m. lakshmi prasad - shodhgangashodhganga.inflibnet.ac.in/bitstream/10603/33375/1/srama... ·...
TRANSCRIPT
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DESIGN AND DEVELOPMENT OF EMBEDDED BASED PHOTOACOUSTIC
SYSTEM FOR THE MEASUREMENT OF AIR POLLUTANTS IN
INDUSTRIAL AND AUTOMOBILE EMISSIONS
Thesis submitted to
SRI KRISHNADEVARAYA UNIVERSITY ANANTAPUR - 515 003 (A.P) INDIA
By
M. LAKSHMI PRASAD
In partial fulfillment for the award of the degree of
DOCTOR OF PHILOSOPHY IN
INSTRUMENTATION
Under the Supervision of
Prof. K. MALAKONDAIAH
DEPARTMENT OF INSTRUMENTATION SRI KRISHNADEVARAYA UNIVERSITY ANANTAPUR – 515 003
JANUARY 2013
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“I have heard articulate speech by sunlight! I have heard a ray of the sun laugh
and cough and sing! ...I have been able to hear a shadow and I have even
perceived by ear the passage of a cloud across the sun's disk”
-Alexander Graham Bell
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DEDICATED
TO
MY FATHER
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SRI KRISHNADEVARAYA UNIVERSITY Anantapur - 515 003, A.P., INDIA
Prof. K. MALAKONDAIAH, M.Sc., Ph.D. (Retd)
Department of Instrumentation and
University Science Instrumentation Centre
Sri Krishnadevaraya University
Anantapur -515 003
Office : 08554 -255881
Res : 08554 -244150
Email : [email protected]
CERTIFICATE
This is to certify that the thesis entitled “Design and Development of Embedded
Based Photoacoustic System for the Measurement of Air Pollutants in Industrial
and Automobile Emissions” submitted by Mr. M. Lakshmi Prasad is a bonafied
record of the research work done by him during the period of study under my
supervision, and that it has not previously performed the basis for the award of any
degree, diploma, associateship, fellowship or other similar titles to the candidate.
Date : Prof.K. MALAKONDAIAH
Place : Anantapur Research Supervisor
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DECLARATION
I declare that the thesis entitled “Design and Development of Embedded Based
Photoacoustic System for the Measurement of Air Pollutants in Industrial and
Automobile Emissions” submitted for the award of Doctor of Philosophy in
Instrumentation is entirely new and original and has not submitted to any other
University for the award of any other degree or diploma.
Date :
Place : Anantapur (M. LAKSHMI PRASAD)
Research Scholar
Department of Instrumentation
Sri Krishnadevaraya University
Anantapur-515 003
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CONTENTS
PREFACE i
Chapter 1 : Introduction
1.1 Introduction to air pollutants 1
1.2 Introduction to photoacoustic spectroscopy 6
1.3 A brief review of earlier experimental techniques 8
1.4 Role of embedded systems in Instrumentation 18
1.5 Purpose and scope of the present study 28
References 30
Chapter 2: Design and Development of Embedded Based Photoacoustic
Measurement System: Hardware Design
2.1 Principle 33
2.2 Functional block diagram 35
2.3 Radiation source 36
2.4 Modulator for radiation source 39
2.5 Photoacoustic cell 42
2.6 Acoustic detector 49
2.7 Low noice pre-amplifier 51
2.8 Lock-in amplifier unit 53
2.9 Temperature sensing unit 58
2.10 Pressure sensing unit 60
2.11 Analog to digital converter 62
2.12 ARM Microcontroller unit 65
2.13 Liquid crystal display 68
2.14 Power supply unit 72
2.15 Schematic diagram and working 73
2.16 Sample handling unit 75
References 76
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Chapter 3 : Design and Development of Embedded Based Photoacoustic
Measurement System: Software Development
1. Salient features of embedded C language 78
2. Software development 87
3. Program in detail 93
3.4 Calibration and measurement procedure 102
References 104
Chapter 4 : Standardization of Embedded Based Photoacoustic Measurement
System
4.1 Introduction to standardization 105
4.2 Response of the photoacoustic resonant cell 106
4.3 Standardization of the system with nitrogen dioxides 108
4.4 Results and discussion 110
References 117
Chapter 5 : Measurement of Nitrogen Oxides in Industrial Emissions
Industrial emissions 118
Nitrogen oxides pollutant 122
Experimental procedure 126
Results and discussion 127
References 130
Chapter 6 : Measurement of Carbon Soot Pollutant in Automobile
Emissions
Automobile emissions 131
Carbon soot pollutant 133
Calibration and measurement procedure 136
Results and discussions 139
References 142
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Chapter 7: Measurement of Carbon Monoxide Pollutant in Industrial and
Automobile Emissions
1. Industrial and automobile emissions 143
2. Introduction to carbon monoxide 146
3. Calibration and measurement procedure 149
4. Results and discussion 152
References 157
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PREFACE
Instrumentation, a central feature for all scientific and technological activities, plays a
pivotal role in all aspects of human endeavor. The photoacoustic spectroscopy, a new
impetus to the field of analytical sciences, with the combined features of laser sources
and sensitive photoacoustic detection system offers a great potential for pollution
monitoring. The advent of embedded processors further has enhanced the design of
these instruments which improves their quality and versatility.
One of the most concerning problems faced by the modern society is the
atmospheric pollution which causes dangerous environmental hazards such as the
degeneration of air quality, acid rain, photochemical smog, ozone layer depletion, health
diseases and the global warming. Air pollution in India has been aggravated over the
years due to the growing cities, increasing traffic, rapid economic development and
industrialization and higher levels of energy consumption. In India, air pollution is
restricted mostly to urban areas, where automobiles are the major contributors, and to a
few other areas with a concentration of industries and thermal power plants. The major
sources of air pollution in the country are industries (toxic gases), thermal power plants
(fly ash, oxides of nitrogen, carbon monoxide and sulphur dioxide), and motor vehicles
(carbon monoxide, soot particles, hydrocarbons and oxides of nitrogen).
No doubt, several investigators have developed the techniques for measurement
of air pollutants in different emission zones and several manufacturers produced a
variety of instruments for different pollutant estimations. But these are conventional,
indirect methods and suffer from many disadvantages. Hence, in the present study, an
attempt is made to design and fabricate an embedded based photoacoustic system for
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measurement of air pollutants such as nitrogen oxides, carbon soot and carbon
monoxide in industrial and automobile emissions.
The work presented in the thesis is divided into seven chapters, each chapter
being sub-divided into several sections. The first chapter is introductory. In section
1.1, the air pollutants and their environmental and health effects are discussed. The
section 1.2 explains the basic principles and brief history of photoacoustic
spectroscopy. A brief review of earlier experimental techniques for air pollutants is
presented in section 1.3. The role of embedded instruments in instrumentation is
given in section 1.4. The section 1.5 deals with the purpose and scope of the present
study.
Chapter 2 deals with the hardware design aspects of embedded based
photoacoustic system for measurement of air pollutants. The principle of working of the
system is explained in section 2.1. The functional block diagram of the system is
presented in section 2.2. The laser radiation sources employed in the present study are
described in section 2.3. The XR 2206 is an on-chip function generator which serves as
a modulator for laser source is designed in the present study. The details are given in
section 2.4. The photoacoustic cell is the heart of the photoacoustic spectrometer that
deserves a special attention in its design. The design and fabrication details of a
photoacoustic cell are explained in section 2.5. A high sensitive professional electret
microphone is used as an acoustic detector in the present study whose details are
presented in section 2.6. The design features of low noise preamplifier are presented in
section 2.7. The lock-in amplifier which contains four different sections - preamplifier,
bandpass filter, phased lock loop and phase sensing detector plays a significant role. The
design features are described in section 2.8. The sections 2.9 and 2.10 are devoted for
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temperature and pressure sensing units which are essential to monitor temperature and
pressure in the system. The details of high speed analog to digital converter and its
salient features are given in section 2.11. The ARM 32-bit microcontroller LPC2106 is
used as an embedded processor in the present study. The hardware details along with its
interfacing mechanism are explained in section 2.12. The section 2.13 gives the details
of 20x4 characters liquid crystal display unit and its interfacing with the embedded
microcontroller. The regulated power supply which supplies the required power to all
the functional units of the system is designed in the present study and it is explained in
section 2.14. The schematic diagram, construction and its working details are presented
in section 2.15. The section 2.16 gives the details of sample handling system.
Chapter 3 is devoted for software development of the present study.
Embedded C is a popular programming language for microcontroller based systems.
The section 3.1 deals with the salient features of embedded C language. The section 3.2
describes the software development such as software routines and flow charts of the
system designed in the present study. The program, in detail, is given in section 3.3.
The calibration and measurement procedures are explained in section 3.4.
Chapter 4 deals with the calibration of the system. The section 4.1 is
introductory. The response of photoacoustic resonance cell is discussed in section
4.2. The standardization of the system with standard nitrogen dioxide samples is
explained in section 4.3. The results of measurements are presented section 4.4.
