DE-INKING PLANT FINAL TOWER CONTROL USING

SIEMENS PLC

A PROJECT REPORT

Submitted byS.ABDULLAH (611311107002)

T.DEVA SUDAN (611311107301)

S.SAKTHIYUVARAJ (611311107304)

R.SATHISH (611311107305)

In partial fulfillment for the award of the degree

Of

BACHELOR OF ENGINEERING

In

ELECTRONICS AND INSTRUMENTATION ENGINEERING

MAHENDRA ENGINEERING COLLEGE

NAMAKKAL

ANNA UNIVERSITY CHENNAI - 600025

APRIL - 2015

1

ANNA UNIVERSITY CHENNAI - 600025

BONAFIDE CERTIFICATE

It is certified that this project report “DE-INKING PLANT FINAL TOWER

CONTROL USING SIEMENS PLC” is the bonafide work of

“S.ABDULLAH, T.DEVA SUDAN, S.SAKTHIYUVARAJ, R.SATHISH”

who carried out the project work under my supervision.

SIGNATURE SIGNATURE

SUPERVISOR HEAD OF THE DEPARTMENT

Mr. C.R Tamizhanambi, M.E., Mr.S.Senthilkumar,M.E,(Ph.D)Department of Electronics and Department of Electronics and Instrumentation engineering Instrumentation engineering,

Mahendra Engineering College Mahendra Engineering CollegeNamakkal. Namakkal.

Submitted for the viva-voce Examination held on _______________

INTERNAL EXAMINER EXTERNAL EXAMINER

2

TAMILNADU NEWSPRINT PAPER LIMITEDKARUR

BONAFIDE CERTIFICATE

It is certified that this project report “DE-INKING PLANT FINAL TOWER

CONTROL USING SIEMENS PLC” is the bonafide work of

“S.ABDULLAH,T.DEVASUDAN,S.SAKTHIYUVARAJ,R.SATHISH” who

carried out the project work under my supervision.

SIGNATURE

Mr.C.PALANIVEL RAJA, B.E,

Plant Engineer (INST)

TNPL, Karur

3

ABSTRACT

With the emergence of Microcontrollers, associated peripheral

chips and developments in the field of software technology, the whole

scenario related in process of control and automation underwent a

radical change. The Programmable Logic Controllers have in recent

years experienced an unprecedented growth, as a universal element in

industrial automation. The PLC is a solid state device designed to

perform logic functions previously accomplished by

electromechanical relays. Instead of achieving the desired control or

automation through physical wiring of control devices, in PLC it is

achieved through program or software in a PLC. It can be effectively

used in applications, ranging from simple control like replacing small

number of relays, to complex automation problems. With its

tremendous flexibility, real time control, analog value processing, co-

ordination and communication it is used in the automation of many

processes. In this project PLC is implemented in the DIP final tower

control, mainly to speed up the process and to increase the

productivity.

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ACKNOWLEDGEMENT

All praise and glories to the holy name of God, the Lord of all

creations, who by his abundant grace has sustained us and helped us to complete

this project successfully.

In this regard we render our heartfelt thanks to our beloved Principal

Dr. M.MADHESWARAN, M.E., Ph.D., M.B.A., ( Ph.D.),who has given us

the opportunity to carry out this project in this institution.

It is a great pleasure to thank our Head of the Department

Mr.S.SENTHILKUMAR, M.E,( Ph.D)., whose words have proved to be a

great moral support for us in bringing out this project.

Words are inadequate to express our sense of gratitude to our external

guide Mr.R.RAJALINGAM, B.Tech, MBA., Senior Manager of TNPL,

Karur for his invaluable guidance towards this project.

We also thank our internal guide Mr.C.R.TAMIZHANAMBI, M.E.,

who has always been a source of inspiration to us throughout this project.

It’s a great pleasure to thank our Tutor Mr.C.PALANIVEL RAJA, B.E,

Plant Engineer (INST) of TNPL, Karur, who provided the necessary

guidance during the course of this work.

We are grateful to all the Staff members of our department who

offered timely suggestions and advices to bring out this project in time.

Last but not the least we thank our parents and friends, who were

behind us in completing this project a successful one.

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TABLE OF CONTENTS

CHAPTER NO TITLE PAGE NO

ABSTRACT iii

ACKNOWLEDGEMENT iv

LIST OF FIGURES vii

LIST OF ABBREVIATIONS viii

1. GENERAL 1

1.1 INTRODUCTION to PLC 1

1.2 EVOLUTION OF PLC 2

1.3 DISADVANTAGES OF RELAY LOGIC 2

1.4 ADVANTAGES OF PLC 2

2. PLC HARDWARE OVERVIEW 4

2.1 FUNCTIONS OF VARIOUS BLOCKS PLC 4

2.1.1 INPUT MODULE 4

2.1.2 OUTPUT MODULE 5

2.2 CPU 9

2.2.1 ARITHMETIC LOGIC UNIT 9

2.3 POWER SUPPLY 9

2.4 BUS SYSTEM 10

2.5 OPERATION OF PLC 10

6

3. PLC SOFTWARE OVERVIEW 13

3.1 TYPES AND STRUCTURES OF 14

PROGRAMMING BLOCKS

3.2 USER PROGRAM 14

3.3 PROGRAMMING LANGUAGE 19

4. PROCESS DESCRIPTION 21

4.1 PROCESS WITH PROCESS DIAGRAM 23

4.2 ADVANTAGES OF THIS PROJECT 24

OVER EXISTING SYSTEM IN TNPL

5. INSTRUMENT DETAILS 25

5.1 VALVES 25

5.2 TYPES OF VALVES 27

5.3 VALVES USED 33

5.3.1 CONTROL VALVE 33

5.3.2 SOLENOID VALVE 40

5.3.3 ON-OFF VALVE 41

5.4 LEVEL TRANSMITTER AND SENSORS 42

5.5 CONSISTENCY CONTROL 51

6. OUTPUT 53

7. CONCLUSION 59

REFERENCE 60

7

LIST OF FIGURES

S.No NAME OF THE FIGURE PAGE NO

2. Schematic diagram of PLC 3

3. Wiring diagram of digital input module

6

4. Wiring diagram of analog input module 7

5. Wiring diagram of digital output module 8

6. Signal transmission from field to PLC 11

7. Signal processing using program and PIQ 11

8. Signal transmission from PLC to field 12

9. Starting the LAD editor from the SIMATIC manager 13

10. Procedure for creating a logic block in LAD 15

11. Programming procedure for creating data blocks 18

12. Overall DIP tower control with parameters 22

13. Control valve 33

14. Solenoid valve 40

15. ON/OFF valve 41

16. Level Transmitter 42

17. Water level sensor 44

8

CHAPTER 1

1. GENERAL

1.1 Introduction

A Programmable Logic Controller (PLC) is a small, self –contained,

rugged computer designed to control processes and events in an industrial

environment – that is, to take over the job previously done with relay logic

controllers. Wires from switches, sensors and other input devices are attached

directly to PLC. Each PLC contains a microprocessor that has been

programmed to drive the output (O/P). Terminals in specified manner, based on

the signals from the input terminals. The PLC program is usually developed on

the separate programmer (PG) computer such as a Personal Computer (PC),

using special software provided by the PLC manufacturer. Once the program

has been written, it is transferred or downloaded into the PLC.

