modeling an enhanced e- voting system
TRANSCRIPT
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MODELING AN ENHANCED E-VOTING SYSTEM WITH REALTIME DATA COLLATION
BY
EGUONO, EGUONO E.
2009112000
A PROJECT REPORT SUBMITTED TO THE DEPARTMENT OFELECTRICAL/ELECTRONICS ENGINEERING,
ANAMBRA STATE UNIVERSITY OF SCIENCE ANDTECHNOLOGY, ULI
IN PARTIAL FULFILLMENT OF THE REQUIREMENT FORTHE AWARD OF MASTERS DEGREE IN ELECTRICAL
ENGINEERING
SUPERVISOR
DR. P.I. OKWU
DECEMBER, 2013
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DECLARATION
I hereby declare that this report was written by me and it is a
record of my own research. It has not been presented before in
any previous application for a Masters Degree. Authors whose
works have been referred to and reference made to published
literature have been duly acknowledged.
_________________________ ___________________
EGUONO, EGUONO EGUONO Date
Student
Above declaration is confirmed
____________________ _____________________
DR.P.I. OKWU Date
Project Supervisor
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CERTIFICATION
This project titled: MODELING AN ENHANCED E-VOTINGSYSTEM WITH REAL TIME DATA COLLATION BY EGUONOEGUONO EGUONO meets the regulations governing the awardof Masters Degree in Electrical Engineering at Anambra StateUniversity of Science and Technology, Uli and is approved forits contribution to knowledge and literature presentation.
________________________ ____________________DR. P.I. OKWU DateProject supervisor
_____________________ _____________________PROF. S.S.S. OKEKE DateHead of Department
_____________________ ___________________External Examiner Date
This is to certify that the thesis has been examined and
approved for the award of the degree of masters in
Telecommunication Engineering (M.Eng).
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_____________________ ___________________External Examiner Date
_____________________ _____________________Supervisor Date
_____________________ ___________________Head of Department Date
_____________________ _____________________Dean of Faculty of DateEngineering
_____________________ ___________________Dean of School of DatePostgraduate Studies
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DEDICATION
This project report is dedicated to the Almighty God, whose
boundless mercies and love has made this research project a
huge success.
ACKNOWLEDGEMENTS
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I will always owe my unreserved gratitude to my lecturers: Dr.
P.I. Okwu my Project Supervisor, and Programme Coordinator
who worked relentlessly to make me what I have become
today, and for his readiness to help at all time, despite tight
schedules; Mal. Sanni Abdullahi, my HOD, for his painstaking
efforts towards making the Department one of the best. Special
thanks to Engr. Toyin Taiwo, Abebayo B. Michael, and Ishaya
Hope Joshua for their kind support throughout the period of this
Programme.
I must not forget my mother: Mrs. Eunice Anagwu, and Lady,
Florence Ulasi, whose love and belief in me always soured me
to go for higher achievements. I will not forget my brothers ad
sisters: Joy, Ngozi Anagwu, Mr. and Mrs. Chinedu Anagwu, Mr.
and Mrs. Felix Chikodi Reginald, Mr. and Mrs. Chuwkunonso
Anagwu, Pharm, & Mrs. Chimezie Anagwu, Okwudili, Nnamdi,
your prayers have really been fruitful.
To my friends and colleagues: Obinna Obi, Ikechukwu Igboebisi,
Kelechi Mbagwu, Ya u, Mrs. Gloria Ndubueze and others whose
name I may not be able to mention, know that your memories
shall always remain with me.
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TABLE OF CONTENT
Title . . . . . . . . . i
Declaration . . . . . . . . ii
Certification . . . . . . . .
iii
Acknowledgement . . . . . . .
iv
Dedication . . . . . . . . v
Table of Contents . . . . . . .
Vi-viii
List of Figures . . . . . . . .
ix
List of Tables . . . . . . . .
x
Abstract . . . . . . . . .
xi
CHAPTER ONE: INTRODUCTION
1.1 Project Background . . . . . .
1
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1.2 Aims of Objectives . . . . . .
4
1.3 Significance of the Study . . . . .
5
1.4 Scope of the Work . . . . . .
11
1.5 Block Diagram overview of the Project stages
13
1.6 Project Report Organization . . . .
15
CHAPTER TWO: REVIEW OF RELATED LITERATURES
2.1 Review of work on temperature controllers .. . 17
2.1.1Principle of Operation . . . . 17
2.1.2Technologies available . . . . .
19
2.1.3 New Trends . . . . . . .
22
2.2 Set-up overview . . . . . . 25
2.2.1Temperature Measurement and Sensors . . .
25
2.2.2Microcontroller . . . . . . 32
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2.2.3 Serial Communication RS 232 Technology .
33
CHAPTER THREE: METHODOLOGY AND SYSTEM ANALYSIS
3.1 Methodology. . . . . . .
37
3.1.1Structured Analysis and Design method .. .. ..
.. 37
3.1.2Top-Down Design . . . . . .
41
3.1.3 Bottom Up Design . . . . . .
42
3.1.4 Choice Design Approach . . . . .
42
3.2 Limitations of the existing system .. . .
43
CHAPTER FOUR: SYSTEM DESIGN
4.1 System Specification . . . . . 45
4.2 Hardware Subsystem design . . . .
46
4.2.1Input interface . . . . . . 46
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4.2.2 The Control System design . . . .
51
4.2.3 Interfacing relay drivers to the microcontroller
output port . 55
4.3 Software Subsystem design . . . .
61
4.3.1Program block diagram and Control Algorithm .
61
4.3.2 Configuring the serial port of the microcontroller
63
4.3.3 Configuring the PC serial port . . . .
66
4.4 The input/output arrangement of the Project
68
4.5 The Project Block Diagram . .
69
5.1 Hardware Subsystem Implementation .
70
5.1.1The Input Interface Implementation . 70
5.1.2The Control System Implementation .
72
5.1.3. The Output Interface Implementation .
74
5.2 System Testing . . 75
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5.2.1 Test Plan . . . .
75
5.2.2 Hardware Subsystem Testing .
76
5.2.2 Software Subsystem Testing .
77
5.3 Performance Evaluation . .
77
CHAPTER FIVE: SUMMARY AND CONCLUSION AND
RECOMMENDADTION
5.1 Summary of Achievement . .
79
5.2 Problems Encountered and Solution .
79
5.3 Conclusion . . . . 82
5.4 Recommendation . . 80
5.5 Suggestion for Further Improvement .
81
REFERENCES. . 83
APPENDIX A: Full Schematic Diagram .
84
APPENDIX B: Software Details . .
85
LIST OF FIGURES
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1. Fig. 1.1: Block diagram of a PC-Based temperature
controller
2. Fig. 2.2.1: A 2 wire thermocouple
3. Fig. 2.2.2. A typical picture of a thermistor
4. Fig. 2.2.3 A graph of resistance versus temperature for a
typical thermistor
5. Fig. 3.1.1: A structural approach to system analysis
6. Fig. 3.1.2: A block diagram showing the existing system of
temperature monitoring and control system.
7. Fig. 3.1.3: A block diagram model of a PC based 4 point
temperature monitoring and control.
9. Fig. 3.2.1: Modularized approach to system design
10. Fig. 4.2.1: 5/12 Vdc power supply
11. Fig. 4.2.3: Pin-out diagram of ADC0804.
12. Fig. 4.2.4: Diagram showing a minimum configuration of
89C52 microcontroller.
1.3 Fig. 4.2.5: Relay interface to microcontroller
1.4 Fig. 4.2.6 Diagram showing a MAX232 pin-out.
15. Fig. 4.2.7: Connection arrangement of the microcontroller,
MAX232 and DB-9 connector
16. Fig. 4.2.8: Block diagram showing the operation of the
microcontroller
17. Fig. 4.2.9: Project Block Diagram.
LIST OF TABLES
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1. Table 1: Reference table showing the relationship between
baud rate and length of cable for MAX232.
