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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
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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
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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
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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
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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
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LIST OF FIGURES
S.No NAME OF THE FIGURE PAGE NO
2. Schematic diagram of PLC 3
3. Wiring diagram of digital input module
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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
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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.
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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
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PowerSupply
OutputModule
CPU
Program Memory
InputModule
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.
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
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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
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-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
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1 2 3 4 5 6 7 8 9
-24V 10 Fig 2.3 wiring diagram of analog input module
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4 WireTr.
4 WireTr.
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DIGITAL OUTPUT MODULEDOC TB
+24V 1 2 3 4 5
24 V Lamp 6
7 8 9
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1 2 3 4 5 24 V Lamps 6 7 8 9
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-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
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Field
Signals
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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
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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:
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OS
CYCLE
TIME OB PROCESS
ERROR
FC
SFBFCFB
DB
SFCFB
DB
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• 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:
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• 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
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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.
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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:
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Fig4.1 Overall DIP tower control with parameters
4.1 PROCESS:
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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:
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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.
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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.
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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
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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.
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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.
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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.
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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
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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.
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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
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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.
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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
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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
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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
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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.
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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.
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CHAPTER 6
6. OUTPUT:
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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.
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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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