The basic function of a PLC is to provide output commands to a machine or

process based on some combination of a set of input condition of a set of input

conditions to that machine or process. The PLC is similar to the familiar relay

logic panel but with extended capabilities.

The internal wiring of a PLC is fixed and the logical function that it must

perform are programmed into a “memory”, hence the name “Programmable

Controller”.

The processor with built in routines scan the input signals and in accordance

with the “stored programmed in memory” initiates the required output signals.

The PLC may perform timing, counting and other functions dependent on the

design of the PLC.

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1.2 EVOLUTION OF PLC:

Programmable logic controllers are widely used in automation the

process in any type of industry. Relay logic was used well before the invention

of PLC. A Programmable logic controller is a solid logic control device with a

user programmable memory, which is programmed with a user-oriented

language. So that it can reads input conditions to machine or process.

1.3 DISADVANTAGES OF PLC

• Function is fixed complicated.

• Bulk in size.

• More design time.

• Low response time.

• Up gradation not possible

1.4 ADVANTAGES OF PLC

• Programmable implementing and modification in the logic is very easy. Easy of programming and configuring.

• Reliability.

• Maintainability.

• Fast response time.

• Expandability.

• I/O modules to the external world.

10

CHAPTER 2

2. PLC hardware overview

The PLC is basically a programmed interface between the field-input

element like limit switches, sensor, transducer, push-button etc. and the final

control elements like actuators, solenoid valves, dampers, drives, LED’s, etc.

Programmable controller consists of the following:

1. Input Modules

2. CPU with processor and Program memory

3. Output Modules

4. Bus system

5. Power supply

Field input control

Process

Fig 2.1 Schematic diagram of PLC

11

PowerSupply

OutputModule

CPU

Program Memory

InputModule

.

2.1 Function of Various Blocks in PLC

2.1.1 INPUT MODULE

The input module acts as an interface between the field control inputs

and the CPU.

The Voltage or current signals generated by the sensors, transducers, limit

switches, push buttons etc. are applied to the terminals of the input module.

The input module helps in the following way:

• It converts the field signal into a standard control signal, for

processing by the PLC. The standard control signal delivered by

input module could be 5V or 9V whereas the field signal received

by it could be say 24V DC or 230V AC.

• If required, it isolates the field signal from the CPU.

• It sends one input at a time to CPU by multiplexing action thus

helping in serial communication.

Depending upon the nature of input signal coming from the field, the input

module could be

• Analog Input Module.

• Digital Input Module.

The typical analog current input modules are 4 to 20 mA, 0 to 20 mA and

analog voltage input module are 0 to 500mV and 0 to 10V.

The typical digital input modules are 24V DC, 120V AC and 230V AC.

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2.1.2 OUTPUT MODULE

The output module acts as a link between the CPU and the output devices

located in the field. The field devices could be relay, contractors, lamps,

motorized potentiometers, actuators, solenoid valves, dampers etc. These

devices actually control the process.

The output module converts the output signal delivered by CPU into an

appropriate voltage level suitable for the output field device. The voltage signal

provided by CPU could be 5V or 9V, but the output module converts this

voltage level into say 24V DC, or 120V AC or 230V AC etc.

Thus the output module on receiving signal from the processor, switches

voltage to the respective output terminals. This makes the actuators (i.e.

contractors, relays etc) or indicating lights etc. connected to the terminal, to turn

ON or OFF.

Like input module, an output module could be analog or digital. The

selection is based on the voltage rating of the field output devices. If the output

device is analog then analog output module is required and if its digital like

contractor coil or a lamp then digital output modules have 24V DC, 120V AC,

and 230V AC or relay output.

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DIGITAL INPUT MODULE

DIC TB +24V 1 I 0.0 2 I 0.1 3 I 0.2 4 _______I 0.3 5 I 0.4

6 I 0.5 7 ____ I 0.6 8 9 I 0.7

10

1 I 1.0 2 I 1.1 3 I 1.2 4 I 1.3 5 I 1.4 6 I 1.5 7 I 1.6 8 I 1.7 9

14

-24V

10 Fig2.2 wiring of digital input module

ANOLOG INPUT MODULE AIC TB 230 V 1 - + - + 2 3 4 5 6

7 8 9

10

1 2 3 4 5 6 7 8 9

-24V 10 Fig 2.3 wiring diagram of analog input module

15

4 WireTr.

4 WireTr.

DIGITAL OUTPUT MODULEDOC TB

+24V 1 2 3 4 5

24 V Lamp 6

7 8 9

10

1 2 3 4 5 24 V Lamps 6 7 8 9

16

-24V 10 Fig 2.4 wiring diagram of digital output module

2.2 CENTRAL PROCESSING UNIT

The central Processing Unit or CPU consists of the following blocks.

• Arithmetic Logic Unit (ALU)

• Program memory

• Process image memory (i.e. internal memory of CPU)

• Internal timers and counters

• Flags

The heart of CPU is its microprocessor/micro controller chip.

The working of CPU is fully controlled by the instructions / Program stored in

User Program memory. The user Program directs and controls the CPU’s

working. The user based on the control logic required for the control and

automation task, prepares this Program.

2.2.1 ARITHMETIC LOGIC UNIT (ALU)

ALU is the “organizer” of the PLC.The following operations are carried

out by ALU

• It organizes the input of external signals and data.

• It performs logic operation with the data.

• It performs calculations.

• It takes account of the value of internal timers and counters.

• It takes account of the signal states stored in the flags.

• It stores the signal states of the input in the “Process Output

Image” (internal memory of CPU) during the program scan.

• It organizes the output of the result.

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2.3 POWER SUPPLY

The power supply module generates the voltages required for the

electronic modules of the PLC from the main supply. Typically single phase,

230V AC supply is converted into 24V DC supply by power supply module. It

should be noted that CPU needs 24V DC input, and the CPU generates the other

voltage required by the PLC hardware such as 5V DC etc.

2.4 BUS SYSTEM

Bus system is a path for the transmission of signals. In the programmable

controllers, it is responsible for the signal exchange between processor and

input / output modules. The bus comprises of several signal lines i.e. wires /

tracks.

There are three buses in PLC named,

• Address bus, which enables the selection of memory location or a

module.