2. Table 4.1: Vref / 2 relationship with Vin range.
3. Table 5.1: Test result for the analog MUX
ABSTRACT
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This project is aimed at designing a temperature monitoring
and controlling system which can be used to monitor the
temperature of industrial processes. This system relies upon
controller, which is connected to temperature, or set point, and
provides an output to a control element. Mostly the control
element is a heater. The controller is connected to a personal
computer using RS232 protocol. The current temperature can
be seen on the PC. This system offers flexibility to controlling
operations because the temperature set point can also be
changed through the user input. It is believed that this project
will remove rigorous and unnecessary monitoring and
controlling activities and hence ensure cheaper and faster
product output. A temperature monitoring system which can be
used to monitor the temperature of industrial processes has
been designed and implemented in the course of this project.
CHAPTER ONE: INTRODUCTION
1.1 Background of the Project
In a typical manufacturing industry, temperature
monitoring makes use of analog temperature controllers.
Such controllers can accept thermocouple input and offer
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imprecise temperature control over a range such as 75 0C
to 1000C. This seemed to pose no disadvantage to them
since their products still sell in the market. However, this
type of controllers used by these industry, unknowingly,
possess no readable display, lack of sophistication for
more challenging control tasks, and no communication
ability, all of which most often expose the industry to the
following problems:
Non-uniform heating rate for a point that requires more
than one heating element, thus causing delay in start-
up of production.
Wastage of raw materials in test-running the line to
ensure that the temperature had reached the minimum
required value
Poor package outlook because the sealers are not
heated
uniformly.
Extra man-power for each extrusion line- one at the
take- off and another at the panel- to ensure that
machine is stopped immediately there is a sign of poor
quality due to failure of one more of the heaters.
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Frequent damage of heating elements as a result of no
precision in control which often leads to over- heating
the elements beyond upper temperature range.
In view of the above limitations, and more, a pc-based
automatic multi- point temperature monitoring and control is
hereby proposed to remove the limitations of analog controllers
and even add flexibility to the control process.
Today, with the continuous price erosion and performance
increase of pc, industrial control is moving from an expensive,
proprietary hardware base to one with foundation of pc-based
software. Pc-based temperature control runs on personal or
industrial hardened computers and provides answers to
initiatives for lean control program.
With the inherent advantages of a pc-based control include
flexibility, high performance, customization, convenience,
easier development, better integration with existing hard
wares, portability and access, the proposed system should be
able to help manufacturing industries solve their problems by
providing uniform heated, precision in measurement and
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control, self monitoring and extension of usage to remote,
inaccessible locations in the manufacturing floor.
1.2 Aims and Objectives
This project PC- based automatic multipoint temperature
monitoring and control is aimed at designing a temperature
monitoring device which can be used to monitor and control the
temperatures of industrial machines. Thus, the complete work
can be viewed as a system having three main features which
serve as the objectives of the work.
PC- based temperature monitoring and control.
Automation facility, which enables the system to be self
monitoring.
Multi-point approach, a feature that makes it possible
for more than one point to be monitored.
Hence, this project is meant to offer flexibility to
monitoring operations by allowing or providing a PC-
interfacing feature
Which allows an operator to monitor the ongoing
process from his PC location at a more convenient and
easy-accessible place, It is believed that this project will
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be able to remove the rigorous activities of monitoring
temperatures by personnel, and engaged him with
other production activities, all aimed at ensuring
cheaper and fast product output.
1.3 Significance of the Study
The beginning of a sweeping change is upon the control
and instrumentation world with the availability of robust
hardware, open technology and real-time, window-based
operating system. PC-based control is emerging as a new
control paradigm for increasing manufacturing
productivity. PC base automatic multi-point temperature
monitoring and control offers open and more intuitive
traditional solutions at a lower total system cost and
easier migration to future technologies. Easier
development, integration, portability, and access, ensure
a flexible and efficient solution. Some of the inherent
advantages of PC-based automatic multipoint temperature
monitoring and control include the following:
Custom User-Interface for Supervisory Control.
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For low-end PID (Proportional Integral-Derivative)
controllers to high end programmable logic controllers
(PCL) system, visualizing the control application can be
very challenging. Many stand-alone controllers have fixed
digital displays for configuring control set-points and
viewing I/O values. PC-based automatic multipoint
temperature controller, being an advanced system, on the
other hand, has a display and typically requires a separate
software package and human machine interface (HMI) to
view and interact with automation systems.
Easy Integrating with Existing System
One may already have a control system that works well for
most needs but could benefit from additional
measurement or advanced control functionality to
optimize certain specialized tasks. A big advantage to
using data acquisition hardware and an open PC platform
is the number of options you have for connecting to
existing equipment. Whether you are communicating with
process instrument, PLC, or single loop controllers, you
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have a variety of ways to integrate a PC-based control
system with existing hardware, this is exactly what a PC-
based automatic multipoint temperature monitoring and
control does in the case of temperature measurement.
Software-defined Control Flexibility.
A PC-based automatic multipoint control system offers you
complete flexibility in defining system functionality and I/O
operations. In addition, even without prior technical skill in
wiring a temperature controller, PC-based automatic
multipoint control system enables an operator to carry out
initial installation since the system just requires relocating
it to another sight without rewiring process (5). Also such
unskilled operator makes changes in the initial setting
using the window-based control interface.
Multipoint Monitoring and Control for Performance
and Reliability.
Beside single point digital temperature controllers which
can control only one process, multipoint digital
temperature controllers control more than one point,
meaning they can accept more than one input variable.
Generally speaking a multipoint controller can be thought
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of a device with many individual temperature controllers
inside one chassis. These are typically mounted behind
the panel in some industrial applications, as opposed to
the front-to-panel (FTP) (9). Multipoint temperature
controllers provide a compact more modular system that
operates either within a stand alone system or in a PLC
environment. They provide a single point of software to
access all control loops.
Enhance Security
PC-based automatic multipoint temperature monitoring
and control systems also have enhance security such as
not having buttons for a person to use and change critical
settings. By having complete control over the information
being read from or written to the multipoint controller, the
machine builder can limit the information that any given
operator can read or change, preventing undesirable
conditions from occurring, such as setting a set point too
high to a range that may damage products or the
machine.
Today, manufacturers around the world look to PC to play
a bigger role in their control system. PCs are already an
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accepted platform for supervisory control, monitoring and
reporting, as well as off-line data management and
analysis. Manufacturers have already realized the
flexibility of the PC and the easy-to-use open architecture
of window-base software applications for manufacturing
environment.
Following the trend, PC-based automatic multipoint
temperature monitoring and control has emerged to
facilitate efficient monitoring and control process for
manufacturing industries. Such temperature controllers
are used in a wide variety of industries to manage
manufacturing processes or operations. Some common
applications include the following.
Heat Treat/Oven
Temperature controllers are used in ovens and in heat
treating applications within furnace, ceramic kilns, boilers
and heat exchangers.
Packaging
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Temperature controllers must maintain a uniform level at
designated temperatures and process time length. This
helps to ensure a high quality product output.
Plastics
Temperature control in the plastic industry is common on
portable chillers, hoppers and dryers, and molding and
extruding equipment, temperature controllers are mused
to precisely monitor and control temperatures at different
critical points in the production of plastics.
Health Care
Temperature control is required in laboratory and test
equipment, autoclaves, incubators, refrigeration
equipment and crystallization growing chambers and test
chambers where specimens must be kept or test must be
run within specific temperature parameters.
Food and Beverage
Common food processing applications involving
temperature control include: brewing, blending,
sterilization and cooking and baking ovens. Controllers
regulate and/or process time to ensure optimum
performance.
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Cable Manufacturing
Insulation materials require as specific temperature which
must be maintained uniformly throughout the barrel and
nozzle zones to ensure good quality of product. Efficient
temperature monitoring and control systems are required
to achieve this.
Finally, the steps taken to incorporate PC to temperature
monitoring and control is one of the many steps required
for a complete computer automation of industrial
processes. Thus, other parameters such as pressure,
colour, texture and so on, can be computerized, providing
a platform for a unified process control.