Chapter 5 deals with the application of the system for measurement of nitrogen
oxides (NOx) pollutant in industrial emissions. NOx is one of the most prominent air
pollutants and poison by inhalation. Some of the industries of Hyderabad and Ranga
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Reddy district area are chosen for the measurement of nitrogen oxides with the system
developed in the present study. The common industrial emissions and their contribution
to pollution are discussed in section 5.1. The significance of nitrogen oxides as
pollutants is given section 5.2. The experimental procedure for nitrogen oxides pollutant
is described in section 5.3. The results of measurements are presented in section 5.4.
Chapter 6 deals with the application of the system for measurement of carbon
soot pollutant in industrial and automobile emissions. Carbon soot plays a major role in
environmental degradation and global warming. Some of the industries and automotive
vehicles emissions of Hyderabad and Ranga Reddy district area are chosen for the
measurement of carbon soot with the system developed in the present study. The section
6.1 gives the introduction about automobile emissions. The significance of carbon soot
as pollutant is given section 6.2. The calibration and measurement procedure for carbon
soot pollutant is described in section 6.3. The results of measurements are presented in
section 6.4.
Chapter 7 deals with the application of the system for measurement of carbon
monoxide pollutant in industrial and automobile emissions. Carbon monoxide is a
colorless, odorless and tasteless gas which is highly toxic to human being and animals.
Some of the automotive vehicles of Hyderabad area are chosen for the measurement of
carbon monoxide with the system developed in the present study. The industrial,
automobile emissions and their contribution to pollution are discussed in section 7.1.
The significance of carbon monoxide as pollutant is given section 7.2. The calibration
and measurement procedure for carbon monoxide pollutant is described in section 7.4.
The results of measurements are presented in section 7.5.
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The embedded based photoacoustic system designed and developed in present
study is quite successful in the measurement of air pollutants - nitrogen oxides, carbon
soot and carbon monoxide in the given samples of industrial and automobile emissions
with an accuracy of ±1ppm.
I convey my deep sense of gratitude to my beloved teacher and research
supervisor Prof. K. Malakondaiah (Retd), University Science Instrumentation Centre
and Department of Instrumentation, Sri Krishnadevaraya University, Anantapur for his
valuable guidance and constant encouragement in carrying out my research work.
I am very thankful to Prof. C. Nagaraja, Head, Department of Instrumentation,
Sri Krishnadevaraya University, Anantapur for his help and encouragement. I am
thankful to Dr. S. Allahbaksh (Retd), Prof. B. Rama Murthy and Prof. K. Nagabhushan
Raju, Department of Instrumentation and University Science Instrumentation Centre,
Sri Krishnadevaraya University, Anantapur for their helpful suggestions. I am grateful
to Prof. P. Bhaskar, Gulbarga University Postgraduate Center, Raichur, Karnataka state
for his valuable suggestions and help.
I convey my deep sense of gratitude to Sri Ramesh Datla, Managing Director,
ELICO Limited, Hyderabad for his kind cooperation, encouragement and generous
support to carry out my research work. My sincere thanks are due to Sri K.V.S.N. Raju,
Sri J.P. Reddy, Dr. Gayatri Hela, Sri K.V.S.K. Prasad and Sri N.J.R. Srinvas,
Department of Technology Services, ELICO Limited, Hyderabad for their helpful
suggestions. I am thankful to Dr. G. Satheesh Babu, BPL Limited, Bangalore for his
valuable suggestions.
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I am thankful to my beloved wife Mrs. P. Anuradha and other family members for
their continuous cooperation and support in carrying out my research work. Words
cannot express my deep sense of gratitude to my mother and brother for their support
and encouragement.
I express my sincere thanks to my research colleagues in the Department of
Instrumentation - Mr. Ramana, Mr. Raja Rao, Mrs. Anjulatha, Mr. Ashok, Mr. Anand,
Mrs. P. Sushama, Miss V. Sailaja and other research scholars for their cooperation and
help..
I am very grateful to the authorities of Sri Krishnadevaraya University,
Anantapur and M/s ELICO Limited, Hyderabad for providing me the necessary
facilities to carry out my research work.
M. LAKSHMI PRASAD
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CHAPTER 1
Introduction
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Section 1.1
INTRODUCTION TO AIR POLLUTANTS
Clean air is most important to human beings, because we cannot live without air for
more than a few minutes. There are many substances in the air which are harmful to the
health of human being, animals and plants. Harmful substances are arising day-to-day
from human activities and natural processes. However these substances are found
greater concentration in the air as a result of human activities which are generally
referred as air pollutants1. The air pollutants cause severe health disorders in human
being. It is necessary to analyze the air pollutants and take the necessary precautions.
The measurement of air pollutants in air is very essential to warn and educate the people
on its toxic effects.
The air pollutants can be classified into two categories primary air pollutants and
secondary air pollutants. The primary air pollutants are substances that directly emit into
the atmosphere from volcanic2 explosion and secondary air pollutants do not emit
directly which form when the primary pollutants interact with other pollutants. The
most of air pollutants produce from human activities which are briefly described.
1. Nitrogen dioxide pollutant
Nitrogen dioxide (NO2) is one of the several nitrogen oxides. It is a reddish-brown,
pungent and acidic gas which is corrosive and strongly oxidizing. Nitrogen dioxide (3,4)
is one of the most prominent air pollutants and poison by inhalation. It does not usually
release directly into the air, which forms in the air when nitrogen oxide react with other
chemicals. The main source of nitrogen dioxide is the combustion of fossil fuel such as
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coal, oil, gas etc. In cities, motor vehicles are contributing about 80% of ambient
nitrogen dioxide. Nitrogen dioxide causes smog and acid rain.
2. Carbon monoxide pollutant
Carbon monoxide(5,6)
is a colorless, odorless and tasteless gas which is highly toxic to
human beings and animals. It consists of one carbon atom and one oxygen atom. It
produces from incomplete combustion of carbon based fuels such as petrol, diesel,
wood etc. Motor vehicles produce carbon monoxide about 60 percent of carbon
monoxide nationwide. In cities, it may be as high as 90 percent. Other sources include
industrial processes, non-transportation fuel combustion and wildfires.
Carbon monoxide enters the bloodstream through the lungs and reduces oxygen
delivery to the body's organs and tissues. The health threat7 from carbon monoxide at
low levels is most serious for those who suffer from cardiovascular disease, such as
angina pectoris. At much higher levels, carbon monoxide can be poisonous. Even
healthy people may be affected. Visual impairment, reduced work capacity, reduced
manual dexterity, poor learning ability and difficulty in performing complex tasks are
all associated with exposure to carbon monoxide.
3. Sulfur dioxide pollutant
Sulfur dioxide (SO2) is a colorless gas. It belongs to the family of sulphur oxides(8,9)
.
Sulfur dioxide reacts on the surface of airborne solid particles. It is soluble in water and
it can be oxidized within airborne water droplets. The most important man-made
sources of sulphur dioxide are fossil fuel combustion, smelting, manufacture of sulfuric
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acid and conversion of wood pulp to paper production. The coal burning is largest man-
made source of sulphur dioxide accounting for about 50% of annual emissions. The
major health effects are respiratory illness, pulmonary disease and cardiovascular
disease. In the atmosphere, sulphur dioxide mixes with water vapor producing sulphuric
acid which can be transported by wind over many hundreds of kilometers and
deposited. Sulfur dioxide causes acid rains.
4. Carbon dioxide pollutant
Carbon dioxide (CO2) is a colorless gas. It contains two oxygen atoms and single carbon
atom. CO2 is a odorless at low concentrations. It has a sharp and acidic odor at higher
concentrations. Carbon dioxide10
is obtained from the combustion of coke/coal or other
carbon containing fuels
C + O2 → CO2
In most of the areas, carbon dioxide is generated as a by-product of the combustion of
fossil fuels such as coal, oil, natural gases and other chemical processes. Carbon dioxide
acts as an asphyxiant and an irritant when inhaled at higher concentrations than usual
atmospheric levels. It can produce a sour taste in the mouth and a stinging sensation in
the nose and throat.
5. Carbon soot pollutant
Carbon soot is one of the air pollutants. It is a general term that refers to impure carbon
particles resulting from the incomplete combustion of a hydrocarbon. Carbon soot(11,12)
is in the general category of airborne particulate matter which is considered hazardous
to the lungs and general health, when the particles are less than five micrometers in
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diameter such particles are not filtered out by the upper respiratory tract. Carbon soot
emits from various sources such as internal combustion engines, power plant boilers,
ship boilers, central steam heat boilers, waste incineration, local field burning, house
fires, forest fires, furnaces etc.
6. Ozone pollutant
Ozone (O3) is a triatomic molecule which consists of three oxygen atoms. The
ozone(13,14)
occurs naturally in the upper layers of the atmosphere. Ozone is an
important gas which shields the earth from harmful ultraviolet rays of the sun. However,
ozone is an air pollutant and highly toxic gas at the ground level. It causes itching and
burning of our eyes. It also reduces our resistance to cold and pneumonia. The motor
vehicles and industrial emissions are the major cause to increase the ground-level
ozone.
7. Suspended particulate matter
Suspended particulate matter(11,15)
are tiny particles of solid or liquid matter suspended
in air. The tiny particles are less than 10µm in diameter which tend to stay suspended in
the atmosphere for a long period of time. These fine particulates (16-17)
are small enough
to bypass the screening of the nose. They can penetrate alveoli and deposit in the upper
respiratory tract. The large number of deaths and other health problems are associated
with particulate matter. Particulate matter has been emitting from fuel combustion in
motor vehicles, process combustion and industrial exhaust. They also are formed from
reactions of other pollutants like NOx, SO2 and hydrocarbons.
