preheater Section

A proper amount of coal powder is sucked from coal mill silos & then fired through burners for preheating the raw meal at Pre-calciner and Kiln.

2.6 KILN

Aditya birla Cementplant has a 75 mtrs long kiln having diameter of 5.0 mtrs for manufacturing OPC clinker supplied by M/s polysiusThyssenkrupp Germany. The clinker is produced by burning the finely ground raw meal (Mixture of Limestone+ Additives like Bauxite & Laterite) known as kiln feed in a rotary kiln. The temperature in the burning zone is usually 1400-1450 deg.C and the residence time in the kiln is 25 minutes. The process taking place in the kiln system consist of a temperature dependent decomposition of the raw material minerals according to the nature, followed by a recombination of the liberated free reactive oxides forming clinker minerals, the most important being C3S(Alite - Tricalcium Silicate), C2S (Belite - Dicalcium Silicate), C3A (Tricalcium Aluminate)and C4AF (TetracalciumAlumino Ferrite). The clinker formation sequence as a function of the temperature can briefly be characterised as follows:

Table 2.1 Clinker Formation Sequence

Temp. Description of Process Type of

7

(deg.C) Reaction100 Drying & evaporation of free water Endothermic

100-400 Elimination of absorbed water Endothermic400-750 Decomposition of clay minerals Endothermic

Kaolinite – Metakaolinite600-900 Decomposition of Metakaolinite to reactive oxides Endothermic600-1000 Decomposition of carbonates to free reactive oxides Endothermic

800-1300 Combination of reactive oxides to form intermediate clinker minerals Exothermic

1300-1380 Formation of aluminates & ferrites Endothermic1250-1450 Formation of Alite (C3S) Endothermic

The process takes place in an oxidising environment. Among the chemical process described above, the reaction rate of the first five groups of reaction comprises the decomposition of the

Fig 2.7-General Layout of Rotary Kiln

minerals in the raw meal and the liberation of reactive oxides is determined by the rate of the heat transfer to the solid material in 6-stage ILC preheater. The reaction rate of the two last groups of clinker forming reactions is determined in the rotary kiln by the contact rate of the mutual chemical reactive compounds present in different solid phases and later in the burning zone by the diffusion of the reactive compounds in the clinker melt. The overall chemical reactions transforming the mixture of raw material minerals in the raw meal to the mixture of the clinker minerals in the clinker is endothermic (heat consuming). Clinker formed in kiln is cooled inside the Polytrack cooler from 1450 deg.C to around 110 oC and then it is stored in clinker silo having a storage capacity of 45000 tons.

2.7 COOLER SECTION

8

In this section, hot clinker coming out from kiln is fed. This hot clinker is cooled from air stream produced by various cooler fans. This cooled clinker is stacked in clinker stock piles. The clinker is then fed to cement mill for further processing.

2.8 CEMENT MILL

The final manufacturing stage at a cement plant is the grinding of cement clinker from the kiln, mixed with some 4-6% gypsum, into a fine powder. It is important to obtain a certain specific surface for the finished cement so that hydration can take place and concrete strength develops within a reasonable time. In addition to the specific surface, also the particle size distribution influences the strength properties especially the late strength.

Fig2.8-CementMillAt Aditya Birla Cement, we have two combi circuit grinding ball mills with roller press having capacity of 200 tph each. Two dosimat feeders feed the material, clinker & gypsum. Gypsum is mixed with clinker during grinding operation for retarding setting time and to increase the workability of cement. Clinker and gypsum in required proportions are fed to roller press the output of the roller press pass through V-separator and product of V-separator feed to the single chamber ball mill through the inlet chute of the mill. The mill inlet consists of a chute for material and a pipe for sucking in ventilation air. The air intake is provided with a throttle valve so as to ensure a suitable negative pressure at the inlet and to avoid dust nuisance around the surrounding area. The grinding is affected by grinding media.. A charge consisting of 25, 20 and 15 mm steel balls is used in chamber for fine grinding. Total approximately 155 MT grinding media is loaded in each mill.