• Data bus, which carries the data from modules to processor and vice

versa.

• Control bus, which transfers control and timing signals for the

synchronization of the CPU’s activities within the programmable

controller.

In addition to the above listed modules, the other frequently used modules

in a PLC system are Interface Module, Communication Processor Module and

Function Module or Intelligent Periphery Module.

2.5 OPERATION OF PLC

BRINGING INPUT SIGNAL STATUS TO THE INTERNAL

MEMORY OF CPU

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As discussed earlier, the field signals are connected to input module. At

the output of input module the field status is converted into a voltage level that is

required by the CPU.

At the beginning of each cycle the CPU brings in all the field-input signals

from input module and stores into its internal memory as process image of input

signal. This internal memory of CPU is called as PII (Process Image Input).

The programmable controller operates cyclically i.e. when the program

has been scanned; it starts again at the beginning of the program.

Enable

I/O bus

CPU

CPU

Input

Module

Fig 2.5 signal transmission from field to PLC

PROCESSING OF SIGNALS USING PROGRAM & UPDATING PIQ:

Once the field-input status is brought into the internal memory of CPU

i.e. in PII, the execution of user program, statement-by-statement begins. Based

on the user program the CPU performs logical and arithmetic operation on the

date from PII. It also processes times and counts as well as flag states based on

the instructions.

The results of the user program scan i.e. decision are then stored in the

internal memory of CPU. This internal memory is called Process Image Output

or PIQ Flags

User Program

Memory Internal

Timers

19

Field

Signals

Internal

Counters

Fig 2.6 Signal processing using program and PIQ

SENDING PROCESS OUTPUT IMAGE TO OUTPUT MODULE:

At the end of the program run i.e. at the end of scanning cycle, the CPU

transfers the signal states in the process image output to the output module and

further to field controls.

Enable

Output

CPU module

PII PIQ

Fig 2.7 Signal transmission from PLC to field

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CPU

PII PIQ

FieldOutputDevice

s

CHAPTER 3

3. PLC SOFTWARE OVERVIEW

SIMATIC Manager

The software that is used to program the Siemens S7 PLC is the

SIMATIC MANAGER. It is the basic application for configuring and

programming. The functions performed are

• Set up projects

• Configure and assign parameters to hardware

• Configure hardware networks

• Program blocks

• Debugging and commissioning of programs

Access to the various functions is designed to be object oriented, and

intuitive and easy to learn. The two ways in which the SIMATIC manager can

be worked are,

• Offline ,without a programmable controller connected

• Online, with a programmable controller connected.

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Fig3.1 Starting the LAD editor from the SIMATIC manager

3.1 TYPES AND STRUCTURE OF PROGRAM BLOCKS:

3.1 BLOCKS

The programmable logic controller provides various types of blocks in

which the user program and the related data can be stored. Depending on the

requirements of the process, the program can be structured in different blocks.

3.2 USER PROGRAM

A user program that runs on an S7 CPU is essentially made up of blocks.

It also contains information such as data about the system configuration and

about system networking. Depending on your application, the user program will

include the following elements:

22

OS

CYCLE

TIME OB PROCESS

ERROR

FC

SFBFCFB

DB

SFCFB

DB

• Organization blocks (OBs)

• Function blocks (FBs)

• Functions (FCs)

• Data blocks (DBs)

To simplify your work, you can create your own user-defined data types

(UDTs), which can be used either as data types in their own right or as a

template for creating data blocks. Some of the frequently used blocks such as

the system function blocks (SFBs) and the system functions (SFCs) are

integrated on the CPU. Other blocks (for example blocks for IEC functions or

closed-loop controller blocks) are available as separate packages. You do not

need to program these blocks but simply load them into your user program.

EDITING A LOGIC BLOCK

The order in which you edit the three sections is irrelevant and you can,

of course, make corrections and additions.

When you refer to symbols from the symbol table, you should make sure

that they are complete and, when necessary, add any missing information.

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Fig3.2 Procedure for creating logic blocks in LAD

ORGANISATION BLOCKS

Organization blocks from the interface between the operating system and

the user program. The entire program can be stored in OB1 that is cyclically

called by the operating system (linear program) or it can be divided and stored

in several blocks (structured program).

FUNCTIONS

A function contains a partial functionality of the program. It is possible to

program functions so that they can be assigned parameters.

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As a result functions are also suited for programming recurring, complex

partial functionalities such as calculations. System functions are parameter –

assignable functions integrated in the CPU’s operating system. Both their

number and their functionality are fixed. More information can be found in the

Online Help.

FUNCTION BLOCKS

Basically, function blocks offer the same possibilities as functions in

addition function blocks have their own memory area in the form of instance

data blocks. As a result, function blocks are suited for programming frequently

recurring, complex functionalities such as closed loop control tasks. System

function blocks are parameter assignable functions integrated in the CPU’s

operating system. Both their number and their functionality are fixed. More

information can be found in the Online Help.

DATA BLOCKS

Data blocks are data areas of the user program in which user data are

managed in a structured manner. Data blocks (DBs) are used to handle data

which is why they do not have a code section. A programming data block

involves the following:

• Declaration table: The declaration table is where you specify the data

structure of the data block.

• Block properties: These include extra information such as time stamp,

programming language and path name, which is all entered by the system

itself. You can also add information about the name, family, version and

author and you can assign system attributes for blocks

TYPES OF DATA BLOCKS

A user program can have the following data blocks:

25

• Shared DBs can be accessed by all logic blocks in the program. The data

remains stored in the data block even when it has been closed. If you

require several shared DBs of the same data structure, you can create

them with the help of a UDT. These are data blocks with an associated

user-defined data type.

• Instance DBs are associated with specific function blocks and are

structured according to the declaration table of the FB. You can only

create an instance DB if the corresponding function block exists. They are

data blocks with an associated function block.

Fig3.3 Programming procedure for creating Data blocks

PERMISSIBLE OPERATIONS

26

The use of the entire operation set is possible in all blocks (FC, FB and

OB).

LINEAR PROGRAM

The entire program is found in one continuous program block. This model

resembles a hard-wired relay control that was replaced by a PLC.The CPU

processes the individual instructions one after the other.

PARTITIONED PROGRAM

The program is divided into blocks, whereby every block only contains

the program for solving a partial task. Further partitioning through networks is

possible within a block. The network templates for networks of the same type

can be generated. The organization block OB1 contains instructions that call the

other blocks in a defined sequence.

STRUCTURED PROGRAM

A structured program contains blocks with parameters, so called

parameter assignable blocks. These blocks are designed in such a way that can

be used universally. When a parameter assignable block is called, it is given

current parameters (the exact addresses of inputs and outputs as well as

parameter values)

3.3 PROGRAMMING LANGUAGE

There are several programming languages in STEP 7 that can be used

depending on preference and knowledge. By adhering to specific rules, the

program can be created in statement list and then can be converted into another

programming language.