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Emission sources of air pollutants
The different emission sources emit air pollutants into atmosphere in the form of gases.
They can be classified into the following two major categories
2. Anthropogenic emission sources
3. Natural emission sources
Anthropogenic emission sources
Anthropogenic describes something that is made by human beings. Anthropogenic
emission sources are mostly related to burning of various kinds of fuel which are
described as follows
(i) Stationary sources18
, which include smoke stacks of power plants,
manufacturing industries and municipal waste furnaces.
(ii) Mobile sources19
such as motor vehicles, aircraft, container ships and related
port air pollution.
(iii) Fumes, which generates from paint, hair spray, varnish, aerosol sprays and other
solvent manufacturing industries.
(iv) Military such as nuclear weapons, toxic gases, germ warfare and rocketry.
Natural emission sources
(i) Methane, which emits from the digestion of food of animals.
(ii) Smoke and carbon monoxide, which emit from wildfires.
(iii) Volcanic activity, which produces sulfur, chlorine and ash particulates.
(v) Dust, which can form from natural sources usually large areas of land with little
or no vegetation
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Section 1.2
INTRODUCTION TO PHOTOACOUSTIC SPECTROSCOY
Photoacoustic spectroscopy (PAS) is based on the absorption of electromagnetic
radiation by analyte molecules. Non-radiative relaxation processes20
lead to local
warming of the sample matrix. The pressure fluctuations are generated by thermal
expansion, which can be detected in the form of acoustic waves.
The photoacoustic effect was discovered by Alexander Graham Bell(21-22)
in
1880. He found that thin discs emit sound when exposed to a rapidly interrupted beam
of sunlight. By placing different absorbing substances in contact with the ear using a
hearing tube, he was able to detect absorption in both the visible and the invisible
regions of the solar spectrum. This spectrophone was used in his experiments on
wireless transmission of sound. After additional experiments are done by Tyndall and
Rontgen and some initial analytical applications in the year of 1930 and interest in the
photoacoustic effect declined over the following decades. The first applications of the
effect to trace gas monitoring were reported in the late 1960. Important steps leading to
this rediscovery of the effect for analytical purposes were the invention of the laser as
an intense light source and the development of highly sensitive sound detectors such as
condenser microphones and piezoelectric transducers. The first comprehensive
theoretical description of the photoacoustic effect was found in solids by Rosencwaig
and Gersho23
(R&G) theory.
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In the 1970s and 1980s photoacoustic gas detection24
is boomed. The high
sensitivities are achieved by using the gas lasers and solid state laser such as CO, CO2
and DPSS lasers in photoacoustic systems. The high output power and their line
tunability to be ideal sources to push the sensitivity of photoacoustic (PA) gas detection
into the ppbV (parts per billion volume) concentrations or even below.
Photoacoustic effect
The photoacoustic effect is a conversion between light and acoustic waves due to
absorption and localized thermal excitation25
. When rapid pulses of light are incident on
a sample of matter, they can be absorbed and the resulting energy will be radiated as
heat. This heat causes detectable sound waves26
due to pressure variation in the
surrounding medium. With the invention of the microphone and laser, the photoacoustic
effect took on new life as an important tool in spectroscopic analysis and continues to
be applied in an increasing number of fields. The mechanism and sequence steps of the
photoacoustic signal generation process is shown in Fig. 1.1 and Fig1.2.
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Section 1.3
A BRIEF REVIEW OF EARLIER EXPERIMENTAL TECHNIQUES
Photoacoustic Spectroscopy (PAS) works on the photoacoustic effect discussed in
earlier section. Photoacoustic spectroscopy is a new technique recently being used as a
potential tool which finds applications in almost all disciplines of Science and
Technology.
A variety of methods have been employed for the estimation of air pollutants
such as nitrogen oxides27
(NOx), carbon monoxide (CO), carbon soot16
, sulfur oxides
(SOx), carbon dioxide (CO2), volatile organic compounds17
(VOC), particulate matter
(PM) and toxic metals. Traditional methods for estimation of air pollutants are photo-
ionization, IR spectrophotometer, chromatography, gas analyzers etc.. Many of these
methods suffer from interferences, selectivity, sensitivity and dynamic range. They can
be labor intensive and often difficult to automate. Multiple elements can be determined
by adding additional channels to the system. However, this adds complexity and cost to
the instrument.
The analysis of air pollutants is a very difficult task despite the appearance of
new methods. The following are different methods that are in use for the estimation of
air pollutants.
1. Photo-ionization detector
2. Flame ionization detector
3. Infrared spectroscopy
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4. Fourier Transform Infrared analyzer
5. Gas chromatography
6. Metal oxide semiconductor sensors and
7. Aethalometer
Photo-Ionization Detector
Photo-ionization detector is an instrument which is used to detect the volatile organic
contaminants28
(VOCs). It is an efficient detector for many gases and vapor analytes.
High energy light sources typically ultraviolet (UV) range are used to break molecules
into positively charged ions. The targeted gas molecules absorb the energy of UV light
and are ionized, which forms as positively charged ions. The process of ionization is
as follows
RH + hυυυυ RH+ + e-
hυυυυ is a photon energy, which has greater or equal than ionization energy of species RH.
The targeted gas molecules get electrically charged and produce the ions as an electric
current, which is the final output signal of the detector. The greater concentration of the
element produces more current. The output current is amplified and final data presented
on the display. This method is expensive and time-consuming.
Flame Ionization Detector
Flame ionization detector29
(FID) is a powerful analytical instrument which is employed
to detect organic and inorgnic compounds. Hydrogen flame is used as the source of
ionization energy. FID is able to detect nearly all-organic compounds. In clean air, the
hydrogen flame is free from ions and non-conducting. Organic contaminants containing
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either a carbon-hydrogen or carbon-carbon bond break down according to the following
reaction when exposed to the hydrogen flame in the ionization chamber.
RH + O RHO+ + e- + CO2 + H2O
Positively charged carbon containing ions are collected on a negatively charged plate.
The ion current is proportional to the hydrocarbon concentration.
A major difference between FID and PID detection is the amount of variance in
sensitivity from one organic substance to another. The amount of energy (ionization
potential) is necessary to remove an electron to create a charged fragment which
determines the sensitivity of a PID detector to a specific molecule. The shape, size
and specific chemical bonds present within the molecule determine the Ionization
potential (IP). Ionization potential varies widely from one substance to the next. For
these reasons, the sensitivity of a PID detector also varies widely from one substance
to the next.
FID sensitivity does not vary as significantly from one organic substance to
another because the amount of energy necessary to break specific carbon-carbon or
carbon-hydrogen bonds is relatively constant. For this reason FID sensitivity is more
generalized and varies much less significantly between one hydrocarbon and another.
Another very important difference between the two detection techniques is that FID can
detect methane while PID can not detect. FID has traditionally been the preferred
instrument for detection of methane and other saturated alkanes as well as unsaturated
hydrocarbons and alkenes at parts per million levels. Hydroxyl (OH-) or chloride (Cl-)
functional groups tend to reduce sensitivity while inorganic contaminants such as
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chlorine, ammonia and hydrogen cyanide are not detected. FIDs are best for easily
flammable components. However, FID destroys most of components and no further
detection is possible.
Infrared Spectroscopy
Infrared spectroscopy(30,31)
is one of the most powerful analytical techniques, which
offers the possibility of chemical identification. IR technique when coupled with
intensity measurements may be used for quantitative analysis. Infrared spectroscopy has
been of tremendous use to chemists and it is currently more popular as compared to
other physical techniques (X-ray diffraction, electron spin resonance, etc.,) in the
elucidation of the structure of unknown compounds. The infrared radiation refers
broadly to that part of the electromagnetic spectrum which lies between the visible and
microwave regions. The infrared region of the spectrum encompasses radiation with
wave numbers ranging from about 12,800 to 10 cm-1
or wavelengths from 0.78 to 1000
urn. From instrumentation and application point of view, the infrared region has been
subdivided into near IR region32
(overtone region), mid IR region (vibration rotation
region) and far IR region (rotation region). The techniques and the applications of
methods based upon the three infrared spectral regions differ considerably. An infrared
spectrum shows downward peaks corresponding to absorption, plotted against
wavelength (λ) or wave number (ϋ). In the infrared spectrum, apart from the prominent
modes of vibrations, there are other vibrations due to coupling and overtones that may
lead to additional bands in the spectrum.
The various bands can be interpreted according to the characteristics functional groups
present in the compound. Infrared absorption, emission and reflection spectra for
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molecular species can be rationalized by assuming that they all arise from various
changes in energy state brought about by transitions of molecules from one vibrational
or rotational energy state to another.
Absorption of infrared radiation is thus confined largely to molecular species
that have small energy differences between various vibrational and rotational states. In
order to absorb infrared radiation, a molecule must undergo a net change in dipole
moment as a consequence of its vibrational or rotational motion. Only under these
circumstances can an alternating electrical field of the radiation interact with the
molecule and cause changes in the amplitude of one of its motions.