At the outlet of the mill, the ground material flows through an outlet grate to dynamic separator by mechanical conveyors, for fine separation as grinding system is closed circuit mill. Grinding in close circuit makes it possible to obtain a very finely ground cement. Another advantage is that it is easy to change from one grade of cement to another grade by adjustment of the separator speed . Cement produced in closed

9

circuit mill has narrow particle size range and the quantity of 3 to 30 microns fraction is more in comparison to open circuit mill, resulting in to more late strength. The mill ventilation air carries a small portion of the fine material, which is dedusted in highly efficientBag-House.

Fig 2.9-Cement Mill Processing

Finished product with separator air is passed through multiclones where finished product is separated and stored in cement silos with the help of mechanical conveyor.

2.9PACKING PLANT

This is the final processing plant in which cement is packed into sacks. There are 3 packers in the plant. each packer consists of 8 nozzles. The speed of rotation of the nozzle machine is 4.5 rpm i.e. 36 bags come out every minute out of the plant. they are then sent to either truck loading or wagon loading through conveyer.

Fig 2.10 Rotary Packer Machine

2.10 DISPATCH

Once the production of cement is complete, the finished product is transferred using bucket elevators and conveyors to large, storage silos in the shipping

10

department. Most of the cement is transported in bulk by railway, truck, or barge, or in 50 kg multiwall paper bags. Bags are used primarily to package masonry cement. Once the cement leaves the plant, distribution terminals are sometimes used as an intermediary holding location prior to customer distribution. The same types of conveyor systems used at the plant are used to load cement at distribution terminals.

Fig 2.11-Truck Loading

Fig 2.12-Wagon Loading

2.11 CENTRAL CONTROL ROOM (CCR)

To accomplish this long process for definite amount of mixing & process control for controlling various processes of the plant, as it is operated fully automatically, that is, no manual operation is needed, for which an upgraded & better control system is needed. And for making the control system functional & to take care of various electronic measuring systems, where the field electronics have its necessity. The plant is equipped with PLCs (Programmable Logic Controls) controlling the whole processes of the plant from a single office namely CCR (Central Control Room) with PCs controlling the operation of each machine in the plant all around 24 hours driving each & every electrical machines with definite supplies & frequency for accomplishing cement manufacturing.

11

Fig 2.13-Central Control Room

12

27

CHAPTER-3INSTRUMENTATION & AUTOMATION IN CEMENT

3.1. HISTORY & ADVANCES IN AUTOMATION:The modern cement plant today is equipped with latest technology of automation.

The automation of cement plant is comparable to any industry such as steel, petroleum

etc.

Some of the rate feats of Indian Cement Industry are :

First programmable controller was introduced in 1978.

Thyristor/Transistor based analogue variable speed AC drive in various applications.

First fuzzy control for cement got commissioned in 1987.

Most powerful advance SCADA/DCS are in use since 1986-2000.

The cement plants in India are very competitive today; they are very efficient in terms

of thermal & electrical energy consumption, in terms of productivity.

Some of the latest Plants commissioned in 2004 are operating at 72kWh/ton of

cement. Today we can control plant from remote distance. The same can be

demonstrated at Chittorgarh.

The CCR of typical Cement Plant of 1 million tons/annum capacity is equipped with

atleast 4-Operator Stations (OS).

Seven colour desktops are available for Kiln, raw mill & Cooler burning view and

some communication facility such as Phones, Wireless and PA system etc.

3.2. NEEDS OF PROCESS CONTROL AUTOMATION:Every Industrial Process has three types of main flows:

Material Flow

Energy flow

Information Flow

So the aim of Plant Automation is to identify the Information flow i.e. to take related

information and control Material & Energy Flow in desired manner.