1.4 Scope of the Work
This work covers the following areas:
Temperature Measurement
Temperature sensors are reviewed and choice made on
the most applicable sensors. The sensor measures the
temperature of the points and converts the reading to a
voltage value. This value is then sent to the
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microcontroller which compares it with the set-point value,
takes appropriate action in order to restore tolerable
limits.
Hardware Programming
High level C-programming language is used to develop
codes for the microcontroller to enable it read the values
sent by the sensors and take appropriate actions. The
Visual Basic Window-based software will be used to
communicate with the PC operating system and the C-
program running on the hardware in order to read the
user set-point values and current temperatures.
Window-based Software Programming
Communication between the hardware and the PC (serial
communication) is facilitated by programming the PC to
be able to communicate with the serial port. The Visual
Basic Window-based software will be used to
communicate with the PC operating system and the C-
program running on the hardware in order to read the
user set-point values and current temperatures.
Level Conversion
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In order to ensure a compatible voltage level between the
hardware and the PC, the MAX 232 technology is
employed. This converts the hardware voltage level to a
voltage which can be handled by the serial port in the PC.
1.5 Block Diagram Overview of the Project Stages
Fig.1.2: Block diagram of a PC-based temperature
controller
A temperature control system relies upon a controller,
which is connected to a temperature sensor. It compares
the actual temperature to the desired control
temperature, or set-point, and provides an output to a
RS232 Interface
PC-based application
MicrocontrollerUnit
Temperature
Sensors
Analog to Digital
Interface
Liquid CrystalDisplay Keypad
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control element. Mostly the control element is a heater.
The controller is connected to a Personal Computer using
RS232 protocol. The Current Temperature can be on the
PC, whereas the Temperature Set-point can also be
changed through the PC or embedded buttons. The
different sections of this project are:
1. Microcontroller
2. Analog to Digital Converter (ADC)
3. Temperature Sensor
4. Relay
5. MAX 232
Microcontroller:
It is the heart of the unit. It performs all the functions like
getting data from ADC, comparing the current
temperature to set-temperature, turning ON/OFF the relay
and communicating with the PC.
Analog to Digital Converter:
The ADC converts the Analog voltage received from the
Temperature Sensor into digital format and gives it to the
microcontroller.
Temperature Sensor:
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The temperature sensor measures the current
temperature and sends value in for of voltage to the
microcontroller. Some IC (e.g. LM35) sensors have output
proportional to the input temperatures.
MAX 232:
Communication with the PC is done through the SERIAL
PORT. The protocol of serial port is RS-232, for interfacing
the controller to the PC using RS-232 protocol, we require
MAX 232 IC.
1.6 Project Report Organization
The design and simulation of the project, PC-based
automatic multipoint temperature monitoring and control
system, followed a systematic approach which reveals a
step-by-step analysis of an existing system, until a
realizable, better system is arrived at. This report covers
the entire steps followed to arrive at the complete
envisaged system. Diagrams and tables are employed,
where necessary, to illustrate facts and results.
Chapter one of this report is an introduction to the project.
It covers the following areas: the project background, aims
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and objectives of the work, justification and scope of the
work and the block diagram overview of the project
stages.
Chapter two is a literature review of related works. In this
chapter, the general concept of temperature control is x-
rayed; different technologies of relevant components are
also reviewed.
In the third chapter, the temperature control technique as
used in an industry is analyzed and shortcomings of the
existing system outlined. Different methods of achieving a
better system are also explored. Then, choice is made
among all the available options. The option chosen is
basically dependent on the nature of the envisaged
system.
Chapter four describes the proper system design. The
input, output and software interfaces are systematically
modularized and designed. The block diagram of the
modules (put together) is also towards the end of this
chapter.
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The whole of chapter five is concerned with the
implementation of the designed system. This involves the
wiring schedules, full schematic diagram and integration
of the different modular designs and schematics,
simulation, testing and performance evaluation, costing
and deployment of the achieved work.
Finally, the last chapter deals with the summary of
achievement, problems encountered during the project
design and implementation stages and the solution
proffered. Recommendations and suggestions for further
improvement are also included.
CHAPTER TWO
REVIEW OF RELATED LITERATURES
2.1 Review of work on Temperature Controllers
2.1.1 . Principle
A temperature controller is a device used to hold a desired
temperature value (2). The simplest example of a temperature
is common thermostat found in homes. All controllers, from the
basic to the most complex, work on the same way. There are
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two variables required by the controller; actual input and
desired set-point value. The input signal is also known as the
process value. The input to the controller is sampled many
times per second, depending on the controller. This input or
process value is then compared with the setpoint value, if the
actual value does not match with the set point, the controller
generates an output signal change based on the difference
between the set-point and the process value, and whether or
not the process value is approaching the set-point or deviating
farther from the set-point. This output signal then initiates
some type of response to correct the actual value so that it
matches the set-point. Usually the control algorithm updates
power value which is then applied to the output.
The control action depends on the type of controller. For
instance, if the controller is an ON/OFF control. The controller
decides if the output needs to be turned on, turned off, or left
in its present state. A temperature controller set control the
temperature inside a room may have its set-point at 68oC and
the actual temperature 67oC. The controller would then send a
signal to increase the applied heat to raise the temperature
back to the set-point of 68oC.
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When analog output is used, the output driver is proportional to
the output power value.
However, if the output is binary output type such as a relay,
SSR driver, or triac, then the output must be time proportioned
to obtain an analog representation.
A time proportioned system uses a cycle time to proportion the
output value. If the cycle time is set to 8 seconds, a system
calling for 50% power will have the output ON for the 4 seconds
and OFF for 4 seconds, while one for 25% power for the same 8
seconds cycle time, will be ON for seconds and OFF for 6
seconds. All things being equal, a shorter cycle time is
desirable because the controller can react quickly and change
the state of the ouput for a given changes on the process. Due
to the mechanics of a relay, a shorter cycle time can shorten
the life of a relay, and is not recommended to be less than 8
seconds. For solid switching devices like SSR driver or triac,
faster switching times are better. The general rule is that, only
if the process will allow it, when a relay ouput is used, a longer
cycle time is desired. (2).
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Typically, all controllers have input and ouput parts. In the case
of a temperature controller, the measured input variable is the
temperature. Temperature controller can have several types of
inputs. The type of input sensors include thermocouples,
resistive thermal devices (RTDs) and integrated circuits (e.g.
LM35). Sensors are treated later in this chapter.
In addition to inputs, every controller also have an output.
Typical outputs provides with temperature controllers include
relay outputs, solid state relay (SSR) drivers, triac and linear
analog outputs. In some cases, the output signal may be
required to retransmit the process to a programmable logic
controller (PLC), recorded or personal computer (PC). In the
case of a PC- based temperature controller, the controller is
connected to a personal computer using the RS 232 protocol. A
software program running on the PC can be used to display the
values on the PC while the set-point can still be changed using
the PC.
2.1.2 Technologies Available
Temperature controllers come in different styles with a vast
array of features and capabilities. There is also plenty of ways
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of categorize controllers according to their functionality. In
general, temperature controllers and either single loop or multi-
loop. Single loop controllers have one input and one or more
outputs to control a thermal system. On the hand, multi-loop
controllers have multiple inputs and outputs, ad capable of
controlling several loops in a process. More control loops permit
controlling more process system functions. Thus, major
development in control technology revolves around increasing
the control capabilities of the controllers.
Reliable single loop controllers range from basic devices that
requires single manual set point changes to sophisticated
profiler that can automatically execute up to eight set-point
changes over time period (2), (9).
The simplest basic controller type is analog controller. Analog
controllers are low cost, simple controllers that are versatile
enough for rugged, reliable process control in harsh industrial
environments including those with significant electrical noise.
Controller display is typically a knob dial. Analog controllers are
synonymous to relay controllers which emerged in the early
60s (9).
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Basic analog controllers are used mostly in non-critical or
unsophisticated thermal systems to provide simple ON/OFF
temperature control for direct or reverse acting application.