The basic components of an infrared spectrometer are radiation source,
monochromator, detector, amplifier and recorder. A radiation source provides radiation
over the entire range of the infrared spectrum. The monochromator disperses33
the light
and then selects a narrow wave number range. The detector measures the energy and
transforms it into an electric signal. This signal is further amplified and registered by the
recorder. The IR spectra of most of the contaminant air samples were recorded in mid
and far IR region and are used for the investigation. Typical applications of IR
spectrometer include monitoring for the presence of anesthetic gases and organic
solvents such as nitrous oxide, nitrogen dioxide, halothane, toluene, carbon dioxide,
carbon monoxide as well as many other organic compounds. This method consumes
time for sample preparation and it cannot give information in detailed.
Fourier Transform Infrared Spectroscopy
Fourier transform infrared (FTIR) spectroscopy is a technique which is used to obtain
an infrared spectrum of absorption and emission of a liquid or gas. FTIR spectrometer
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simultaneously collects spectral data in a wide spectral range. The fourier transform
infrared34
spectrograph have replaced the conventional infrared spectrograph. A FT-
Infrared spectrometer consists of two parts: (a) An optical system, which uses an
interferometer and (b) A dedicated computer which stores data, performs computations
on data and plots the spectra. It consists of two perpendicular mirrors; one of which is a
stationary mirror and other a movable mirror which can be displaced perpendicularly to
the fixed mirror at a constant velocity. Between these two mirrors is beam splitter set at
45° from the initial position of the movable mirror. A parallel beam of radiation from an
infrared source is passed to the mirrors through the beam splitter. The beam splitter
reflects about half of the beam to the fixed mirror, which reflects it back to the beam
splitter and transmits the other half to the movable mirror, which reflects it back to the
beam splitter. The returning beams are again split and mixed about half going back to
source and half passing through the sample compartment. The composition of the beam
splitter depends on the spectral region of interest. For example in the mid-infrared
region (4000-400 cm-1
), a beam splitter of germanium coated on KBr plate (substrate) is
often used. Germanium reflects the radiation while Kbr transmits most of the desirable
radiation. In the far infrared region, germanium coated on CSI (800-200 cm-1
) or
germanium coated on Mylar (polyethylene terephthalete) (650-10 cm-1
) are used as
beam splitters. A thin film of the beam splitter material is coated on an optically flat
substrate. The return beams from both the mirrors along the same path length as their
incident path are recombined into a single beam at the beam splitter. The path length of
one of the return beams is changed in order to create phase difference to cause an
interference pattern. The recombined radiation is then directed through the sample and
focused on to the detector. The detector measures the amount of energy at discrete
intervals of mirror movement. The movable mirror can be moved in a range of say ± 5
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cm. The mirror velocities from 0.05 to 5 cm-1
are used. Interferometer instruments need
detectors with response times short enough to detect and transmit rapid changes to the
recorder. The detector used in conjunction with rapid scanning interferometers in the
mid-infrared region is triglycine sulfate with KBr windows as pyroelectric bolometer. It
has a high response time. Other most common detectors used such as thermocouples,
bolometers and Golay detectors which have short response time. This method is not
suitable to measure spectra. It measures interferogram only.
Gas Chromatography
Gas chromatography
35 is a method for separating the components of a gas or liquid and
measuring their relative quantities. It is a useful technique for chemicals that do not
decompose at high temperatures and when a very small quantity of sample is available.
The use of gas chromatography is limited by the decomposition temperature of the
components of the mixture and the composition of the column. Most columns cannot
withstand temperatures greater than 250-350°C.
In gas chromatography, a sample is rapidly heated and vaporized at the injection
port. The sample is transported through the column by a mobile phase consisting of an
inert gas. Sample components are separated based on their boiling points and relative
affinity for the stationary phase, which is most often a viscous liquid within the column.
The higher a components affinity for the stationary phase, the slower it comes off the
column. The components are then detected and represented as peaks on a
chromatogram. This method is time taking. Also, it is difficult to measure and inject
such small samples (approx 0.3microlitres) accurately without evaporation of the
sample.
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Metal oxide semiconductor sensors
Metal Oxide Semiconductor36
(MOS) sensors are application specific gas sensors which
use metal oxide based sensing thick films deposited onto a Si-micro-machined
substrate. The substrate contains electrodes which measure the resistance of the sensing
layer, and a heater that heats the sensing layer from 200°C to 400°C. The sensor
responds to changes in the composition of the ambient atmosphere with a change in the
resistance of the sensing layer. A large number of toxic and explosive gases can be
detected even at very low concentrations. MOS sensors detect a wide range of gases
such as carbon monoxide (CO), nitrogen oxides (NO2), ammonia (NH3), hydrogen
sulfide (H2S), methane (CH4) and a wide variety of volatile organic compounds
(VOCs).
The working principle of the MOS is the changes in composition of the ambient
atmosphere will determine changes in resistance of the sensing layers. In practice, the
relationship between sensor resistance and concentration of the target gas usually
follows a power law. Over a large range of concentrations, it can be described as
follows
R= Kc+n
R is the resistance of the sensing layer, c is the concentration of the target gas, K is a
measurement constant and n has values between 0.3 and 0.8. The positive sign of n is
used for oxidizing gases and the negative sign for reducing gases.
MOS sensors have been used extensively to measure and monitor trace amounts
of environmentally important gases such as carbon monoxide and nitrogen dioxide.
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They are susceptible to humidity which cause drift on analysis. Low stability and long
range drift are important issue in this method.
Aethalometer
The aethalometer is an instrument which offers a real-time readout of the concentration
of black or elemental carbon particles in the air stream. The carbon particles emit from
all types of combustion most notably from diesel engine exhaust. The aethalometer uses
a continuous filtration and optical measurement method to give a continuous readout of
real-time data. It contains a sampling port that may be preceded by size-selective inlet
for the measurement of elemental particles in a specified aerodynamic size fraction.
The optical measurement method for black carbon is consistent and
reproducible. A wide body of published research shows that the aethalometer black
carbon measurement is closely proportional to filter-based elemental carbon
measurements. The aethalometer performs the optical analysis and data readout on-site.
However, this method is expensive and time consuming.
In the present system, a simple, significant photoacoustic cell, novel
acoustic detectors and 32-bit microcontroller based system for the measurement of air
pollutants are designed and developed. Photoacoustic is direct technique for trace gas
analysis. It is novel in the sense of low-level concentrations while most of the existing
techniques such as conventional and indirect methods. This technique plays an
important role in increase signal to noise ratio and plays significant role in
instrumentation.
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Section 1.4
ROLE OF EMBEDDED SYSTEMS IN INSTRUMENTATION
Instrumentation(37-38)
is a technology of measurement and control which serves not only
science but also all branches of engineering, medicine and etc. Now a days embedded
system is a very powerful tool in instrumentation (measurement and control) systems.
The advanced embedded based measurement is fast, highly reliable, precise, accurate
and all flexible to make it perfectly for any given task. An embedded system is a
computing system that is embedded inside of a product, for example a computing
system is dedicated to controlling some non-computing hardware like washing machine,
a car engine or a missile. Computing machines were always the attraction for fast
development of science and technology in the field of automation for industrial and
domestic products. Automation being one of the objectives, the computational needs
was the motivation for the development of computing machines and devices. The
computing system is part of procedure or process. The most important component in an
embedded system is the microprocessor or microcontroller.
Microcontroller
39 is an electronic single chip microcomputer that is more
suited for measurement and control of instruments. Microcontroller has been treated as
a tool for computing and communication with other devices. Knowledge of
microcontrollers is meaningful and very rewarding if it is applied to design a product
that is useful in the industry or for the society in general. Microcontrollers are more
suited for control and automation of process, analytical, biomedical industries and etc.
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There are two types of architectures available namely, Harvard architecture and Von
Neumann architecture.
Harvard architecture
Harvard architecture uses separate memories for program and data with their
independent address and data buses. Because of two different streams of data and
address, there is no need to have any time division multiplexing of address and data
buses. The more designs of microcontrollers are followed by Harvard architecture. Not
only the architecture supports parallel buses for address and data, but also it allows a
different internal organization such that instruction can be pre-fetched and decoded
while multiple data are being fetched and operated on. Further, the data bus may have
different size than the address bus. This allows the optimal bus widths of the data and
address buses for fast execution of the instruction. The examples of Harvard
architecture are MCS-51 from Intel corporation and PIC from Microchip.
Von Neumann Architecture
In Von Neumann architecture, program and data share the same memory space. Von
Neumann architecture allows storing or modifying the programs easily. However, the
code storage may not be optional and requires multiple fetches to form the instruction.
Program and data fetches are done using time division multiplexing which affect the
performance. The example of Von Neumann architecture is 68HC11 from Motorola.
An embedded system can be defined as a computing device that does a specific
focused job. Appliances such as the air-conditioner, VCD player, DVD player, printer,
fax machine, mobile phone etc. are example of embedded systems. Each of these
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appliances will have a processor and special hardware to meet the specific requirement
of the application along with the embedded software that is executed by the processor
for meeting that specific requirement. The embedded software40
is also called firmware.
The desktop/laptop computer is a general-purpose computer. We can use it for a variety
of applications such as playing games, word processing, accounting, software
development and so on. In contrast, the software in the embedded systems are always
fixed. Some of special features are listed below
Embedded systems do a very specific task.