3.3. BENEFITS OF AUTOMATION:

27

Increase in production

Improvement in quality

Reduction in cost

Optimal use of available resources

Environmental pollution control

Safety

3.4. TYPICAL AUTOMATION MEASUREMENT IN CEMENT

PLANT : Crusher–

o BRG Temperature

Stacker & Reclaimer –

o Maximum level of material

o Maximum travel

Ball Mill –

o BRG Temperature

o Oil flow & Pressure

o Sound level

Vertical Mill –

o Vibration

o Presence of metal

Kiln System –

o BRG Temperature

o Shell & Lining temperature

o Position (L.S. UP, DN)

Larger Motors –

o WNG & BRG Temperature

o Cooling Air flow & PR

Elevators –

o Alignment

27

o Speed Monitor

Conveyors –

o Alignment (Belt Sway)

o Speed Monitor

TABLE 3.1. CRUSHER

S.No. Equipment Location Application1. Apron Feeder Crusher To measure & control speed of apron

feeder2. Laterite Feeder Crusher To measure & control the feed of Laterite

(Additive)3. Wireless

CommunicationCrusher, Stacker,

ReclaimerTo send & receive information from & to

CCR from moving equipments.4. Power Measurement Power Calculation

TABLE 3.2. RAW MILL

S.No. Equipment Location Application1 Weight Feeders Inlet to Mill To feed & control limestone & Laterite to raw mill

inlet in raw mill.2 Metal Detector To detect metal pieces on belts.3 Metal Separator To separate metal pieces from raw material which is

detected by metal detector.4 Power Mill Power

TABLE 3.3. ESP, GCT & PREHEATER

S.No. Equipment Location Application Other information1. Thermocouple Bottom of

cycloneFor cyclone

material temperature.

K Type

2. Thermocouple top of cyclone

For cyclone gas temperature.

K Type

3. Draught(PR Tx.)

Bottom of cyclone

For cyclone bottom draught

Gives idea of material feeded in cyclone & also idea of cyclonic

action taking place4. ESP panel ESP Panel To measure &

control kV & mA

27

TABLE 3.4. BELTS

S.No. Equipment Location Application1. Speed Moniter Tail End To sense the rotation.

TABLE 3.5.PACKING PLANT

S.No. Equipment Location6 Application Other information

1. Level sensors In various hoppers/tanks, feeding

MAT. To PKR.

To sense level E &H/ Sapcon make

2. Proximity Switches

Bag conveying belts To sense belt running

3. Limit Switches

Packer For providing various safeties in PKR like

pendulum switch, pull cord surrounding PKR etc.

4. Solenoid Valves

Packer For performing various actions

Involved in bag filling to evacuation.

TABLE 3.6.KILN & COOLER SECTION

S.No. Equipment Location Application Other information

1. Thermocouple Kiln inlet For measuring Kiln inlet temperature.

K Type

2. RTD Kiln Roller For measuring kiln inlet temperature

Shoe type RTD

3. RTD Kiln Gear Box

For measuring kiln roller brg temperature

Simple PT-100 RTD

4. RTD Kiln Motor For measuring kiln G.Box oil temperature

Simple PT-100 RTD

5. Analyzers Kiln Inlet For measuring kiln motor WDG & BRG. Temperature

02 0-10%, co 0-2%, nox 0-3000 PPM

6. Tacho Kiln Drive Kiln Speed Hubner make7. Solid flow

FeederC.F.Silo Material feed to Kiln J&N, Ranchi

8. ESP panel ESP panel To measure & control kV & mA

Hind Rectifier controller

27

CHAPTER- 4SENSOR

A sensor is a device that measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument. For example, a mercury-in-glass thermometer converts the measured temperature into expansion and contraction of a liquid which can be read on a calibrated glass tube. A thermocouple converts temperature to an output voltage which can be read by a voltmeter. For accuracy, all sensors need to be calibrated against known standards.

4.1. USE

Sensors are used in everyday objects such as touch-sensitive elevator buttons and lamps which dim or brighten by touching the base. There are also innumerable applications for sensors of which most people are never aware. Applications include cars, machines, aerospace, medicine, manufacturing and robotics.A sensor's sensitivity indicates how much the sensor's output changes when the measured quantity changes. For instance, if the mercury in a thermometer moves 1 cm when the temperature changes by 1 °C, the sensitivity is 1 cm/°C. Sensors that measure very small changes must have very high sensitivities.Ideal sensors are designed to be linear. The output signal of such a sensor is linearly proportional to the value of the measured property. The resolution of a sensor is the smallest change it can detect in the quantity that it is measuring.