Such controllers accept thermocouple or RTD as input sensors,
and they offer imprecise measurement.
Limit controller is another type of controller. It provides safety
limit control over process temperature. They have no ability to
control temperature on their own. Put simply, limit controllers
are independent safety to be alongside an existing control loop.
Limit control is latching and part of redundant control circuitry
to positively shut a thermal system down in output must be
reset by an operator, it will not reset by itself once the limit
condition does not exist.
By early 70s (9), the programmable Logic Controller emerged
with a promising higher control capability. The PLC belongs to
the general- purpose temperature controller and is used to
control most typical processes in industries. Typical, they come
in a range of DIN sizes; have multiple outputs and
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programmable output function. These controllers can also
perform PID control for excellent general control situations.
They are traditionally placed in the front panel with the display
for easy operator accessibility.
Value Motor Drive temperature controllers are specifically
designed to control valve motors used in manufacturing
applications such as gas burner control on a production line.
Special tuning algorithms give accurate control and fast output
reaction without the need for slide ware feedback or excessive
knowledge of three-term PID tuning algorithms-proportional
derivative. Valve motor drive digital controllers are used to
control the position of the valve, somewhere between 0% open
to 0% open, depending on the energy needs of the process at
any given time. They use of ON/OFF Duplex function which is a
very simple algorithm and like its counterpart, ON/OFF control,
is another low cost controller with fast output reaction but low
accuracy.
2.1.3 New Trends
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Modern temperature controllers came out as the need for
automatic calculation of PID parameters for optimal thermal
system performance arose. The PC-based controllers followed
the introduction of MMI/SCADA in the mid 80s (8), replaces the
traditional and proprietary controllers such as PLC, with
standard PC-based hardware and software. PC-based control
runs on personal or industrial hardened computers and
provides answers to initiatives for lean control program. This
PC-based control approach provides end-users and machine
builders with a platform to dramatically reduce control system
design time and maintenance cost by reducing down-time with
built in diagnostic, real time simulation, and consolidation of
data into a single database. Some estimates indicate the PC-
based control market is growing at a rate of over 70 percent a year!
(8).
The PC and desktop software industries are also participating in
this evolution of control with the evolution of window NT.
Window NT version 4.0 is the first Window-based operation
system (6) that provides a truly deterministic, real time
operating system. The advent of many software OS lends PC-
based control more facilities for developing better functionality.
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For example, even without any prior programming experience,
you can use NI LabVIEW graphical development environment to
define custom control functionality and meet your unique
needs. You can build onto the basic LabVIEW application to add
features (6) such as
- Signal processing functions like filtering and averaging;
- Configurable dead banding and hysteresis;
- Data Collection and report generations; and
- Additional input and output channels.
Some manufacturers of temperature controllers have extended
the advantages of PC-based control in designing more
sophisticated controllers such as the profiling digital controllers
or profilers. Profiling digital controllers, also called Ramp-Soak
controllers are controllers that will allow the operator to
program a number of setpoints and the time to sit at each set-
point. The changing of the setpoint is called Ramp and the
time to sit at each set point is called Soak or Dwell. One
remp and one soak are considered to be one segment. A
profiler offers the ability to enter a number of segments to
allow complex temperature profiles. There are many
applications for a profiling controller. The profiles are often
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referred to as recipes by the operator and are often kept on a
computer and downloaded via a communications channel
directly into the controller as needed. Most profilers allow
storage of multiple recipes for later use. Smaller profilers may
allow for 4 recipes with 16 segments each while more
advanced profilers would allow for more. Profile temperature
controllers are able to execute ramp-and-soak profiles such as
temperature changes over time, along with hold and soak/cycle
duration, all the while being unattended by an operator,
allowing the operator to perform other tasks. Typical
applications for profile temperature controllers include heat
treating, annealing, environmental chambers, and in complex
process furnaces.
2.2 Set-up Overview
In this section, the different technologies of the major
components used in this project are explored.
2.2.1 Temperature Measurement and Sensors
Temperature monitoring is central to the majority of data
acquisition systems, be it to save energy costs, increase safety,
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testing time whatever your reasons, you will need a device to
measure the temperature a sensor. Thermocouples,
resistance temperature device (RTDs), thermistors and infrared
thermometers are all types of temperature sensor. Which can
choose depends on factors like your expected maximum and
minimum temperatures, the accuracy you need and your
environmental conditions. The most popular sensors are
thermocouples, RTDs, thermistors and ICs. These are discussed
below, pointing at potential problems when using some of them
in computerized temperature measurement.
Thermocouples
Thermocouples are popular temperature sensors because they
are cheap, versatile and sturdy. They consist of two dissimilar
metals joined together, making a continuous circuit. If one
junction has a different temperature to the other, an
electromotive force (voltage) is set up. This voltage varies with
the temperature difference between the junctions. If the
temperature at one junction is known, the temperature at the
other junction can be calculated.
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Types of Thermocouple
There are several types of thermocouple, labeled with letters
according to their constituent metals. A K-type thermocouple,
for example, is made up of chrome and Alumel. The metals give
the thermocouples differing properties, such as temperature
ranges and accuracy.
Figure 2.2-1: A 2 wire thermocouple
Potential Pitfalls in a Computerized Thermocouple
System
The Cold Junction Reference Measurement. The
system depends on knowing the temperature of one of the
thermocouple junctions (the cold junction). Housing this
junction in an isothermal box will keep the temperature
constant, and a cold junction sensor in the box will tell the
system the temperature. In our plug-in card example, the
VoltmeterCopper wire
Thermocouple
Wires (2 Types)
SensingJunction
ReferenceTemperature
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isothermal box sits outside the computer. You would
connect the thermocouple wires to screw terminals in the
box, and connect the terminals to the card with a ribbon
cable.
Attaching the Thermocouples to Metal Surfaces. if
the thermocouples are directly to a metal surface,
particularly one carrying its own voltage such as heating
element, you need to isolate the signals. This will prevent
high voltages in the monitored item damaging the data
acquisition equipment. It will also make the
measurements floating, letting you record the small
thermocouple voltage in the presence of high voltages.
Linearization. The voltage produced by a thermocouple
does not change linearly with temperature presenting a
problem for the data acquisition system. A good solution is
to use software (7) to obtain the correct temperature in,
say, 0C or 0F. Some custom-made software kits, e.g.
Windmill, can do this automatically for B, E, J, K, N, R, S
and T type thermocouples.
Using the Wrong Type of Thermocouple Lead.
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You need to connect the thermocouple to the data
acquisition equipment using the correct type of extension
or compensation lead. This is made of either the same
material as the thermocouple metals, or material with
similar characteristics.
Long Thermocouple Leads Noisy Signals and
Added Wiring Costs.
Thermocouple leads are often many metres long, and
have a higher resistance than normal copper wire. This
means that the lead can act as aerials, picking up
environmental electrical noise that contaminates the
voltage signal. It might also mean expensive wiring costs.
In this case you need either to take precautions against
nose, or distribute data acquisition units placing them
close to the thermocouples on Modubus, RS485 or
Ethernet networks for example.
RESISTANCE TEMPERATURE DEVICES (RTDs)
Resistance temperature devices (or detectors) rely on the
principle that the resistance of a metal increases with
temperature. When made a platinum, they may be known as
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platinum resistance thermometers (PRTs), and when specified
to have a resistance of 100 ohm at 00C, as Pt 100.
Potential Pitfalls in a Computerized RTD System
Errors Arising from Lead Resistance.
When the resistance to be measured in small, the
resistance in the leads to the RTD can significantly affect
accuracy. Several methods exist for monitoring RTDs,
which address the problems associated with lead
resistance. These methods include balanced bridges and
constant current sources.
Constant current source measurements give
excellent results for all wiring configurations,
including 2-wire, 3 wire, 4-wire and 4 wire
compensated.
The most accurate results are obtained using a 4 wire
arrangement. Each RTD requires the data acquisition
hardware to provide a constant current source. The
current flows through the RTD and the voltage drop the
RTD is measured. Using Ohms law the value of the
resistance of the RTD can be calculated.