Embedded systems have limited resources that have particularly in the memory.
A specific job has to be completed within a specific time. In some embedded
systems is called real-time systems.
Embedded systems consume very low power. Many embedded systems have
been operating thorough a battery power.
Embedded systems are highly reliable.
Some of embedded systems operate in extreme environmental conditions such
as very high temperatures and humidity.
More embedded systems are addressed to the consumer market for example,
electronic toys, mobile phones, home appliances etc.
The embedded system market is one of the highest growing areas as these
systems are used in consumer electronics, office automation, industrial automation,
biomedical engineering, wireless communication, data communication,
telecommunication, transportation, military etc.
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Areas of Embedded systems
1. Consumer appliances
At home we use a number of embedded systems, which include digital camera, digital
dairy, DVD player, electronic toys, microwave oven, remote controls for TV and air-
conditioner, VCD player, video game consoles, video recorders etc. Today’s high-tech
car has about 20 embedded systems for transmission control, engine spark control, air-
conditioning, navigation etc. Even wristwatches are now becoming embedded systems.
The palmtops are powerful embedded systems using which we can carry out many
general-purpose takes such as playing games and word processing.
2. Office automation
The office automation products using embedded systems are copying machine, fax
machine, key telephone, modem, printer, scanner etc.
3. Industrial automation
A lot of industries use embedded systems for process control. These include
pharmaceutical, cement, sugar, oil exploration, nuclear energy, electricity generation
and transmission. The embedded systems for industrial use are designed to carry out
specific tasks such as monitoring the temperature, pressure, humidity, voltage, current
etc., and then take appropriate action based on the monitored levels to control other
devices or to send information to a centralized monitoring station. In hazardous
industrial environment, where human presence has to be avoided, robots are used,
which are programmed to do specific jobs. The robots are now becoming very powerful
and carry out many interesting and complicated tasks such as hardware assembly.
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4. Medical electronics
Almost all medical equipments in the hospital are an embedded system. These
equipments include diagnostic aids such as ECG, EEG, blood pressure measuring
devices, X-ray scanners; equipment used in blood analysis, radiation, colonoscopy,
endoscopy etc. Developments in medical electronics have paved way for more accurate
diagnosis of diseases.
5. Computer networking
Computer networking products such as bridges, routers, Integrated Services Digital
Networks (ISDN), Asynchronous Transfer Mode (ATM) and frame relay switches are
developed with embedded systems, which are implemented to the necessary data
communication protocols. A router interconnects two networks, which may be running
different protocol stacks. The router’s function is obtain the data packets from incoming
ports, analyze the packets and sends them towards the destination after doing necessary
protocol conversion. Most networking equipments, other than the end-systems (desktop
computers) we use to access the networks, are embedded systems.
6. Telecommunications
In the field of telecommunications, the embedded systems can be categorized as
subscriber terminals and network equipment. The subscriber terminals such as key
telephones, ISDN phones, terminal adapters, web cameras are embedded systems. The
network equipment includes multiplexer, multiple access systems, Packet Assemblers
Disassembers (PADs), satellite modems etc. IP phone, IP gateway, IP gatekeeper etc. are
the latest embedded systems that provide very low-cost voice communication over the
Internet.
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7. Wireless technologies
Advantages in mobile communications are paving way for many interesting
applications using embedded systems. The mobile phone is one of the marvels of the
last decade of the 20th century. It is a very powerful embedded system that provides
voice communication while we are on the move. The personal Digital Assistants and the
palmtops can now be used to access multimedia services over the Internet. Mobile
communication infrastructure such as base station controllers, mobile switching centers
are powerful embedded systems.
8. Instrumentation
Testing, measurement and controlling are the fundamental requirements in all scientific
and engineering activities. The measuring equipment in laboratories are used to measure
the physical parameters such as weight, temperature, pressure, humidity, voltage,
current etc. The test equipments such as oscilloscope, spectrum analyzer, protocol
analyzer, radio communication test set etc. are developed with the embedded systems.
9. Security
Security of persons and information has been a major issue. We need to protect the
information, transmit and also store the data. Developing embedded systems for security
applications is one of the most profitable businesses nowadays. Security devices at
homes, offices, airports and authentication are developed using embedded systems.
Encryption devices are used to encrypt the data/voice being transmitted on
communication links such as telephone lines. Biometric systems using
fingerprintandface recognition are now being extensively used for user authentication in
banking applications as well as for access control in high security buildings.
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10. Finance
Financial dealing through cash and cheques are now slowly paving way for transactions
using smart cards and ATM (Automatic Teller Machine) machines. Smart cards and
credit card have a small microcontroller and extra memory and also it interacts with the
smart card reader/ATM machine and acts as an electronic wallet. Smart card technology
has the capability of ushering in cashless society.
Recent trends in embedded systems
Most of the embedded software was written only in assembly language and hence
writing, debugging and maintaining the code were very different and time consuming.
With the availability of powerful processors and advanced development tools,
embedded software development is no longer ‘rocket science’.
(i) Processor
The growing importance of embedded systems can be gauged by the availability of
processors. Powerful 8-bit, 16-bit, 32-bit and 64-bit microprocessors and
microcontrollers are available to provide the different market segments. The clock speed
and the memory addressing capability of the processor are also increased. Very
powerful digital signal processors are also available for real-time analysis of audio and
video signal.
(ii) Memory
The cost of memory chips is reducing day by day. As a result, the embedded systems
can be made functionally rich by incorporating additional features such as networking
protocols and even graphical user interface. The cost of memory chips used to
discourage developers from porting an operating system onto target hardware. As the
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memory chips are becoming cheaper, porting an operating system is no longer an issue.
Now, wristwatches with embedded Linux operating system are available.
(iii) Operating system
A variety of operating systems are available which can be ported onto the embedded
system. The main advantage of embedding on operating system is that the software
development to be very fast, multitasking and maintaining the code is very easy. The
software can be developed in a high-level language such as C and C++. Linux operating
system is available as an open source in Internet. It is very useful to an embedded
systems and real time operating system applications. The complete source code is also
available for specific application. Just we can customize the software as per our
application needs.
(iv) Programming languages
Development of embedded systems software was mostly in assembly language.
However due to the availability of cross-compilers, most of the developers are done in
high level languages such as C and C++. The object-oriented languages like VC++, C++
and Java are catching up for more applications now. The main attraction of java
language is the platform independence. In fact, the development of java programming
languages was initiated mainly to address the embedded systems market.
(v) Development Tools
Availability of a number of tools for development, debugging and testing as well as for
modeling the embedded systems is now paving way for fast development of robust and
reliable systems. Development tools such as KEIL, RIDE, MATLAB and simulink can
be used to model embedded systems as well as to generate code, substantially reducing
the development time.
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(vi) Programmable devices
Programmable logic device (PLDs) and field program beal gate arrays (FPGAs) pave
the way for reducing the components on embedded systems, leading to small, low-cost
systems. After developing the prototype of embedded systems, for mass production, the
FPGA can be developed which will have all the functionality of the processor,
peripherals as well as the application-specific circuitry. Systems-on-chip is the
catchword that reflects the current developments of programmable hardware in a single
chip embedded systems.
Applications
In our lives we come across many devices having a certain amount of intelligence
embedded systems that include automobiles, communications, military, medical,
consumer, entertainment appliances and personal digital assistances. In desktop
computers, we can find out more applications using microcontrollers such as keyboard,
modems, printers and other peripherals. In test equipment, microcontrollers make it
easy to add futures such as the display, store the data and display messages as well as
graphs. In consumer products the microcontrollers are essential inside of cameras, video
records, disk players and ovens. Embedded systems are playing a major role in
mentioned below fields
Analytical Instrumentation
Aeronautical Instrumentation
Bio-medical Instrumentation
Electronic Instrumentation
Industrial Instrumentation
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Laser Instrumentation
Optical Instrumentation
Process Instrumentation etc.
Embedded system41
plays a pivotal role in instrumentation. The interfacing
of instruments with microcontroller has vastly increased our ability to measure and
compact in size. The attempt to design and develop of embedded based systems for the
measurement is rather scarce particularly in India though they offer many advantages.
Hence, the need to design and develop of embedded based system for measurement. In
the present study, an embedded based photoacoustic system is developed for the
measurement of air pollutants in industrial and automobile emissions.
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Section 1.5
PURPOSE AND SCOPE OF THE PRESENT STUDY
Nowadays, air pollution is presented as a serious threat to the planet. The concentration
of gases from anthropogenic activities such as transport, cause consequences ranging
from local to global scale, effecting the climate, the environment and the human health.
It is necessary to detect and monitor of a large number of gas species emitted by these
source of pollutants. The photothermal techniques, specially photoacoustic
spectroscopy, allow the detection of many gaseous species. The estimation of air
pollutants such as nitrogen dioxide, carbon monoxide and carbon soot concentrations in
industrial and automobile emissions give valuable information to ecologists,
agriculturists, chemists, biochemists etc. The excess of these elements causes severe
health disorders in human beings, animals and plants. It is necessary to analyze these air
pollutants and to take necessary precautions. The measurements of concentration of
these pollutants are very essential to warn and educate the people on its toxic effects in
the corresponding fields.