27

LAD

Ladder diagram is very similar to a circuit diagram .Symbols such as

contacts and coils are used. This programming language appeals to those who

grew up with contactors.

STL

The statement list consists of STEP 7 instructions. The program can be

fairly programmed freely with STL (sometimes to the point of being unable to

follow it anymore). This programming language is preferred by programmers

who are already familiar with other programming languages

FBD

The function block diagram uses “boxes” for the individual functions. The

character in the box indicates the function (e.g.: & indicates AND logic

operation). This programming language has the advantage that even a “non-

programmer” such as a process engineer can work with it.

CYCLIC EXECUTION

So that a newly created block is integrated in the cyclic program execution

of the CPU, it must be called in OB1. The simplest way of inserting the block

call in the graphic programming languages LAD and FBD is through the

browser. In the STL programming language the instruction for calling a block is

CALL. The CALL instruction may be a conditional or unconditional.

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CHAPTER 4

4. PROCESS DESCRIPTION

INTRODUCTION:

The DIP is nothing but de-inking plant (i.e.) removing the ink from the

waste paper and converted into pulp which is stored in the dip final tower. The

dip final tower provides a raw material, which is used for preparing the paper.it

is one of the raw material, which is mixed with the other raw material with

certain proportion to produce the result.

After preparing the raw material in final tower, it should be carried to the

receiving chest of a paper machine. The paper machine is nothing but the area

which consists of serious of segment and portions carried out to manufacture the

paper. The preparation of raw material and transmission of those raw material to

the receiving chest are controlled by certain parameters and function

In our project we are controlling and maintaining those parameters to

produce the fine result.

FINAL TOWER:

The Bulk Amount of Finalized Pulp Is Stored In a Large Tank Known as

Final Tower

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RECEIVING CHEST:

The Stored Pulp from the Final Tower is pumped to the Small Tank (i.e.)

receiving Chest, Where the Pulp Is Transferred to Carry out Serious of Segment

to Manufacture the Paper.

PARAMETERS:

The Parameters to Be Controlled and Maintained Are Level, Flow,

Consistency (Tower Dilutions & Trim Dilution)

PROCESS DIAGRAM:

30

Fig4.1 Overall DIP tower control with parameters

4.1 PROCESS:

31

The de-inking pulp which is started in the final tower can be transmitted

to the Receiving chest, before that the level of the tower is controlled if it is

90% of Level is filled means the pulp transmission gets starts and agitator starts

rotating. If the level is below 10% then the agitator shut off and there is no

Transmission occurs all the valves get closed.

The transmission of pulp first pass through suction valve (on-off valve)

suctioning the pulp gives it to the pumping process (motor), pumps the pulp into

the receiving chest over delivery valve, in case if any consistency of pulp is

varied, pump gets damaged.

Therefore trim dilution control valve is opened, where the water is mixed

with pulp to get operating consistency. Depending on the level of receiving

chest the pumped pulps are controlled by control valves in the input of receiving

chest the same process will be obtained in remaining receiving chest. At last

stored pulp in receiving chest are transmitted to the paper machines.

INTERLOCKS:

For final tower control if the level is 90% means input valve gets closed,

if it is less than 10% means input gets ON. Then the agitator gets starts to rotate

if the level is greater than 5%

Suction valve opened immediately motor gets ON, delivery valve is

opened after 5 seconds. Control valve of receiving chest is controlled, if level is

90% means it gets OFF and less than 10% means gets ON

4.2 ADVANTAGES OVER EXISTING METHOD IN TNPL:

32

In TNPL, it is a newly commissioning plant, now the plant is prepared

with the DCS control system, so that interlocks between the control components

are high and the cost of the components used in the control system are also high,

for that we are introducing the programmable logic controller (PLC) to the

control system.

By using PLC we are acquiring so many benefits including the interlocks

which is quietly reduced and the cost also gets reduced, with a PLC system we

are controlling less number of inputs and outputs, which is more than enough

for our project and the scan time of a system gets reduced which improves the

speed of the control system, by improving the speed of a system ,the production

of raw material for preparing the paper in DIP also gets increased (i.e.)the

production gets increased 40% more than the existing output in TNPL, so that

profit acquired by introducing our project gets increased by 1/4th of the existing

income.

33

CHAPTER 5 5.INSTRUMENT DETAILS

5.1 VALVE

A valve is a device that regulates, directs or controls the flow of a fluid

(gases, liquids, fluidized solids, or slurries) by opening, closing, or partially

obstructing various passageways. Valves are technically valves fittings, but are

usually discussed as a separate category. In an open valve, fluid flows in a

direction from higher pressure to lower pressure.

The simplest, and very ancient, valve is simply a freely hinged flap which

drops to obstruct fluid (gas or liquid) flow in one direction, but is pushed open

by flow in the opposite direction. This is called a check valve, as it prevents or

"checks" the flow in one direction.

Valves have many uses, including controlling water for Irrigation,

industrial uses for controlling processes, residential uses such as on / off &

pressure control to dish and clothes washers & taps in the home. Even aerosols

have a tiny valve built in. Valves are also used in the military & transport

sectors.

34

Valves are found in virtually every industrial process, including water &

sewage processing, mining, power generation, processing of oil, gas &

petroleum, food manufacturing, chemical & plastic manufacturing and many

other fields.

In developed nations we use valves in our daily lives; the most noticeable

are plumbing valves, such as taps for tap water. Other familiar examples include

gas control valves on cookers, small valves fitted to washing

machines and dishwashers, safety devices fitted to hot water systems,

and poppet valves in car engines.

Valve is not only a flow controlling device; It also regulates the flow,

regulates and controls the pressure. 1. Ball valve 2.Butterfly valve 3.Gate valve

4.Globe valve 5.Needle valve

35

In nature there can be found examples of valves, for example veins

acting as valves are controlling the blood circulation & heart valves control the

flow of blood in the chambers of the heart and maintain the correct pumping

action.

Valves may be operated manually, either by a handle, lever, pedal or

wheel. Valves may also be automatic, driven by changes

in pressure, temperature, or flow. These changes may act upon a diaphragm or

a piston which in turn activates the valve, examples of this type of valve found

commonly are safety valves fitted to hot water systems or boilers.

More complex control systems using valves requiring automatic control

based on an external input (i.e., regulating flow through a pipe to a changing set

point) require an actuator. An actuator will stroke the valve depending on its

input and set-up, allowing the valve to be positioned accurately, and allowing

control over a variety of requirements.