Converting the Resistance to a Temperature.
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Software like Windmill automatically converts the resistance
measurement to a temperature in your choice of engineering
units (7).
Thermistors
Thermistors are inexpensive, easily-obtainable temperature
sensors. They are easy to use and adaptable. Circuits with
thermistors can have reasonable output voltages not the
millivolt outputs thermocouples have. Because of these
qualities, thermistors are widely used for simple temperature
measurements. Theyre not used for high temperatures, but in
the temperature ranges where they work they are widely used.
Thermistoers are temperature sensitive resistors. All resistors
vary with temperature, but thermistors are constructed of
semiconductor material with a resistivity that is especially
sensitive to temperature. However, unlike most other resistive
devices, the resistance of a thermistor decreases with
increasing temperature. Thats due to the properties of the
semiconductor material that the thermistor is made from.
Figure 2.2-3 is a graph of resistance as a function of
temperature for a typical thermistor. Notice how the resistance
drops from 100000 ohms, to a very small value in a range
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around room temperature. Not only is the resistance change in
the opposite direction from what you expect, but the
magnitude of the percentage resistance change is substantial.
R
104
102
0 100 200 300 400 500 T (0K)
Fig 2.2-3 Graph of resistance versus temperature for a typical
thermistor.
Sensor (LM 35)
The LM 35 is an integrated circuit sensor that can be used to
measure temperature with an electrical output signal
Fig 2.2-2: A typical picture of a thermistor
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proportional to the temperature in degree Celsisu. Actually IC
temperature sensors consist of integrated temperature
dependent resistors whose output voltage increases
proportionally with increase in temperature due to increased
output resistance. A brief summary of its advantages over
other sensors include:
- more accurate and precise temperature measurement;
- scaled sensor circuitry so that it is not subject to oxidation
and other environmental factors;
- output conditioning of LM35 is simpler when compared to
that of thermocouples, thermistors, etc.
The above inherent properties of IC temperature have made
the more desirable in computerized applications.
2.2.2 Microcontroller
A microcontroller is a single chip microprocessor system which
contains data and program memory, serial and parallel 1/O,
timers, and internal interrupts, all integrated into a single chip.
First microcontrollers were developed in the mid 70s (4). These
were basically calculator-based processors with small ROM
program memories, very limited RAM data memories, and a
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handful of input/output ports. More powerful 8 bit
microcontrollers were later developed. In addition to their
improved instruction sets, these microcontrollers included on-
chi counters/timers, interrupt, 1/O, on-chip ultra-violet erasable
EPROM memory.
The 8051 family was introduced in the early 80s by Intel.
Currently this family of microcontroller has many versions and
some types of included on-chip analog-to-digital converters. In
the 90s, the recent microcontroller, Intel 8951 evolved with all
the features and instruction set of the other trends to
microprocessors. This gives it the ability to be used more easily
with minimum cascading, or even without additional memory
devices. Still in this twenty first century, another Intel 8952,
which is an advanced form of Intel 8951, has been introduced.
Today, microcontrollers have moved into other more powerful,
16 bit market. They are high performance processors that find
application in real-time and computer intensive fields (e.g. in
digital signal processing or real-time control).
2.2.3 Serial Communication
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Communication is essential in electronics system. It can be in
the form or wired or wireless, serial or parallel. The main idea is
to transfer information from one system to another system,
communication in one direction is call a simplex communication
system, and duplex means communication is in both direction
at the same time. Half duplex means that communication is
taking place in both direction but only one direction
communication is taking place at any one time.
Communication between electronics devices usually deals with
logic Is and 0s. a typical electronic system uses the concept of
voltage or frequency. The choice of signal varies.
Voltage/frequency changes can be produced and detected
using simple electronics, so it is relative a easier type of signal
to implement. The information from the sender can be in the
form of voltage. By detecting the voltage, the receiving device
is able to interpret the information. The common understanding
or interpretation of both the sending and receiving device is
known as the communication protocol. The information
conversion to a suitable transmission signal is also known as
encoding. Decoding is the other way round.
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In todays wired communication system, there are a wide
variety of serial communication standard from RS232, RS485,
USB, CAN, and many more. They are simply the standard
defined for communication hardware. Today, various serial
communication interface USART are present. They are TTL
version of the serial communication, represented by 5V/0V. It is
similar to RS232 physical format represented by -/+IOV in the
voltage.
USART is not design for distance communication. To enable
longer communication distance, USART signal will need further
encoding into RS232 signal format before transmission. Other
common names for USART (Universal Synchronous
Asynchronous Receiver Transmitter) are UART or SCI (Serial
Communications Interface). Serial data in TTL format is the very
basic serial communication interface to understand. RS232 is
the encoded version of USART. The encoded signal allows the
data to be deployed for longer communication distance. Some
article may have defined a maximum communication distance
of 15m for RS232 signal. You can try pulling the
communication distance further, it should still works actually.
15rn is only a general guideline.
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If the data transmission rate is low, the distance can even go
further. There have been reports from the internet that some
users have achieved 50m to 200m without any problem. In this
project, I have tried baud rate of 9600bps over 100m without
any problem. Baud-rate is presented in bps (data bits per
second). The higher the value the more the data can be
transmitted in a given time period. The higher the speed, the
shorter the communicationdistance.
The data transmission length of the cable can be determined
by many factors. The factors include the following:
- Data transmission speed
- Quality of the cable, noise (unwanted signal)
- Transmitted voltage '
- Receiver sensitivity
- Etc.
Communication distance using RS232 can be increased further
if the cable is of better quality, a shield or coaxial cable for
example.
The most significant factor is the data transmission speed. The
following is a reference diagram showing regarding the
relationship between data baud rate and cable length.
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Baud-rate Length (distance)
19200bps 15m
9600bps 150m
4800bps . 300m
2400bps . 900m
Table 1: Reference table showing relationship between
baud-rate and length of cable, for MAX232.
1C chip maker has come up with the integrated circuit for
interfacing RS232 with TTL logic (5V for logic 1, 0V for logic 0),
making the interfacing work very simple. MAX232 is one of the
many 1C in the market which helps to convert betweenRS232
-/+10V and TTL +/-5V. The charge pump design allows the
circuit to generate +/-10V from a 5V supply. (See fig. 4.2.7).
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CHAPTER THREE:
METHODOLOGY AND SYSTEM ANALYSIS
3.1
Methodology
Before the inception of the idea that a PC-based system can be
employed to facilitate efficient monitoring and control of
temperatures of industrial processes, a number of steps was
explored in arriving at a conceptual model of the new system.
3.1.1 Structured analysis and design
The steps began with investing and understanding the
current/existing physical system.
The various steps are summarized the diagram below.
EXISTING PHYSICAL SYSTEM
EXISTING LOGICAL SYSTEM
REQUIRED LOGICAL SYSTEM
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REQUIRED PHYSICAL SYSTEM
Figure 3.1-1: Astructured approach to system analysis
Existing Physical/Logical System
As earlier mentioned, Cutix Pic Nnewi, like most other
manufacturing industries, make use of analog temperature
controllers with thermocouple sensors as Inputs. The
concept/logical model of the existing system can be viewed as
shown below:
POWER SUPPLY
CONTROLLER 1
ON/OFF
R1
HEATER1
SENSOR1
HEATER2
HEATER4
HEATER3
SENSOR2
SENSOR3
SENSOR4
R2 R3 R4
CONTROLLER 2
ON/OFF
CONTROLLER 3
ON/OFF
CONTROLLER 4
ON/OFF
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Figure 3.1-2: Existing physical system of temperature
control
and monitoring system.
Considering a four-point temperature control and monitoring
requirement which already was implemented using a separate,
stand alone temperature controllers. Such control can be
achieved using analog controllers or even stand alone PLC.
Each control unit is independent of the other. A problem
statement was formulated after attempting to provide answers
to the following questions:
1. How can the temperature be measured more accurately so
that quality control can be optimized?