4.2. LEVEL SENSOR

4.2.1. GENERAL APPLICATION OF LEVEL SENSOR :

Level Sensors designed to provide accurate and reliable level information of Solids (Powder & Lumps), Liquids and Slurry applications for point level detection in storage Bins, Silos, Hoppers, Tanks and any other vessels where material is stored, processed and discharged even at high temperature/pressure.

Figure 4.1 Level Sensor

27

4.2.2. FUNCTION OF LEVEL SENSOR :The oscillator generates low-power RF signal which is used to provide signals

equal in frequency phase and amplitude to both, active section and shield section of the probe. The signal applied to the shield is held constant by use of compensating amplifier. The detector is then used to compare the fixed shield signal with active signal which varies with the dielectric constant of the material in contact with the probe. Difference in the signals compared by the detector cause the output relay to activate. The contacts of the output relay to when activated are used to indicate the presence or absence of material in the vessel at the probe level.

27

CHAPTER-5

RESISTANCE THERMOMETER

Resistance thermometers, also called resistance temperature detectors or resistive thermal devices (RTDs), are temperature sensors that exploit the predictable change in electrical resistance of some materials with changing temperature. As they are almost invariably made of platinum, they are often called platinum resistance thermometers (PRTs).

5.1. TYPES

Film thermometers have a layer of platinum on a substrate; the layer may be extremely thin,

perhaps one micrometer. Advantages of this type are relatively low cost and fast response. Such devices have improved in performance although the different expansion rates of the substrate and platinum give "strain gauge" effects and stability problems.

Wire-wound thermometers can have greater accuracy, especially for wide temperature ranges. The coil diameter provides a compromise between mechanical stability and allowing expansion of the wire to minimize strain and consequential drift.

5.2. FUNCTIONResistance thermometers are constructed in a number of forms and offer greater

stability, accuracy and repeatability in some cases than thermocouples. While thermocouples use the Seebeck effect to generate a voltage, resistance thermometers use electrical resistance and require a power source to operate. The resistance ideally varies linearly with temperature. Resistance thermometers require a small current to be passed through in order to determine the resistance. The two most common ways of measuring industrial temperatures are with resistance temperature detectors (RTDs) and thermocouples. Selection criteria: - Temperature, time, size, and overall accuracy .

Figure 5.1 Film thermometers Film thermometers Film

thermometers

Figure 5.2 Wire-wound thermometers

27

CHAPTER-6

PROGRAMMABLE LOGIC CONTROL

6.1. INTRODUCTION

A programmable logic controller (PLC) or programmable controller is a digital computer used for automation of electromechanical processes, such as control of machinery on factory assembly lines, amusement rides, or lighting fixtures. PLCs are used in many industries and machines, such as packaging and semiconductor machines. Unlike general-purpose computers, the PLC is designed for multiple inputs and output arrangements, extended temperature ranges, immunity to electrical noise, and resistance to vibration and impact. Programs to control machine operation are typically stored in battery-backed or non-volatile memory. A PLC is an example of a real time system since output results must be produced in response to input conditions within a bounded time, otherwise unintended operation will result.;

6.2. WHAT IS PROGRAMMABLE LOGIC CONTROL ?

A programmable logic controller (PLC) is a special data processor used as controller for machines in industrial processes. As a part of process control, a programmable logic controller is used to monitor input signals from a variety of input points which report events and conditions occurring in a controlled process. During the execution of a stored control program, they read inputs from the controlled process and, per the logic of the control program, provide outputs to the controlled process.On primary basis PLC is having following advantages over any other controlling element invented before its invention :-

Cost effective specially for controlling complex systems. Flexible and can be re-applied to control other systems quickly and without much

manipulation in the programme. Computation abilities allow us do more sophisticated control. Trouble shooting allows us to make programme more efficiently, hence reduce

down time.The purpose of a PLC was to directly replace electromechanical relays as logic elements, substituting instead a solid-state digital computer with a stored program, able to emulate the interconnection of many relays to perform certain logical tasks.