Modern measuring instruments are the fruits of science and technology. New
discoveries in science provided new instruments for the study of nature and matter. The
precise and accurate measurement of physical and chemical parameters plays an
important role in unraveling the mysteries of nature.
No doubt, several investigators developed the techniques for the measurement of
air pollutants concentration in different samples and several manufacturers are
producing a variety of instruments for different pollutant estimation. But these are
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conventional, indirect and suffer from many disadvantages. But the attempts to design
and develop the embedded based systems for the measurement of air pollutants are
rather scarce particularly in India though they offer many advantages. Hence, in the
present study, an attempt is made to design and development of embedded based
systems for measurement of air pollutants in industrial and automobile emissions.
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REFERENCES
1. A Aaron Daly and P Zannetti “An Introduction to Air Pollution-Definitions,
Classifications and History”, Published by The EnviroComp Institute, USA(2007).
2. Alan Robock, Reviews of Geophysics, 38, 191(2000).
3. A Marley Nancy and S Jeffrey Gaffney, “ New improved fast GC-Luminol
Instrument for PAN and nitrogen dioxide measurements”, Environmental Research
Division Argonne National Laboratory, USA (2004).
4. Shinichi Komato and Keizo Kobayachi, Journal of Atmospheric Environment,
24, 1535 (1990).
5. M V L R Anjaneyulu., M Harikrishna and S Chenchuobulu, Journal of World
Academy of Science, Engineering and Technology,17, 135 (2008).
6. Ming Zheng, Graham Reader and J Gary Hawley, 45, 883 (2004).
7. Health effects of air pollutants (website: www.vtpi.org/tca/tca0510.pdf)
8. Handbook of Pollution Prevention and Abatement, World Bank Group, Canada
(1998).
9. Richa Rai, Madhu Rajput, Madhoolika and Agrawal, Journal of Scientific Research,
55, 48 (2011).
10. Mohsen Mehrara and Hossein Amiri, Journal of Social and Development Sciences,
2, 233(2011).
11. Kyung Hwan Kim, Kazuhiko Sekiguchi and Shinji Kudo, Journal of Aerosol and Air
Quality Research, 11, 1(2011).
12. Understanding Particulate Matter (Website:www.iowa.sierraclub.org/ AirQuality/
BlackCarbon.pdf).
13. Letizia DeMaria and Giuseppe Rizzi, Journal of Sensors, 2009, 1-5(2009).
14. Ozone pollutant (www.arb.ca.gov/research/aaqs/caaqs/ozone/ozone-fs.pdf).
15. Dimari, G S Hati and Waziri, European Journal of Scientific Research, 23, 465
(2008).
16. Terumi Tanimoto and Akira Hoshika, Journal of Oceanography, 53, 365 (1997).
17. Particulate matter pollution from Maryland Power Plants, Environment
Maryland Research & Policy Center, USA (2007).
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18. P. Eugene, Journal of Environmental Economics and Management, 10, 112 (1983).
19. Sirajuddin Horaginamani, M Ravichandran, Journal of Science, Engineering and
Technology, 6, 13 (2010).
20. C. Haisch and R. Niassner, Spectroscopy Europe, 14, 11 (2002).
21. Alexander Graham Bell, American Journal of Science, 20, 305 (1880).
22. A. G. Bell, Philosophical Magazine, 11, 510 (1881).
23. Allan Rosencwaig and Allen Gersho, Journal of Applied Physics, 47, 64, (1976).
24. J. M. Frans Harren, Gina Cotti, Jos Oomens and Sacco Hekkert, Enclopedia of
Analytical Chemistry,2, 2203 (2006).
25. H A Beck, R Niessner, C Haisch, Anal. Bioanal. Chem 375, 1136 (2003).
26. Mark Jacobson, Journal of Geophysical Research, 115, 34 (2010).
27. A Nancy Marley and S Jeffrey Gaffney, “New Improved Fast GC-Luminol
Instrument for PAN and Nitrogen Dioxide Measurements”, Environmental
Research Division Argonne National Laboratory, Argonne, USA(1999)
28. A. H. Goldstein and I E Galbally, Environmental Science & Technology, 51, 1515
(2007).
29. Mc William and Dewar, “Flame Ionization Detector for Gas Chromatography”,
Nature Publishing Grop, 181, 760(1958).
30. C. P. Sherman Hsu, Handbook of Instrumental Techniques for Analytical Chemistry,
“Infrared Spectroscopy”, Separation Science (2001).
31. R. W. Jones and J F Mcclelland, Journal of Spectroscopy, 7, 54 (1992).
32. D. R. Griffin, R Hubbard and G Wald.Journal of Optical Society of America, 37,
29 (1947).
33. Website: http://www.shsu.edu/~chm_tgc/primers/pdf/mono.pdf.
34. W. Xie and W. P. Pan, Journal of Thermal Analysis and Calorimetry, 65, 669
(2001).
35. Chunxiao Wang, “Simultaneous Analysis of Greenhouse Gases by Gas
Chromatography”, Application Note, Agilent Technologies (1998).
36. George Fine, Leon Cavanagh, Ayo Afonja and Russell Binions, Journal of
Sensors, 10, 5469 (2010).
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37. B. C. Nakra, K Chaudhary, “Instrumentation Measurement and Analysis”, Tata
McGraw-Hill Publishers, New Delhi (1995).
38. C. S. Rangan, G R Sharma and V S V Mani , “Instrumentation Devices and
Systems”, 2nd
Edition, Tata McGraw-Hill Publishers, New Delhi (2002).
39. Ajay Deshmukh,“ Microcontrollers theory and Applications”, Eight reprint, Tata
McGraw-Hill Publishers, New Delhi (2008).
40. K.V.K. Prasad, “Embedded/Real systems: Concepts, Design and Programming”,
Black Book, Reprint Edition, Published by Dreamtech Press, New Delhi (2007).
41. Raj Kamal, “ Embedded Systems”, Tata McGraw-Hill Publishers, New Delhi
(2003).
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CHAPTER 2
Design and Development of Embedded
Based Photoacoustic Measurement
System - Hardware Design
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Section 2.1
PRINCIPLE
In the present study, an embedded based photoacoustic system is designed and
developed. It works on the principle of photoacoustic effect1. The photoacoustic effect
is shown in Fig. 2.1. The embedded based photoacoustic system consists of a laser as
radiation source, a photoacoustic resonant cell as acoustic signal generator, acoustic
detector and the pollutant air whose pollutant concentration is to be estimated. The
photoacoustic cell2 generates the acoustic waves proportional to the concentration of the
air pollutant. The acoustic detector produces a voltage proportional to the acoustic
waves. The voltage produced is in the order of micro volts.
Different types of modulated laser sources are used as a exciting sources
corresponding to the air pollutant to be detected. These lasers offers high spectral
brightness and narrow spectral line widths. A square wave of function generator is used
to modulate the laser source at fixed frequency. The XR2206 is a function generator
chip. It acts as a square wave generator which is used to modulate the laser as well as
reference to the lock-in amplifier. The lock-in amplifier is a narrow bandpass filter and
amplifier which is used to measure very low level signal of about nano-volt (nV)
amplitude obscured by noise.
The voltage produced in the acoustic detector is given to a low noise
preamplifier of lock-in amplifier and the output of the lock-in amplifier in converted
into digital form with the help of an analog to digital converter. The embedded system is
used to acquire, process
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and display the digital information corresponding to the air pollutant concentration with
appropriate interfacing devices. The necessary software to operate the system is
developed in embedded C language.
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Section 2.2
FUNCTIOINAL BLOCK DIAGRAM
The functional block diagram of embedded based photoacoustic system for the
measurement of air pollutants is shown in Fig. 2.2. The block diagram consists of the
following different functional modules and sub-modules.
4. Radiation source
5. Modulator for radiation source
6. Photoacoustic cell
7. Acoustic detector
8. Low noise Pre-amplifier
9. Lock-in amplifier
10. Temperature sensing unit
11. Pressure sensing unit
12. Data acquisition system
13. ARM 32-bit microcontroller
14. LCD display
15. Power supply unit
16. Sample handling system
Each individual functional module is designed and implemented in the present study.
The details are presented in this chapter.
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Section 2.3
RADIATION SOURCE
The two categories of radiation sources are used for photoacoustic studies3. The first
category has broad wavelength radiation sources such as arc lamps, halogen tungsten,
filaments, glowbar sources etc. which have low spectral brightness, incapability of fast
modulation and necessitate the use of external selective elements like prism or grating to
get tunable wavelength output. The second category has narrow wavelength radiation
sources such as lasers or monochromatic light sources. The advantages of laser sources
are high spectral brightness, narrow spectral line widths and intra or extra cavity
modulation. The different lasers such as solid state lasers, gas lasers and dye lasers are
developed and which are available in the market for scientific studies.
In present study, diode pumped solid-state (DPSS) lasers SDL-532, SLD-870
and SLD-1600 are used for the detection of nitrogen oxides, carbon soot and carbon
monoxide pollutants in industrial and automobile emissions. The lasers are obtained
from Dream lasers technologies limited, China. The diode pumped solid-state lasers are
solid state lasers which are made by pumping a solid gain medium with a diode laser.
They offer compactness, efficiency over other types and high power. The specifications
of DPSS laser sources are shown in Table 2.1(a), Table 2.1(b) and Table 2.1(c).