5.2 TYPES OF VALVE

BALL VALVE

A ball valve is a valve with a spherical disc, the part of the valve which

controls the flow through it. The sphere has a hole, or port, through the middle

so that when the port is in line with both ends of the valve, flow will occur.

When the valve is closed, the hole is perpendicular to the ends of the valve, and

flow is blocked. The handle or lever will be in line with the port position letting

you "see" the valve's position. The ball valve, along with the butterfly

valve and plug valve, are part of the family of quarter turn valves.

36

Ball valves are durable and usually work to achieve perfect shutoff even

after years of disuse. They are therefore an excellent choice for shutoff

applications (and are often preferred to globe valves and gate valves for this

purpose). They do not offer the fine control that may be necessary in throttling

applications but are sometimes used for this purpose.

BUTTERFLY VALVE

A butterfly valve is a valve which can be used for isolating or

regulating flow. The closing mechanism takes the form of a disk. Operation is

similar to that of a ball valve, which allows for quick shut off. Butterfly valves

are generally favored because they are lower in cost to other valve designs as

well as being lighter in weight, meaning less support is required.

The disc is positioned in the center of the pipe, passing through the disc is

a rod connected to an actuator on the outside of the valve.

Rotating the actuator turns the disc either parallel or perpendicular to the

flow. Unlike a ball valve, the disc is always present within the flow; therefore

a pressure drop is always induced in the flow, regardless of valve position.

37

A butterfly valve is from a family of valves called quarter-turn valves.

The "butterfly" is a metal disc mounted on a rod. When the valve is closed, the

disc is turned so that it completely blocks off the passageway. When the valve is

fully open, the disc is rotated a quarter turn so that it allows an almost

unrestricted passage of the fluid. The valve may also be opened incrementally

to throttle flow.

There are different kinds of butterfly valves, each adapted for different

pressures and different usage. The resilient butterfly valve, which uses the

flexibility of rubber, has the lowest pressure rating. The high performance

butterfly valve, used in slightly higher-pressure systems, features a slight offset

in the way the disc is positioned, which increases the valve's sealing ability and

decreases its tendency to wear.

The valve best suited for high-pressure systems is the triple offset

butterfly valve, which makes use of a metal seat and is therefore able to

withstand a greater amount of pressure

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GLOBE VALVE

A globe valve different from ball valve is a type of valve used for

regulating flow in a pipeline, consisting of a movable disk-type element and a

stationary ring seat in a generally spherical body.

Globe valves are named for their spherical body shape with the two

halves of the body being separated by an internal baffle. This has an opening

that forms a seat onto which a movable plug can be screwed in to close (or shut)

the valve.

GATE VALVE

The gate valve, also known as a sluice valve, is a valve that opens by

lifting a round or rectangular gate/wedge out of the path of the fluid. The

distinct feature of a gate valve is the sealing surfaces between the gate and seats

are planar, so gate valves are often used when a straight-line flow of fluid and

minimum restriction is desired. The gate faces can form a wedge shape or they

can be parallel.

39

Gate valves are primarily used to permit or prevent the flow of liquids,

but typical gate valves shouldn't be used for regulating flow, unless they are

specifically designed for that purpose. Because of their ability to cut through

liquids, gate valves are often used in the petroleum industry.

For extremely thick fluids, a specialty valve often known as a knife

valve is used to cut through the liquid. On opening the gate valve, the flow path

is enlarged in a highly nonlinear manner with respect to percent of opening.

This means that flow rate does not change evenly with stem travel.

Also, a partially open gate disk tends to vibrate from the fluid flow. Most

of the flow change occurs near shutoff with a relatively high fluid velocity

causing disk and seat wear and eventual leakage if used to regulate flow.

Typical gate valves are designed to be fully opened or closed. When fully open,

the typical gate valve has no obstruction in the flow path, resulting in very

low friction loss.

NEEDLE VALVE

Needle valves may also be used in vacuum systems, when a precise

control of gas flow is required, at low pressure, such as when filling gas-filled

vacuum tubes, gas lasers and similar devices. The virtue of the needle valve is

40

from the vernier effect of the ratio between the needle's length and its diameter,

or the difference in diameter between needle and seat. A long travel axially (the

control input) makes for a very small and precise change radically (affecting the

resultant flow).

A needle valve has a relatively small orifice with a long, tapered seat, and

a needle-shaped plunger, on the end of a screw, which exactly fits this seat.

As the screw is turned and the plunger retracted, flow between the seat

and the plunger is possible; however, until the plunger is completely retracted

the fluid flow is significantly impeded. Since it takes many turns of the fine-

threaded screw to retract the plunger, precise regulation of the flow rate is

possible.

USES

Needle valves are usually used in flow metering applications, especially

when a constant, calibrated, low flow rate must be maintained for some time,

such as the idle fuel flow in a carburetor. Small, simple needle valves are often

used as bleed valves in hot water heating applications.

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5.3 VALVES USED

5.3.1 CONTROL VALVES

Fig 5.1 Control valve

Control valves are valves used to control conditions such

as flow, pressure, temperature, and liquid level by fully or partially opening or

closing in response to signals received from controllers that compare a "set

point" to a "process variable" whose value is provided by sensors that monitor

changes in such conditions.

The opening or closing of control valves is usually done automatically

by electrical, hydraulic or pneumatic actuators. Positioners are used to control

the opening or closing of the actuator based on electric or pneumatic signals.

These control signals, traditionally based on 3-15psi (0.2-1.0bar), more

common now are 4-20mA signals for industry, 0-10V for HVAC systems, and

the introduction of "Smart" systems, HART, Field bus Foundation,

and Profibus being the more common protocols.

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A control valve consists of three main parts in which each part exist in

several types and designs:

• Valve's actuator

• Valve's positioner

• Valve's body

A flow control valve regulates the flow or pressure of a fluid. Control valves

normally respond to signals generated by independent devices such as flow

meters or temperature gauges.

Control valves are normally fitted with actuators and

positioners. Pneumatically-actuated globe valves and Diaphragm Valves are

widely used for control purposes in many industries, although quarter-turn types

such as (modified) ball, gate and butterfly valves are also used.

Control valves can also work with hydraulic actuators (also known as

hydraulic pilots). These types of valves are also known as Automatic Control

Valves. The hydraulic actuators will respond to changes of pressure or flow and

will open/close the valve. Automatic Control Valves do not require an external

power source, meaning that the fluid pressure is enough to open and close the

valve. Automatic control valves include: pressure reducing valves, flow control

valves, back-pressure sustaining valves, altitude valves, and relief valves. An

altitude valve controls the level of a tank.

The altitude valve will remain open while the tank is not full and it will close

when the tanks reaches its maximum level. The opening and closing of the

valve requires no external power source (electric, pneumatic, or man power), it

is done automatically, hence its name.