276.3. BLOCKS OF PLC

6.3.1. Inputs

6.3.2. Output

6.3.3. Memory

6.3.4. Central Processing unit(CPU)

6.3.5. Power Supply

6.3.1. INPUTSInput signals are real time signals. They may be analog\digital, low\high

frequency etc. But in general case they are represented as various voltages to the programmable controller they can be from Switches, Pushbuttons, Proximity sensors etc.

6.3.2. OUTPUTSOutput signals are generally a digital signal which is applied to three categories of

output devices. Discrete (Pilot lights, Solenoid Valves etc.) Register (Drive Panel meters) Analog (Drive signals to variable speed)

Figure 6.1 PLC Block Diagram

27

6.3.3. MEMORYIt is the main storage area of a PLC, which is used to hold the set of instruction to

be executed by the processor/programming devices. Its size may very from 256 bytes to several mega bytes.

6.3.4. CPU Central processing unit is the brain of PLC controller. CPU itself is one of the

microcontroller. It perform task which are necessary to fulfill the function of PLC. Earlier it was 8 bit microcontroller such as 8051 but now these are 16 and 32 bit microcontrollers. CPU takes care of following functions :-

Scanning I/O devices (BUS traffic control) Program execution Memory Read/Write External device communication

6.3.5. POWER SUPPLYPower supply unit converts line voltage to a required voltage which is needed by

solid state components. Most PLC controllers work on 24 volt DC to 220 volt DC.

6.4. MAIN ELEMENTS OF PLC

While manufacturing as well as while programming a PLC following things are necessary to keep in mind both by the manufacturer and user, they are :

6.4.1. Ladder Logic 6.4.2. Programming6.4.3. PLC Connection 6.4.4. Ladder Logic Inputs6.4.5. Ladder Logic Outputs

6.4.1. LADDER LOGICLadder logic is the main programming method used for PLC’s. Ladder logic has

been developed to mimic relay logic. By selecting ladder logic as the main programming method, the amount of retraining needed for engineers and trades people was greatly reduced. Modern control system still include relays, but these are rarely used for logic. The example is shown in figure 2 does not show the entire control system, but only the logic. When we consider a PLC these are inputs, outputs and the logic. Figure 2 shows a more complete representation of PLC.

Here, there are two inputs from push buttons. We can imagine the inputs as ctivating 24 volt DC relay coils in the PLC. This is turn drives an output relay that

27

switches 115 volt AC, which will turn on a light. Note, in actual PLC’s inputs are ver relays, but outputs are often relays.

The ladder logic in the PLC is actually a computer program that the user can defined and modify. Notice that both of the input push buttons are normally open, but the ladder logic inside the PLC has one normally open contact, and one normally closed contact. Ladder logic in the PLC does not needs to match the input and outputs.The figure shows a simple ladder logic which consist of one NO-contact, NC-contact and a contactor, can be consider as a simple relay controller.

6.4.2. PROGRAMMINGThe first PLC’s were programmed with a technique that was based on relay logic

wiring schematics. This eliminated the need to teach the electrician, technicians and engineers how to program a computer – but, this method has stuck and it is the most common technique for programming PLC today. Another example of ladder logic is shown in figure.To interpret the diagram imagines that the power is on the vertical line of the left hand side, we called this the hot rail. On the right hand side is the neutral rail. In the figure 3 there are two rungs, and on each rung there are combinations of inputs (two vertical lines)

and outputs (circle). If the input are opened or closed in the right combination the power can flow from the hot rail, through the inputs, to power the outputs, and finally to the neutral rail. An input can come from a sensor, switch or any other type of sensor. An output will be some device outside the PLC that is switched ON or OFF, such as lights or motors. In the top rung the contact are

normally open and normally closed. This means if input A is on and input B is off,

Figure 6.2 Ladder Logic

Figure 6.3 Example of Ladder Logic

27

PROCESS

P L C

Connectionsto Actuators

Feedback fromSensors/Switches

Figure 6.4 PLC Connection

then power will flow through the output and activate it. Any other combination of input values will result in the output X being off.