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Table 2.1(a): Technical specifications of diode pumped solid state laser SDL-532
Table 2.1(b) : Technical specifications of diode pumped solid state laser SDL-870
S. No Parameter Value
1 Wavelength 870nm±1
2 Output power 20Mw
3 Operation mode CW
4 Modulation (TTL/Analog) frequency
range
0-5kHz
5 Operating temperature 5-50o C
6 Expect life time 10000 hours
S. No Parameter Value
1 Wavelength 532nm±1
2 Output power 20mW
3 Operation mode CW
4 Be Beam diameter 2mm
5 Beam roundness >95%
6 Modulation (TTL/Analog) frequency
range
0-5kHz
7 Operating temperature 5-50o C
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Table 2.1(c) : Technical specifications of diode pumped solid state laser SDL-1600
S. No Parameter Value
1 Wavelength 1600nm±5
2 Output power 10mW
3 Operation mode CW
4 Modulation (TTL/Analog) frequency
range
0-5kHz
5 Operating temperature 5-50o C
6 Expect life time 10000 hours
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Section 2.4
MODUALTOR FOR RADIATION SOURCE
It is necessary to modulate the laser beam for photoacoustic measurements. The various
techniques are used to modulate the laser sources which are described in detail in this
section. The suitable technique for modulation is essential to modulate the laser
accurately. The modulating techniques such as Q-switching, pulsating flash lamp,
frequency modulation, amplitude modulation, electro-optic modulation and mechanical
modulation have been used in photoacoustic studies. In those techniques, the amplitude
modulation technique is the most popular and suitable technique to use in present study.
The amplitude modulation techniques are commonly used in two ways which are briefly
described as follows.
(i) Mechanical amplitude modulation
Mechanical amplitude modulation is one of the techniques used in photoacoustic
measurement system which is generally called as mechanical chopper. The mechanical
chopper consists of a slotted disk and DC motor which places in the path of light beam.
It chops the light beam in form of 50% duty cycle. The chopper offers 100% modulation
within a range of frequency from few Hz to 500Hz only. The disadvantage of the
mechanical chopper is mechanical vibrations take place at higher frequencies (kHz) and
sound noise associate with the fast rotating blades.
(ii) Electronic amplitude modulation
The electronic amplitude modulation is one of the simple modulating techniques. It
operates a range of frequency from few Hz to MHz. The signal of function generator is
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used to modulate the laser source in the present study. The function generator is a signal
generator which is used to modulate the laser source. The XR-2206 is a monolithic
function generator which produces high quality sine, square, triangle, ramp and pulse
waveforms. The output waveforms have high stability and good accuracy. The function
generator XR-2206 operates a range of frequency from 0.01Hz to 1MHz. The frequency
of operation can be selected by simple external resistor and capacitor. The salient
features of XR-2206 function generator are as follows
4. Sine wave distortion typically 0.5%
5. Temperature stability 20ppm/°C
6. Linear amplitude modulation
7. TTL Compatibility
8. Wide supply range
9. Adjustable duty cycle from 1% to 99%
The frequency of oscillator (Fo) of function generator is determined by the external
timing capacitor C and resistor R. The capacitor is connected across pin 5 & 6 and the
timing resistor is connected across pin 7&8 of function generator XR 2206 which are
shown in the circuit diagram. The output signal frequency of function generator XR
2206 is calculated as follows
Frequency, Fo = 1/ RC Hz
= 1/ 4.87K x 0.1µF
= 2.053 kHz
The signal frequency of function generator can be adjusted by varying a variable
resistor. The circuit diagram of square wave generator is shown in the Fig. 2.3. The
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generated square wave of function generator XR22064 is used to modulate the diode
pumped solid state (DPSS) laser source. The modulated laser beam is applied to
generate the photoacoustic signal in the present study.
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Section 2.5
PHOTOACOUSTIC CELL
The photoacoustic (PA) cell5 serves as a container for the sample. It is the heart of
photoacoustic spectrometer which is carefully designed and fabricated in present study.
The design of the PA cell depends on the nature of sample to be studied. A typical PA
cell should have the following characteristics
Proper acoustic shielding is required from ambient atmosphere.
Minimized unwanted signals due to interaction of the excitation light with cell
walls, windows and acoustic detectors or microphones.
Properly configured and placement microphones, sample inlet and outlet.
Increase the signal to noise ratio.
Two types of photoacoustic cells are used in photoacoustic studies which are as
follows
1. Resonant photoacoustic cell
2. Non-resonant photoacoustic cell
Resonant photoacoustic cell
The resonant photoacoustic cell is used to enhance the photoacoustic signal and signal
to noise ratio. The resonant6 frequency depends both on the shape of the resonator and
velocity of sound of the gas sample. The advantages of resonant photoacoustic cell are
simple to increase PA signal and eliminate unwanted signals. The different types of
acoustic resonant cells are shown in Fig. 2.4.
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Table 2.2 : Types of acoustic resonators
S. No Name of acoustic resonator Mode of operation
1 Simple pipe Longitudinal
2 Pipe with two buffer volumes Longitudinal
3 Helmholz resonator Longitudinal
4 Coaxial resonator Radial
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The acoustic noise creates a major problem in single cavity acoustic resonant
cell. The single cavity resonator is not sufficient to suppress the spurious noise. For this
reason, a differential or dual cavity7 (dual pipe with buffers) acoustic resonant cell is
designed and constructed in present study which can suppress back ground noise, flow
fluctuations and gives a relatively noise free photoacoustic signal. The differential
photoacoustic resonant cell is shown in Fig. 2.4(a) & 2.4(b). It consists of two copper
tubes, microphones, acoustic buffers and optical windows. The inner surface of copper
tubes polished and gold plated which can reduce the absorption of incident laser beam
and also withstand corrosion samples. The miniature microphones are sealed in PVC
holders and mounted centrally onto the sides of each tube which are well isolated
acoustically from the surroundings. The copper tubes are placed centrally in a aluminum
enclosure which has 120mm of length and 10mm of wall thickness. Each of the copper
tubes opens into a bigger acoustic buffer such as 50mm of length and 60mm of diameter
on either side. The volume of acoustic buffer is much larger than the cavities. The
acoustic buffers are used to reduce the window absorption noise, detector noise and
turbulence flow of a gas. The acoustic buffers consist of inlet port and outlet port. The
needle valve is used in the inlet line for controlling the flow of inlet gas sample. The
optical windows (BK7) are fixed to the both sides of acoustic buffers which are good in
quality and transmission of light. The dimensions of glass windows are 12.5mm of
diameter and 3mm of thickness which allow the wavelengths of visible region such as
380nm to 800nm. The glass windows are fixed with silicon ‘O’ rings and sealed tightly.
The enclosure of the resonant cell is made-up of aluminum material. The resonant cell is
mounted on a chassis which has a size of 500mm in length, 300mm in
width and 4mm in thickness which is shown in Fig.2.4(c). Finally, the resonant cell is
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tested at its resonant frequency.
Characteristics of the photoacoustic resonant cell
The photoacoustic resonant cell characteristics are quite important in photoacoustic
measurements which depend on its acoustic resonant mode. The characteristics of the
photoacoustic resonant cell are enhancement of the PA signal, noise suppression and
increases signal to noise ratio, which are necessary to study the response of PA resonant
cell. Photoacoustic resonant cell is operated in longitudinal mode in present study.
In longitudinal mode8, the resonant frequency depends on the length and inner
diameter of copper tube, density and viscosity of the gas sample. The acoustic resonant
characteristics of the PA resonant cell are determined with air sample at atmospheric
pressure. A simple loud speaker kept close to one of the windows of the PA resonant cell
and the frequency is applied to the loud speaker from function generator, which is tuned
within a range of frequency from 100 to 4000Hz. The acoustic detector obtained the
signal and normalized against the amplitude of the audio signal being applied. The
fundamental and the first harmonic of the resonant frequencies are clearly seen with the
slight variations induced by the influence of other aspects such as buffer volume and
resonator cavity in the PA cell. Sub-resonant frequencies are shown before the
fundamental resonant frequency, but they are weaker than fundamental resonant
frequency.
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Construction and working
A differential photoacoustic resonator is designed and constructed for the measurement9
of air pollutants in the present study. A differential acoustic resonator is a proper
solution of background noise, windows noise and flow fluctuations which contains two
acoustic resonators, one is signal sensitive resonator and another is reference resonator.
The signal sensitive resonator detects the actual acoustic signal and reference resonator
detects the photoacoustic background signal, windows noise and flow fluctuations. The
two longitudinal resonator tubes are placed in parallel and near to each other. The
resonator tubes are made of copper and polished with gold coating. They contain
excellent heat-conducting properties that absorb heat quickly and disperse in the copper
tube. The gold coating has been served not only to optimize the reflection of laser
radiation, but also to obtain a noncorrosive surface to withstand aggressive gases. The
two miniature professional microphones are equipped in acoustic resonators. An end of
acoustic resonators are opened and coupled with acoustic buffers. The acoustic buffers
are made of stainless steel which can withstand with corrosive gases which minimize
the acoustic noises such as background noise and inlet/outlet flow fluctuations.