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Process plants consist of hundreds, or even thousands, of control loops all

networked together to produce a product to be offered for sale. Each of these

control loops is designed to keep some important process variable such as

pressure, flow, level, temperature, etc. within a required operating range to

ensure the quality of the end product. Each of these loops receives and

internally creates disturbances that detrimentally affect the process variable, and

interaction from other loops in the network provides disturbances that influence

the process variable.

To reduce the effect of these load disturbances, sensors and transmitters

collect information about the process variable and its relationship to some

desired set point. A controller then processes this information and decides what

must be done to get the process variable back to where it should be after a load

disturbance occurs. When all the measuring, comparing, and calculating are

done, some type of final control element must implement the strategy selected

by the controller.

The most common final control element in the process control industries is

the control valve. The control valve manipulates a flowing fluid, such as gas,

steam, water, or chemical compounds, to compensate for the load disturbance

and keep the regulated process variable as close as possible to the desired set

point.

INHERENT CONTROL VALVE FLOW CHARACTERISTICS

The most common characteristics are shown in the figure above. The percent

of flow through the valve is plotted against valve stem position. The curves

shown are typical of those available from valve manufacturers. These curves are

based on constant pressure drop across the valve and are called inherent flow

characteristics.

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• Linear - flow capacity increases linearly with valve travel.

• Equal percentage - flow capacity increases exponentially with valve

trim travel. Equal increments of valve travel produce equal percentage

changes in the existing Cv.

• A modified parabolic characteristic is approximately midway between

linear and equal-percentage characteristics. It provides fine throttling at

low flow capacity and approximately linear characteristics at higher flow

capacity.

• Quick opening provides large changes in flow for very small changes in

lift. It usually has too high a valve gain for use in modulating control. So

it is limited to on-off service, such as sequential operation in either batch

or semi-continuous processes.

• Hyperbolic

• Square Root

The majority of control applications are valves with linear, equal-

percentage, or modified-flow characteristics.

INSTALLED CONTROL VALVE FLOW CHARACTERISTICS

When valves are installed with pumps, piping and fittings, and other process

equipment, the pressure drop across the valve will vary as the plug moves

through its travel.

When the actual flow in a system is plotted against valve opening, the curve

is called the Installed Flow Characteristic.

In most applications, when the valve opens, and the resistance due to fluids

flow decreases the pressure drop across the valve. This moves the inherent

characteristic:

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• A linear inherent curve will in general resemble a quick opening

characteristic

• An equal percentage curve will in general resemble a linear curve

CAVITATION

If the speed through the valve is high enough, the pressure in the liquid

may drop to a level where the fluid may start bubble or flash. The pressure

recovers sufficiently and the bubbles collapse upon themselves.

Cavitation may be noisy but is usually of low intensity and low frequency. This

situation is extremely destructive and may wear out the trim and body parts of

the valve in short time.

46

APPLICATION RATIO

A common way to characterize potential cavitation conditions is the

"applications ratio" (or "the incipient cavitation index") and can be expressed as

AR = pi - po / (pi - pv) (1)

where

AR = Application Ratio

pi = inlet pressure, absolute

po = outlet pressure, absolute

pv = vapor pressure of the fluid, absolute

For application ratios above 1 - the fluid flashes. This is not the same as

cavitation, but the closer the ratio is to 1, the higher the potential for cavitation.

NOTE: With an increasing fluid temperature the possibility

for cavitation increases.

Example - Flashing Water

If we know the boiling point and the absolute pressure of a fluid (Steam Table

with saturated steam properties) the minimum outlet pressure from a valve to

avoid flashing can be calculated.

For an application ratio of one, equation (1) can modified to

AR = 1

= pi - po / (pi - pv)

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or transformed

po = pv

Using "Steam Table" with saturated steam properties we can conclude that

• for a water temperature of 17.51 oC and absolute inlet pressure of 1 bar -

the minimum outlet pressure is 0.02 bar to avoid flashing

• for a water temperature of 81.35 oC and absolute inlet pressure of 1 bar -

the minimum outlet pressure is 0.5 bar to avoid flashing

• For a water temperature of 99.63 oC and absolute inlet pressure of 1 bar -

the minimum outlet pressure is 1 bar to avoid flashing

NOTE: Flashing is not the same as cavitation. Due to local conditions in a

valve cavitation may start on much higher outlet pressures.

MULTISTAGE CONTROL VALVES

Cavitation can be avoided by using more than one control valve or more

convenient - a multistage control valve.

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As illustrated above the "vena contracta" is much lower for a single stage

valve than a multi stage valve. Depending on the pressure drop and the

temperature of the fluid its possible to avoid cavitation conditions using more

than one stage in a valve.

RELATIONSHIP BETWEEN CONTROL VALVE CAPACITY AND

VALVE STEAM

The relationship between control valve capacity and valve stem travel is

known as the Flow Characteristic of the Control Valve

Trim design of the valve affects how the control valve capacity changes

as the valve moves through its complete travel. Because of the variation in trim

design, many valves are not linear in nature. Valve trims are instead designed,

or characterized, in order to meet the large variety of control application needs.

Many control loops have inherent non linearity's, which may be possible to

compensate selecting the control valve trim.

5.3.2 SOLENOID VALVE

Fig5.2 solenoid valve

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Port 3 and 5 Exhaust Port

Port 1 Input Port

Port 4 and 2 Output Port

When the voltage supply is given to the solenoid coil, the solenoid is

energized and the port changing occurs (i.e.) under no supply to the solenoid

coil, the output port 2 is active, and under supply to solenoid coil the output port

4 is active.

A manual override is used to change the port manual without supply to

the solenoid coil. An LED glows when the supply is given to the solenoid coil.

5.3.3 ON-OFF VALVE

Fig 5.3 ON/OFF valve

In our project we have used butterfly valve as ON-OFF valve. The double

acting piston actuator is used to ON-OFF the butterfly valve. When the air

supplied to port 2, forces the pistons apart and towards end positions with

exhaust air existing at port 4(a counter clockwise rotation is obtained).When the

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air is supplied to port 4, it forces pistons towards center with exhaust air

existing at port 2(a clockwise rotation is obtained).

1- Port2

2- port4

5.4 LEVEL TRANSMITTER

Fig 5.4 Level Transmitter

Level transmitter is used to measure the level of the tank, and convert into

4-20mA signal that is accepted by the PLC. The level transmitter is mounted in

the bottom of tank as shown in the figure (5.4). The level in the tank is

calculated by finding the differential pressure in the tank

∆P=P1-P2

P1=Total Pressure in the tank

P2=Atmospheric Pressure

By knowing the density of the liquid, level (height) of the tank is found out

H=∆P/ρg

H - Height of the liquid level in the tank.

∆p – Differential pressure.

ρ - Density of the liquid.