6.4.3. PLC CONNECTIONS

When a process is controlled by a PLC it uses input from sensors to make decisions and update outputs to drive actuators, as shown in figure 4. the process is a real process that will change over time. Actuator will drive the system to new states (or modes of operation). This means that the controller is limited by the sensors available, if an input is not available, the controller will have no way to detect a condition.The control loop is a continuous cycle of the PLC reading inputs, solving the ladder logic, and then changing the outputs. Like any computer this does not happen instantly. Figure 4 shows the basic operation cycle of a PLC.

When power is turned on initially the PLC does a quick sanity check to ensure that the hardware is working properly. If there is a problem the PLC will halt and indicate there is an error. For example, if the PLC battery is low and power was lost, the memory will be corrupt and this will result in a fault. If the PLC passes the sanity checks it will then scan (read) all the inputs.

After the input values are stored in memory the ladder logic will be scanned (solved) using the stored values not the current values. This is done to prevent logic problem when inputs change the output will be scanned (the output values will be changed). After this the system goes back to do a sanity check, and the loop continues every scan. Typical times for each of the stages are in the order of milliseconds. 6.4.4. LADDER LOGIC INPUTPLC inputs are easily represented in ladder logic. There are three types of inputs shown.

The first two are normally open and normally closed inputs, discussed previously. The IOT (Immediate Input) function allows input to be read after the input scan, while the ladder logic is being scanned. This allows ladder logic to examine input values .

6.4.5. LADDER LOGIC OUTPUTIIT

Normally Open, an active input X willclose the contact and allow power to

flow

Normally Closed, power flows whenthe input X is not open

Immediate inputs will take currentvalues, not those from the previous

input scan. (NOTE: this instruction isactually an output that will update the

input table with the current input values. Other input contacts can now be

used to examine the new values.)

X

X

X

Figure 6.5 Ladder Logic Input

27

In ladder logic there are multiple type of outputs, but these are not consistently available on all PLC’s. Some of the output will be externally connected to devices outside the PLC, but it is also possible to use internal memory locations in the PLC.Three types of output are shown in figure.

The first is the normal output, when energized the output will turn on, and energize an output. The circle with a diagonal line through is a normally on output. When energized the output will turn off. This type of output is not available on all PLC types. When initially energized the OSR (One Shot Relay) instruction will turn on for one scan, but then be off for all

scans after, until it is turned off. The L (latch) and (unlatch)

instruction can be used to locks output on. When an L output is energized the output will turn on indefinitely, even when the output coil is reenergized. The output can only be turned off using a U output. The last instruction is the IOT (Immediate Output) that will allow outputs to be updated without having to wait for the ladder logic scan to be completed.

6.4.6. COMMUNICATIONS

PLC’s have built in communications ports usually 9-Pin RS232, and optionally for RS485 and Ethernet. Modbus, BACnet or DF1 is usually included as one of the communications protocols. Other options include various field buses such as DeviceNet or Profibus. Other communications protocols that may be used. Most modern PLCs can communicate over a network to some other system, such as a computer running a SCADA (Supervisory Control and Data Acquisition) system or web browser.PLCs used in larger I/O systems may have peer-to-peer (P2P) communication between processors. This allows separate parts of a complex process to have individual control while allowing the subsystems to co-ordinate over the communication link. These communication links are also often used for HMI devices such as keypads or PC-type workstations. Some of today's PLCs can communicate over a wide range of media including RS485, Coaxial, and even Ethernet.

CHAPTER-7

OSR

When power is applied (ON) the

output X is activated for the leftoutput, turned off for the output

An input transition on will causethe output x to go on for one

scan

X

X

X

Figure 6.6 Ladder Logic Output

27

CONCLUSION

It was just like a dream come true for me to pursue training in Aditya Birla Cement ltd. It was really a learning experience for me to have a feel of different Industrial aspects.

In this period I have Learnt those things, which I could not get from books i.e., the practical experience under the guidance of learned professionals.

Special thanks for my college and Aditya Birla Cement Work .

REFRENCE