2. Can there be a possibility of bringing the control under the
supervision of only one hardware so that easy supervision
an4 surveillance can be made on the process?
3. Can there be a means of establishing a common
communication interface and display so that monitoring can
be done more effectively and abnormality noticed on time
before having 'any damaging effect on the machine or
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product. For instance, when a thermocouple or controller
fails, how can we get a timely notice for its replacement?\
4. How can more security be implemented so that somebody
does not tamper with the set-point on the controller and reset
the knob at a wrong setting.
5. How can the installation process be simplified so that much
time is not devoted to mounting the system in a new place of
interest?
The problem statement can now be formulated: "a need to
design and construct an automatic multipoint temperature
monitoring and control system". Such systemshould have the
following features:
- ability to provide precise and accurate temperature
measurement.
- ability to handle the control of all the four temperatures
that need
to be controlled.
- communication user interface with dip hardware for
monitoring and
controlling the four points almost simultaneously.
- ease of installation without requiring the whole production
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process
be shut down.
- room for integration with other systems if need be.
The Proposed Logical/Physical System
Looking at the deficiencies of the existing system and the
features required of the required system,, a PC-based approach
to system control seems to meet the requirements for the new
system. A physical representation of the proposed model is as
shown below.
CPU
R1
HEATER1
SENSOR1
HEATER2
HEATER4
HEATER3
SENSOR2
SENSOR3
SENSOR4
R2 R3 R4
SINGLE CONTROLLER HARDWARE
SCREEN
POWER SUPPLY
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Figure 3. 1-3: A Block Diagram model of a pc-based 4-
point temperature monitoring and control3.1.2 Top-down Design
Top-down design is the technique of beginning with a complex
project and breaking it down into its constituents. For a supra
system which consists oF several systems and subsystems, a
top-down design approach of such system can be represented
as follows:
SUPRA SYSTEM
SYSTEM
SUBSYSTEM
PROGRAM MODULES
Hence, the project "PC-based automatic multipoint
temperature monitoring and control" is a supra system with
components system as
- temperature controller system, made up of data acquisition
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(or temperature measurement.) unit and control unit; and
- temperature monitoring system, made up of hardware inlet-
facing with PC and user program (Window-base program)
development.
Each of the individual system has its other subsystem and
program modules.
3.1.3 Bottom-up Design
This is a situation where one starts with simple subsystem or
program modules and proceeds to constitute the main system
and subsequently supra system, as the case may be.
3.1.4 Choice Design Approach
The design approach used in this project design is the top-down
design. The whole system is broken down into different smaller
modules.
MODULE 1: Design of the data acquisition system.
This comprises wiring and interconnecting tlic sensors, ADC,
and multiplexers to the microcontroller.
MODULE 2: Configuration of the microcontroller 89C52 and its
control program using C programming language. The MAX232
protocol is also configured at this stage.
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MODULE 3: Design of the PC monitoring Window-based
interface. Here, the Visual Basic (VB 6.0) programming
languagc.is used to write a program that will enable the PC to
communicate with the hardware (controller).
Fig.3.2-1: Modularized approach to the project systemdesign
The final step is integration of the different modules to form the
system required. It is important to note that any of the above
modules can be tackled first and important information that
can be used for the other recorded appropriately for reference
purpose.
3.2 Limitations of the Existing System
It seems appropriate at this point to explicitly enumerate the
major deficiencies of the existing system, which prompted the
MODULE 1
MODULE 2
MODULE3
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design of the new system. From the on-going discussions and
the analysis carried out ab initio, it will be discovered that;
- the old system does not provide a precise temperature
measurement due to the inherent characteristics of the
sensors used;
- monitoring and controlling the temperatures of more than
one point at the same time, using the old system is more
cumbersome and demanding since there are different
controller for each temperature;
- with the old system, a staff should always go round to
observe the controllers at all time to know the one which
is malfunctioning or not functioning at all. This task would
be made easier using a PC-based multipoint temperature
monitoring and control where all events are observed at
a time from one point PC screen.
- Also, there is the possibility of all point being interfered
with by an intruder thereby distorting normal production
parameter settings. Such is minimized with PC-based
system.
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CHAPTER FOUR
SYSTEM DESIGN, SIMULATION AND PERFORMANCE
EVALUATION
4.1 System Specification
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The PC-based automatic multipoint temperature monitoring
and control system is a system that helps users to continuously
monitor the temperaturesof different points of interest at the
same time with the help of a personal computer (PC). The
system will be able to maintain a desired temperature set by
the user at a stable value.
During operation, the maximum value is keyed in by the user.
The current value of the point being monitored must not go
above the maximum set-point. A stable set-point range is
maintained by the microcontroller-based hardware which turns
ON a respective heater for each point whenever the current
temperature reading tends to go below the maximum set-point,
and turns OFF the heater whenever the maximum set- point is
reached. Thus the required temperature is maintained by the
hardware for optimum production operation.
For this project, the range of temperature measurable by the
system is from OC to 100C;
i.e. the maximum set-point must not be any value outside the
range of 0 - 100,
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(0oC < Tmax < 100oC). This system is capable of monitoring
and controlling up to four different points of interest
concurrently but independently.
4.2 Hardware Subsystem
4.2.1 Input Interface
MODULE 1: Design of the data acquisition system. Mere, the
following parts of the project are designed and configured.
- Power supply
- Sensor configuration with the ADC.
Power Supply Design
The power supply requirement for all the components used in
this falls within the 5VDC and 12VDC supplies. Therefore, a
suitable 5V/12DC supply is designed using the following
components: 240/12VAC step-down transformer, a bridge
rectifier 1C, 7505-5V and IN4742 12V voltage regulators and
capacitors of varying specification.
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Fig. 4.1.1: A 5V/12VDc Power Supply Circuit.
The input voltage to the power is to be within the range of 7 to
20 VAC. Here a step-down (240/15VAC) transformer is used to
supply 15VAC to the circuit. The MC7505 5-V regulator and
zener diode 1N4742 are used in the circuit to provide a fixed
5vDcand 12vDc outputs respectively for the system
components. The power supply circuit can handle up to 1A of
current, provided that the transformer can handle the current.
The voltage regulator is provided with heat-sink for easy heat
dissipation.
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Sensor (LM 35)
The LM 35 is an integrated circuit sensor that can be used to
measure temperature with an electrical output signal
proportional to the temperature in degree Celsius. The
summary of its advantages over other sensors have been
discussed in chapter two.
The operational characteristics ofLM35 temperature sensor
includes the following:
- Output voltage that is proportional to the Celsius
temperature;
- accuracy of about +/- 0.4C at room temperature and +/-
0.8C over a range 0C to 100C;
- It draws only about 60uA from its supply and possesses
allow self-heating capability (the sensor self-heating
causes less than 0.1C temperature rise in still air.
Calibrating the LM35 with respect to ADC step output
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The ADC0808 has 8-bit resolution with a maximum of 256 steps
and the LM35 produces l0mV for every degree rise of
temperature. The calibration of LM35 sensor will be such that
for output of 0C to 100C, the input to the ADC ranges from 0to
256 x l0mV, i.e, 0 - 2560mV or 0 - 2.56V.
ADC CONFIGURATIONThe ADC used is ADC0808. It has the frequency
F = 1 HzI.IRC
Where R = 10K, C = 150pF
F = 606 KHz.
Fig 4.2.3: Pin-out diagram of ADC0808
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Vcc: this is +5V power supply pin or a reference voltage pin
when Vref/2 input pin is open.
Vin(+) is used as the only input to be converted when Vin (-) is
connected to the ground.
WR (start conversion) is used to signal the ADC0808 to start
converting the analog input of Vin to an 8-bit digital number,
whenever the pin makes a low-to-high transition.
CS is an active low input used to activate the ADC808.
RD (output enable): A high-to-low RD pulse is used to read the
converted data output of the ADC.
Another parameter to consider in configuring the ADC is the
Vref/2. This determines the step-size of the ADC and
subsequently the digital output of the ADC. The following table
shows Vref/2 relation to Vin range.