The level transmitters consist of ceramic sensor as sensing element. The

ceramic sensor consists of a substrate and two diaphragms. The diaphragms and

51

substrate constitute two measuring surfaces and are connected by capillary,

silicon oil, mineral oil or inert oil serves as filling fluid.

A differential pressure proportional change in the capacitance is measured

by electrode on the capacitance is measured by electrode on the ceramic

soubrette and diaphragms. The change on capacitance is converted into 4-

20mA output by the electronic circuit board in the transmitter.

LEVEL SENSOR

Level sensors detect the level of substances that flow,

including liquids, slurries, granular materials, and powders. Fluids and fluidized

solids flow to become essentially level in their containers (or other physical

boundaries) because of gravity whereas most bulk solids pile at an angle of

repose to a peak. The substance to be measured can be inside a container or can

be in its natural form (e.g., a river or a lake). The level measurement can be

either continuous or point values.

Continuous level sensors measure level within a specified range and

determine the exact amount of substance in a certain place, while point-level

sensors only indicate whether the substance is above or below the sensing point.

Generally the latter detect levels that are excessively high or low.

There are many physical and application variables that affect the selection

of the optimal level monitoring method for industrial and commercial processes.

The selection criteria include the physical: phase (liquid, solid or

slurry), temperature, pressure or vacuum, chemistry, dielectric

constant of medium, density (specific gravity) of medium, agitation (action),

acoustical or electrical noise, vibration, mechanical shock, tank or bin size and

shape. Also important are the application constraints: price, accuracy,

appearance, response rate, ease of calibration or programming, physical size and

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mounting of the instrument, monitoring or control of continuous or discrete

(point) levels.

WATER LEVEL SENSOR

Fig 5.5 Water level sensor

POINT LEVEL DETECTION OF LIQUIDS:

MAGNETIC AND MECHANICAL FLOAT

The principle behind magnetic, mechanical, cable, and other float level

sensors involves the opening or closing of a mechanical switch, either through

direct contact with the switch, or magnetic operation of a reed. With

magnetically actuated float sensors, switching occurs when a permanent magnet

sealed inside a float rises or falls to the actuation level. With a mechanically

actuated float, switching occurs as a result of the movement of a float against a

miniature (micro) switch. For both magnetic and mechanical float level sensors,

chemical compatibility, temperature, specific gravity (density), buoyancy, and

viscosity affect the selection of the stem and the float.

For example, larger floats may be used with liquids with specific

gravities as low as 0.5 while still maintaining buoyancy. The choice of float

material is also influenced by temperature-induced changes in specific gravity

and viscosity – changes that directly affect buoyancy.

53

Float-type sensors can be designed so that a shield protects the float itself

from turbulence and wave motion. Float sensors operate well in a wide variety

of liquids, including corrosives. When used for organic solvents, however, one

will need to verify that these liquids are chemically compatible with the

materials used to construct the sensor. Float-style sensors should not be used

with high viscosity (thick) liquids, sludge or liquids that adhere to the stem or

floats, or materials that contain contaminants such as metal chips; other sensing

technologies are better suited for these applications.

A special application of float type sensors is the determination of

interface level in oil-water separation systems. Two floats can be used with each

float sized to match the specific gravity of the oil on one hand, and the water on

the other. Another special application of a stem type float switch is the

installation of temperature or pressure sensors to create a multi-parameter

sensor. Magnetic float switches are popular for simplicity, dependability and

low cost.

PNEUMATIC

Pneumatic level sensors are used where hazardous conditions exist, where

there is no electric power or its use is restricted, and in applications involving

heavy sludge or slurry. As the compression of a column of air against a

diaphragm is used to actuate a switch, no process liquid contacts the

sensor's moving parts. These sensors are suitable for use with highly viscous

liquids such as grease, as well as water-based and corrosive liquids. This has the

additional benefit of being a relatively low cost technique for point level

monitoring.

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CONDUCTIVE

Conductive level sensors are ideal for the point level detection of a wide

range of conductive liquids such as water, and is especially well suited for

highly corrosive liquids such as caustic soda, hydrochloric acid, nitric acid,

ferric chloride, and similar liquids.

For those conductive liquids that are corrosive, the sensor’s electrodes

need to be constructed from titanium, Hastelloy B or C, or 316 stainless steel

and insulated with spacers, separators or holders of ceramic, polyethylene and

Teflon-based materials.

Depending on their design, multiple electrodes of differing lengths can be

used with one holder. Since corrosive liquids become more aggressive as

temperature and pressure increase, these extreme conditions need to be

considered when specifying these sensors.

Conductive level sensors use a low-voltage, current-limited power source

applied across separate electrodes. The power supply is matched to the

conductivity of the liquid, with higher voltage versions designed to operate in

less conductive (higher resistance) mediums. The power source frequently

incorporates some aspect of control, such as high-low or alternating pump

control. A conductive liquid contacting both the longest probe (common) and a

shorter probe (return) completes a conductive circuit.

Conductive sensors are extremely safe because they use low voltages and

currents. Since the current and voltage used is inherently small, for personal

safety reasons, the technique is also capable of being made “Intrinsically Safe”

to meet international standards for hazardous locations.

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Conductive probes have the additional benefit of being solid-state devices

and are very simple to install and use. In some liquids and applications,

maintenance can be an issue. The probe must continue to be conductive.

If buildup insulates the probe from the medium, it will stop working

properly. A simple inspection of the probe will require an ohmmeter connected

across the suspect probe and the ground reference.

Typically, in most water and wastewater wells, the well itself with its

ladders, pumps and other metal installations, provides a ground return.

However, in chemical tanks, and other non-grounded wells, the installer must

supply a ground return, typically an earth rod.

SENSORS FOR CONTINUOS MONITORING

ULTRASONIC

Ultrasonic level sensors are used for non-contact level sensing of highly

viscous liquids, as well as bulk solids. They are also widely used in water

treatment applications for pump control and open channel flow measurement.

The sensors emit high frequency (20 kHz to 200 kHz) acoustic waves that are

reflected back to and detected by the emitting transducer.

Ultrasonic level sensors are also affected by the changing speed of

sound due to moisture, temperature, and pressures. Correction factors can be

applied to the level measurement to improve the accuracy of measurement.

Turbulence, foam, steam, chemical mists (vapors), and changes in the

concentration of the process material also affect the ultrasonic sensor’s

response. Turbulence and foam prevent the sound wave from being properly

reflected to the sensor; steam and chemical mists and vapors distort or absorb

the sound wave; and variations in concentration cause changes in the amount of

56

energy in the sound wave that is reflected back to the sensor. Stilling wells and

wave guides are used to prevent errors caused by these factors.

Proper mounting of the transducer is required to ensure best response to

reflected sound. In addition, the hopper, bin, or tank should be relatively free of

obstacles such as weldments, brackets, or ladders to minimize false returns and

the resulting erroneous response, although most modern systems have

sufficiently "intelligent" echo processing to make engineering changes largely

unnecessary except where an intrusion blocks the "line of sight" of the

transducer to the target.

Since the ultrasonic transducer is used both for transmitting and receiving

the acoustic energy, it is subject to a period of mechanical vibration known as

“ringing”. This vibration must attenuate (stop) before the echoed signal can be

processed.

The net result is a distance from the face of the transducer that is blind

and cannot detect an object. It is known as the “blanking zone”, typically

150mm – 1m, depending on the range of the transducer.

The requirement for electronic signal processing circuitry can be used to

make the ultrasonic sensor an intelligent device. Ultrasonic sensors can be

designed to provide point level control, continuous monitoring or both. Due to

the presence of a microprocessor and relatively low power consumption, there is

also capability for serial communication from to other computing devices

making this a good technique for adjusting calibration and filtering of the sensor

signal, remote wireless monitoring or plant network communications. The

ultrasonic sensor enjoys wide popularity due to the powerful mix of low price

and high functionality.

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CAPACITANCE

Capacitance level sensors excel in sensing the presence of a wide variety

of solids, aqueous and organic liquids, and slurries. The technique is frequently

referred to as RF for the radio frequency signals applied to the capacitance

circuit. The sensors can be designed to sense material with dielectric

constants as low as 1.1 (coke and fly ash) and as high as 88 (water) or more.

Sludge and slurries such as dehydrated cake and sewage slurry (dielectric

constant approx. 50) and liquid chemicals such as quicklime (dielectric constant

approx. 90) can also be sensed. Dual-probe capacitance level sensors can also

be used to sense the interface between two immiscible liquids with substantially

different dielectric constants, providing a solid state alternative to the

aforementioned magnetic float switch for the “oil-water interface” application.

Since capacitance level sensors are electronic devices, phase modulation

and the use of higher frequencies makes the sensor suitable for applications in

which dielectric constants are similar. The sensor contains no moving parts, is

rugged, simple to use, and easy to clean, and can be designed for high

temperature and pressure applications. A danger exists from build-up and

discharge of a high-voltage static charge that results from the rubbing and

58

movement of low dielectric materials, but this danger can be eliminated with

proper design and grounding.

Appropriate choice of probe materials reduces or eliminates problems

caused by abrasion and corrosion. Point level sensing of adhesives and high-

viscosity materials such as oil and grease can result in the build-up of material

on the probe; however, this can be minimized by using a self-tuning sensor. For

liquids prone to foaming and applications prone to splashing or turbulence,

capacitance level sensors can be designed with splashguards or stilling wells,

among other devices.

A significant limitation for capacitance probes is in tall bins used for

storing bulk solids. The requirement for a conductive probe that extends to the

bottom of the measured range is problematic. Long conductive cable probes (20

to 50 meters long), suspended into the bin or silo, are subject to tremendous

mechanical tension due to the weight of the bulk powder in the silo and the

friction applied to the cable. Such installations will frequently result in a cable

breakage.

OPTICAL INTERFACE

Optical sensors are used for point level sensing of sediments, liquids with

suspended solids, and liquid-liquid interfaces. These sensors sense the decrease

or change in transmission of infrared light emitted from an infrared diode

(LED). With the proper choice of construction materials and mounting location,

these sensors can be used with aqueous, organic, and corrosive liquids.

A common application of economical infrared-based optical interface

point level sensors is detecting the sludge/water interface in settling ponds. By

using pulse modulation techniques and a high power infrared diode, one can

59

eliminate interference from ambient light, operate the LED at a higher gain, and

lessen the effects of build-up on the probe.

An alternate approach for continuous optical level sensing involves the

use of a laser. Laser light is more concentrated and therefore is more capable of

penetrating dusty or steamy environments. Laser light will reflect off most

solid, liquid surfaces. The time of flight can be measured with precise timing

circuitry, to determine the range or distance of the surface from the sensor.

Lasers remain limited in use in industrial applications due to cost, and concern

for maintenance. The optics must be frequently cleaned to maintain

performance.

5.5 CONSISTENCY CONTROL

Consistency control is one of the most important and yet common

controls in the wet end of a paper machine. Nevertheless, it is at the same time

one of the most poorly implemented loops on many paper machines.

In this presentation, the several different process objectives with

appropriate control strategies will be considered.

These strategies take into consideration varying production demand,

varying dilution line pressure, limited measurement capabilities and varying

stock properties. What will be shown is that although there is no single ideal

strategy, that at times the simple two element strategy is best, but, at other

times, that dilution flow ratio, proportional only dilution flow, recirculation or

adaptive gain controls are better choices.

The control of consistency is a very large topic to cover well in a short paper.

Our focus will be from theperspective of process control, specifically looking at

the strategies that one can use to perform low variability consistency control.

60

The EnTech Control Performance Group of Emerson Process

Management encourages a scientific and methodical approach to process and

control design, control tuning and process troubleshooting.

In taking that approach, this paper will address the following:

● What are the Process Objectives and constraints for the most common

consistency processes?

● What are the potential impediments to achieving those objectives?

● What are the Control Strategy Objectives that will help to achieve the Process

Objectives?

● For the most common forms of consistency processes, what are the most

appropriate strategies?

Like physicists, many control engineers would like to find one strategy

that will solve all control problems (The Unified Field Theory for control

engineering). Unlike Physicists, Control Engineers are expected to be practical.

So the key thesis of this paper is that there is no single strategy for

consistency control that satisfies all requirements.

However, using a scientific and methodical approach to the problem, one

can make significant improvements to the various consistency processes in a

mill by choosing the most appropriate strategies for them.

61

CHAPTER 6

6. OUTPUT:

62

63

64

65

66

CHAPTER 7

7. CONCLUSION:

In Tamilnadu News Print And Papers Limited this project is

implemented to increase the productivity. With the automation for all

operations in paper manufacturing, this DIP final tower control using PLC

made it very comfort to increase production and to achieve goals. In future this

system can be updated for more tanks with the same program. And it may

be possible to implement using the same PLC or distributed control systems.

67

REFERENCES

1. Programmable logic controllers, by (W.Bolton).

2. Programmable logic controllers by Raymond Vandeerbok.

3. PLC: Automation with programmable logic controllers by Peter

Rohner.

4. Intro to PLC by Gary Dunning.

5. Automating of BOSCH transfer system TS1 by SIEMENS PLC S7-

300: final project work by Pierre - Olivier Tarralo.

6. Control valve primer by H.D. Baumann.

7. Control valve selection and sizing by ,Les Drieskell.

8. ISA handbook of control valves, by James W.Hutchison, Instrument

Society of America.

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