VrcI/2(V)
Vin(V) Stepsize(mV)
1
Not 0 to 5 5/256 -19.53
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connected
2.0 0 to 4 4/256=15.62
.i.5 0 to 3 3/256-11.71
1.28 0 to2.56
2.56/256=10.0
1.0 0 to 2 2/256 = 7.81
0.5 0 to 1 1/256 = 3.90
Table 4.1:Vref/2 relationship with Vin range
From the table above, to get a l0.0mV stepsize of the LM35
Vref/2 of value 1.28 is required. This value is achieved by
connecting potentiometer to fix the voltage across the 10K pot
at 25 volts. This should overcome any fluctuations in the power
supply.
Digital output of the ADC is given by;
Dout = VinStepsize
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For example, when the LM35 inputs 250mV to the ADC, the
digital output, from the ADC after conversion should be
Dout = 250mVl0mV
= 25C as temperature reading.
4.2.2 The Control System Design
MODULE 2: The microcontroller is the central control unit in
this project. The microcontroller used in 89C52. The diagram
below shows the pin-out of 89C52.
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Fig. 4.2.4: Pin-out diagram of 89C52 with minimum
configuration
RST: This is the reset input. This input should normally be at
logic 0. A reset is accomplished by holding the RST pin high for
at least two machine cycles.
Power on-reset is normally performed by connecting an
external capacitor and a resistor to this pin. (See fig...)
XTAL1 and XTAL2; These pins are where an external crystal
should be connected for the operation of internal oscillation
device.
P3.0(bit 0 of port 3): This is a bi-directional 1/0 pin with an
internal pull-up resistor. It is also used as the data receive
input (RXD) when the device is used as an asynchronous UART
to receive serial data.
P3.1 (bit 1 of port 3):This is also a bi-directional 1/0 pin with
an internal pull-up resistor. This pin also acts as the data
transmit output (DXT) on the 8051 family when the device is
used as an asynchronous UART to transmit serial data.
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P3.2 (bit 2 of port 3): This is a bi-directional 1/0 pin with an
internal pull-up resistor. This pin is also the external interrupt 0
(INTO) pin.
P3.3 (pin 3 of port 3): This is a bi-directional 1/0 pin with an
internal pull-up resistor. This pin is also the interrupt (1NT1)
pin.
P3.4 (bit 4 of port 3): This is a bi-directional 1/0 pin with an
internal pull-up resistor. This is also the counter 0 input (TO)
pin.
P3.5 (bit 5 of port 3): This is a bi-directional 1/O pin with an
internal pull-up resistor. This pin is also the counter 1 input (TI)
Pin.
GND: This is the ground Pin.
P3.6 (bit 6 of port 3): This is a bi-directional 1/O pin. This pin
is not available on the 89C2025. It is also the external data
memory write (WR) pin.
P3.7 (bit 7 of port 3): This is a bi-directional/1/O pin. On the
standard 8951, this pin is also the external data memory read
(RD) pin.
P1.0 (bit 0 of Port 1): This is also bi-directional 1/O pin. This
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pin has no internal pull-up resistor on the 20 pin devices. It is
also used as the positive input of the analog comparator (AIN0)
on the 20-pin device.
P1.1 (bit 1 of Port 1): This is a bi-directional 1/O pin. This pin
has no internal pull-up resistor on the 20-pin devices. It is also
used as the positive input of the analog comparator (AINI) on
the 20-pin device.
P1.1 (bit 1 of port 1): This is a bi-directional 1/O pin. This pin
has no internal pull-up resistor on the 20-pin devices. It is also
used as the positive input of the analog comparator (AINI) on
the 20-pin device.
P1.2 to P1.7: These are the remaining bi-directional 1/O pins
of port 1. These pins have internal pull-up resistors.
Vcc: This is the voltage supply pin.
Fig.4.2.4 shows that the following external components are
required to have a working microcontroller.
XI-. Crystal (e.g. 12MHz)
Cl.C2:33pF capacitor
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C3; l0uF / 10V electrolytic
capacitor R1:8.2K,0.125W
resistor.
Programming requirement
The microcontroller used in this project was programmed
using the following:
1. Suitable C compiler which generates machine codes for the
microcontroller. The M1DE-51 editor software was used in
this project due to its wide compatibility with C compilers.
4.2.3 Interfacing relay driver to the microcontroller
output port.
The four points being monitored by this system, each has a
sensor and a heater. When the maximum temperature is
exceeded or the minimum temperature more than the current
temperature, a control signal is sent to the respective output
port of the microcontroller for switching ON or OFF a
corresponding heater-as the case may be. Four separate output
pins (P2.0 to P2.3) are used as output to the relay drivers. A
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typical design for interfacing a relay to a microcontroller is
done here.
Fig. 4.2.6: design of relay interface to a microcontroller.
The function of the relay driver is to provide the necessary
current typically 25 to 70mA to energize the relay coil. AN NPN
is used to drive the relay. The transistor is driven to saturation
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(turned ON) when logic 1 is written on the port pin thus turning
ON the relay. The relay is turned OFF by writing logic 0 on the
port.
A diode is connected across the relay coil to protect the
transistor from damage due to back emf generated in the
relay's inductive coil when the transistor is turned OFF. When
the transistor is switched off, the energy stored in the inductor
is dissipated through the diode and the internal resistance of
the relay coil. A pull-up resistor is used at the base of the
transistor. The microcontroller 8052 has an internal pull up
resistor of 10K, so when the pin is pulled high (logic 1), the
current flows through tins resistor. The maximum output
current is
5V = 0.5mA10K
BC547 has a DC current gain of 100, so the maximum collector
current is
0.5x100-50mA
This value is not enough to turn the transistor to saturation.
Therefore, an external pull-up resistor is used. When the
controller pin is high, current flows through the controller pin as
well as through the pull-up resistor. For the circuit shown, a
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4.7K pull-up resistor is used; so the current added to the base
current is
5V = 1.1mA4.7K
Hence, the total base current is (0.5+1.1) mA = 1.6mA.
The maximum collector current is I.6mAxlOO = 160mA, which
is enough to turn ON the relay driver- BC547.
NB: The same arrangement is connected to each of the four
output pins connected to the four different heaters,
Interfacing aMAX232 technology to a Microcontroller
The MAX232 diagram below shows that it has two sets of line
drivers: Rl, Tl and R2,T2. The communication cable from the
hardware through the MAX232 is connected to the PC port
using the DB-9 connector.
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Fig. 4.2.7: Diagram showing a MAX232 pin-out
The diagram below shows the pin connections(pin-outs) of a 9-
way serial port. Each pin has a two of three letter mnemonic as
follows:
GND 5
DTR 4 RI 9
TXD 3 CTS 8
RXD 2 RTS 7
CD 1 DSR 6
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Pin # Mnemonic Meaning
1 CD - Carrier
Detect
2 RXD -
Receive Data
3 TXD - Transmit
Data
4 DTR - Data Terminal Ready
5 GND - Ground
6 DSR - Data Set Ready
7 RTS - Request To Send
8 CTS - Clear To Send
9 RI - Ring Indicator
For a simple serial communication there are three pins that are
important. Data is transmitted over one pin (Transmit Data or
TXD for short) and received over another pin (Receive Data or
RXD). The third wire that's needed is the Ground wire (GND) -
serving as a return path for the electrical signal. It is important
to ensure that the TXD and RXD of the two computers are
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interchanged during wiring. That is, the RXD pin of one port
must be connected to the TXD pin of the second and so on. This
means that when COMI transmits data (on TXD) controller
hardware will receive data on RXD, and vise versa. The
complete wiring between the two connectors looks like this:
COMI CONTROLLER
RXD 2 TXD 3
TXD 3 RXD 2
GND 5 GND 5
Also, in order to allow data transfer between the PC and a
microcontroller- based system without any error, there is need
to make sure that the baud rate of the PCs COM port matches
the baud rate of the microcontroller. This should be taken care
of during software programming.
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4.3: Software Subsystem Design
4.3.1 Program Block Diagram and Control Algorithm
Program Block Diagram:
Various steps taken in programming the microcontroller using C
programming language are shown in the following block
diagram.
Initialize ADC
InitializeSerial-port
Update threshold
Controller Addresschange
Start Conversion
ReceiveTemperature
Monitor and ControlTemp.
Send temperature
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Fig. 4.2.8: Block diagram showing the operation of themicrocontrollerThe Control Algorithm
The control algorithm is implemented in the control sub-
program and is used by the microcontroller to control the entire
system when the temperatures (Tmax) are sensed, converted
to volts, digitized and displayed by the microcontroller.
BEGIN
DO
GET Tmax
IF T < Tmax THEN
Turn ON heater
ELSE
TURN OFF HEATER
LOOP
4.3.2: Configuring the serial ports
Before the microcontroller serial port can be used it is
necessary to set various registers.
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SCON: this is the serial port control register. It should be set to
hexadecimal 0x50 for 8-bit data mode.
TMOD: This register controls the timers for baud rate
generation, and it should be set to hexadecimal 0x20 to enable
timer 1 to operate in 8-bit auto-reload mode.
TH1: This register should be loaded with a constant so that the
required baud rate can be generated. A method for determining
the values to be loaded into THI is discussed later.
TR1: This register starts/stops the timer and it should be set to
1 to start timer 1. T1: This register should be set 1 to indicate
ready to transmit signal.
Determining TH1 value
The value of be loaded into the TH1 register is dependent on
the crystal oscillator value and the required baud rate. Dividing
1/12 of the crystal frequency by 32 gives the default value
upon activation of the 8052 RESET pin. With XTAL = 12.00MHz,
we can determine the TH1 value needed to have 9600 baud
rate as follows
XTALOSCILLATOR
12 32 BAUDRATE
TH1VALUE
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Give a machine cycle frequency of 8052 as 12.00MHz. We
determine the TH1 value:
12.00MHz/12 = 1000 KHz;
1000 KHz/32 = 31250: the freq. of UART to timer 1 to
set baud rate.
31250.9600 = 3.255: TH1 value
Hence, setting TH1 value to 3(=FD hex) gives an error of 7%
In programming the 8952 to transfer character byte serially;
1. TMOD register is loaded with the value 20H, indicating the
use of timer 1 in mode 2 (8-bit auto-reload to set baud
rate).
2. The TH1 is loaded with the value 0xFD to set baud rate for
serial data transfer.
3. The SCON register is loaded with the value 50H, indicating
serial mode 1, where an 8-bit data is framed with start and
stop bits.
4. TR1 is set to 1 to start timer 1
5. T1 is cleared by CLR T1 instruction.
6. The character byte to be transferred serially is written into
SBUF register.
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7. The T1 flag bit is monitored with the use of instruction JNB
T1, xx to see if the character has been transferred
completely.
8. To transfer the next byte, go to step 5.
Steps 1-4 indicate how to initialize the serial port for 9600 baud
rate. Using C programming language, steps 1-4 are shown
below.
Void serial init0
SCON = 0x50;
TMOD = 0x20.
TH1 = 0xFD;
TR1 = 1;
T1 = 1;
Also, in programming the 89C52 to receive character byte
serially, the same steps 1-4, except step 5, are to be followed.
At step 5, R1 register is cleared by CLR R1 instruction. The
same R1 flag bit is monitored with the use of JNB R1, xx
instruction to see if an entire character has been received yet.
When R1 is raised, SBUF has the byte. Its contents are moved
into a safe place.
4.3.3 Configuring the PC Serial port using Visual Basic
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MODULE 3:
Visual Basic (VB) comes with a ready-made component for
handling communication ports, the MsComm control. MsComm
is a simplification of the underlying API call for controlling a
communication port. In programming for serial communication
using MsComm in VB, one has to initialize button that opens the
ports and configure the settings for baud rate, parity, data bits
and stop bits and sets off a polling loop. Here I have used baud
rate of 9600, data bits of 8, no parity, i.e. parity (none) and one
stop bit. One can initially set COM1 (and COM2) up with both
RTS and DTR set off:
With MSComm 1
.MsComm1-settings = 9600, 8, N, 1
.DTREnable = False
.RTSEnable = False
.CommPort = 1
.PortOpen = True
End With
One set up the program just polls for input and rest of the
program can be written as shown below. The complete program
is attached as part of appendix B.
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Do While MSComm1. PortOpen
S1 = MSComm 1. Input
(Program body)
:
:
:
Else
DoEvents
End If
Loop
Program Description
When microcontroller changes address and send address code
to the PC serial port, the Vb program understands it to mean
ready and it activates the object, say Temperature 1, and it
sends the Tmax for the object. The microcontroller receives the
value and stores in SBUF of the microcontroller. Then it
initializes the ADC to start conversion. After, it reads and sends
the value of PC as Current temperature. The VB obtains the
value and displays it in the TEMP box. The microcontroller
performs control operation with the current temperature,
comparing it with Tmax. It then takes the required action
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depending on the outcome of the comparison. After the control
operation, the microcontroller changes address and sends code
to the Vb on the PC to activate another object, say
Temperature 2. It then repeats the whole steps taken for
temperature 1. Such steps are also taken for the Temperatures
3 and 4, and cycle repeats continuously.
4.4 The Input / Output arrangement
The whole system, made up of the microcontroller-based data
acquisition hardware, the PC-interface and the relay outputs, is
arranged having the microcontroller-based hardware as the
central system. This system receives inputs from both the
temperature sensors and the PC interface. The outputs that go
out of the microcontroller include the following:
- Current temperature for display
- Control signal to the relay drivers to switch ON or OFF
the respective heaters.
- Control signal to ADC to start conversion of the next
temperature after processing the previous reading.
- Control address bits to the MUX to switch to next
sensor.
4.5 Project Block Diagram
Liquid
POWER SUPPLY
ANALOGTO
DIGITALCONVERTER
SENSOR 1
SENSOR 2
SENSOR 3
SENSOR 4
RELAY
MICRO-CONTROLLER
MAX232
PC
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Fig.4.2.9: Block diagram of the project
4.6 SIMULATION OF THE SYSTEM
Having successfully completed the designs, the block diagram,
system specification and design, the actual implementation
was done using simulation software. Proteus ISIS is a suitable
simulation tool for microcontroller based designs. So the
microcontroller hardware is implemented with proteus
application software. This involves integration of different
components of the system to achieve a complete working
system.
4.6.1 Input interface implementation
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The input interface, with respect to the microcontroller-
based hardware, is made up of:
1. temperature sensor circuitry
2. 4-channel analog-to-digital converter (ADC)
Temperature sensor circuitry
Four LM35 temperature sensors are connected to four input
channels of the ADC0808. The diagram below illustrates the
wiring diagram of the sensors and the ADC.
Fig. 5.1.2: Circuit diagram showing the wiring schedule
of the input interface to the Microcontroller.
4.6.2 The Control System Implementation
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The microcontroller is configured for normal operation, i.e.
connecting the power-on-reset, the crystal oscillator.
Then, the controller is connected to the input interface of
figure 5.1.2.
4.6.3 The Output Interface Implementation
The output of the system includes the signal that triggers
the relay drivers to switch a corresponding heater ON or
OFF. This signal comes from the output port 1 (p1.0 - p1.3)
of the 8952 microcontroller. The implementation of the
output interface connected to the input section is shown in
the diagram below.
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Fig. 5.1.4: Diagram showing output and input interfaces
to microcontroller
4.7 System simulation test
The PC-based automatic multipoint temperature
monitoring and control system essentially comprises two
basic parts, namely: the hardware and the software parts.
So far, the hardware has been implemented. A systematic
test of the hardware on proteus is to be done. At this
point, the embedded software is loaded to the
microcontroller and every aspect of the hardware tested.
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The temperature inputs are simulated while the variation
in the temperature is observed on the LCD. The serial
virtual tool is used to view what the m