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Table 2.3 : Specifications of differential photoacoustic resonant cell
S. No Name of Parameter Designed value
1 Resonator length 80mm
2 Resonator diameter 5mm
3 Buffer length 50mm
4 Buffer diameter 60mm
5 Resonant frequency 2085 Hz
6 Quality factor 21 + 0.5
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The resonant frequency and quality factor of acoustic resonator are expressed as
Resonant frequency, Fres = NC / 2(L+∆l) -------- (1), N= 1,2,3,4,5…
= 340 / 2(0.08+0.0015)
= 2085 Hz at 20 deg C
Quality factor (Q) = Fres / ∆f = ~ 21 -------- (2)
Where C is the velocity of sound in air, N is the acoustic longitudinal modes in
cylindrical resonator, L is the length of the resonant tube, ∆∆∆∆l is an end correction factor
and ∆∆∆∆f is the full width half maximum of resonant frequency. The theoretical resonator
frequency can be calculated as per equation (1) and expressed, but practical resonant
frequency is found at 2055Hz. A small variation is occurred due to made up of small
holes on resonators for acoustic detectors. The resonant frequency of photoacoustic
resonant cell is tested with a loud speaker which is explained in detail in chapter 4.
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Section 2.6
ACOUSTIC DETECTOR
Acoustic detector or microphone is a transducer which is used to convert acoustic wave
into an electrical signal. The microphones use capacitance change to produce an
electrical voltage from mechanical vibration. The diaphragm of microphone acts as one
plate of a capacitor and the vibrations produce changes in the distance between the
plates. The constant DC voltage is applied to the microphone plates that the plates are
biased with a fixed charge (Q). The voltage (V) maintains across the capacitor plates
changes with the vibrations in the air according to the capacitance. The charging
capacity is given as
C = Q/V
Where Q is charge in coulombs, C is capacitance in farads and V is potential difference
in volts. The capacitance of the plates is inversely proportional to the distance between
them for a parallel-plate capacitor.
The input impedance of microphone is very high at audio frequencies and its
output is low thus it needs to interface high input impedance. Microphone is usually a
FET based buffer which is built in the microphone capsule. It acts as an impedance
transformer typical the output impedance is in order of few ohms. The sensitivity of the
microphone is typically 17mV/Pa and the frequency response is flat from less than 100
Hz to 10 kHz within 3dB which is an ideal detector for photoacoustic detection system.
The acoustic detector is shown in Fig.2.5. The specifications of the microphone are
shown in Table 2.4
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Table 2.4 Specifications of Acoustic (Microphone) detector
S. No Parameter Value
1 Supply voltage range 0.9 to 1.6VDC
2 Current drain @ 1.3VDC 24mA typical, 50mA maximum
3 Frequency response/sensitivity 100 to 10 kHz
4 Sensitivity 10dB/Pascal
5 Sensitivity tolerance ± 3dB @ 1kHz
6 Dynamic output impedance 4.4 ohms typical
7 DC Output voltage Range 0.2 to 0.7VDC
8 Input-referred self-noise level 27dB typical, 30dB maximum
9 Output self-noise -100dBV maximum
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Section 2.7
LOW NOISE PREAMPLIFIER
Normally acoustic detector produces very low voltage in the range of nano-volts to
micro volts. To measure such voltage from the acoustic detector, an ordinary
amplifier cannot be used. Hence, a low noise instrumentation amplifier INA 163 is
used which offers very low noise, low distortion, wide bandwidth, high input
impedance and dynamic response over a wide range of gain. It is ideal for low-level
audio signals of balanced low-impedance acoustic detectors or microphones.
The instrumentation amplifier INA 16310
amplifies the acoustic signal from micro
volts to few volts without noise. INA 163 maintains very low input bias current and
precise input characteristics over its full input common-mode voltage range. It offers
a very low drift of ±10µV/oC and high open loop gain of 100dB. The INA 163 is
unique in distortion cancellation circuitry and also reduces distortion in extremely
low level signals even at high gain. The INA 163 provides near to theoretical noise
performance at source impedance 200Ω and a simple external resistor sets the gain
up to 2000. The differential inputs of instrumentation amplifier provide superior
performance in professional microphone applications. The INA163 operates wide
supply voltage +4.5 to +18V, an excellent output voltage swing and drives high
output current. The outstanding performance characteristics of INA 163 allow its use
in the most critical instrumentation applications.
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GAIN-SET RESISTOR
A simple single resistor is used to set the required gain of instrumentation amplifier
INA 163. The INA 163 has two internal 3k ohm feedback resistors with laser-
trimmed. The gain of amplifier is calculated as follows
Gain, G =1+6000/ RG
where RG is a gain resistor. An external gain resistor is used to adjust the gain up to
2000. The low noise instrumentation amplifier circuit is shown in the Fig. 2.6.
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Section 2.8
LOCK-IN AMPLIFIER
For several applications lock-in amplifier requires the measurement of very low level
signal of about nano-volt (nV) amplitude obscured by noise. To achieve this task a lock-
in amplifier is normally used. The lock-in amplifier for embedded based photoacoustic
system is designed and implemented in the present study. It is a type of amplifier and a
narrow bandpass filter which can extract the signal from extremely noise environment.
Lock-in amplifier eliminates the noise even bandwidth is less than 0.1Hz and provide
the quality factor more than 103. It can amplify up to 180 dB. Lock-in amplifier11 is
used to measure the amplitude and phase of acoustic signal.
The lock-in amplifier consists of input amplifier, bandpass filter, phase locked
loop (PLL), phase sensing detector (PSD), low pass filter and output amplifier. The
block diagram of the lock-in amplifier is shown in Fig.2.7. The input amplifier amplifies
the acoustic signal from micro volts to milli volts and applies to the phase sensing
detector through a bandpass filter. The PLL uses the square wave of function generator
as the reference signal and it applies to the phase sensing detector through the phase
shifter. The phase shifter is employed to define a zero phase. The output of phase locked
loop consists of precise square wave and in-phase to the reference frequency. The PSD
output produces the result of phase difference and amplitude of the acoustic signal. The
sub-modules of lock-in amplifier are described.
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Low offset operational amplifier
Operational amplifier OPA 177 is a low noise and high input impedance amplifier. It
offers very low offset voltage 25µV, low drift voltage 0.3µV/deg C and good accuracy.
The high performance makes ideally suited to precision instrumentation. The low
quiescent current of the OPA177 dramatically reduces warm-up drift and errors due to
thermoelectric effects in input interconnections.
The low offset operation amplifier12 OPA177 is used to amply the output signal
of phase sensing detector. The OPA177 is employed in the configuration of non-
inverting amplifier. The output voltage of OPA177 is calculated by the following
equation.
Vout = 1+R2/R1 x Vin
Where R2 is feedback resistance, R1 is input resistance and Vin is input voltage of
OPA117.
Bandpass filter
The bandpass filter of lock-in amplifier is employed to pass the frequencies within
certain range and rejects the frequencies outside of the range. The two types of bandpass
filters are generally used such as Active bandpass filter and passive bandpass filter. The
active bandpass filter requires an external power supply to make the use of active
components such as transistors or integrated circuits. The external source is not required
to make use of passive components such as capacitors, resistors and inductors etc. The
active bandpass filter is used to implement the lock-in amplifier in the present study.
The bandpass filter circuit is shown in Fig. 2.8.
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The integrated circuit MAX 749013 is a universal switched capacitor filter,
which is used to design a band pass filter in the present study. It offers low power, low
operating voltage, Rail-to-Rail and wide dynamic range. The two clocking options are
available in the MAX9490, one is self-clocking and another is external clocking for
tighter cutoff frequency control. The ratio of clock to center frequency is 100:1. The
maximum center frequency of bandpass filter is 40kHz. MAX9490 operates a single
power supply which is available in SOP package of 16 pins. The center frequency of the
bandpass filter is calculated as follows.
Fo = fclk/100
= 205300/100
= 2053 Hz
Phase-Locked Loop
The modulating signal of the laser source is to be controlled. Hence the need to use the
phase -locked loop (PLL). In the present study, the phase-locked loop (PLL) HC7046 of
Texas instruments is used. The PLL HC7046 is a closed-loop frequency control system
based on the phase difference between the input clock signal and the feedback clock
signal of a controlled oscillator. The HC704614 offers excellent frequency linearity, high
speed,
wide range of operating voltage. The HC7046 consist of a voltage controlled oscillator
(VCO), comparator and low pass filter. The phase-locked loop circuit diagram is shown
in Fig. 2.9.
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The phase comparator of PLL HC 7046 compares two input signal phases and
produces an error signal which is proportional to their phase difference. The error signal
controls the phase of voltage controlled oscillator15
. The VCO produces a negative
feedback if the output phase is drift, the error signal will increase and drive the VCO
phase in the opposite direction so as to reduce the error. Thus the output phase of VCO
is locked to other input phase. The capture frequency of VCO is calculated as follows
VCO frequency, Fosc = M (VCO/R) / 2C Vramp
= 6.2 (2.5/34.2k) / 2x600pf x 1.8
= 209.82k Hz
where M is multiplication factor and Vramp is ramp voltage.
Phase Sensitive Detector
Phase sensitive detector (PSD) is the heart of the lock-in amplifier. To measure the
phase difference of acoustic signal and reference signal, the need to use the phase
sensing detector16 A precision phase sensing detector AD630 in demodulator
configuration is used in present study. The AD630 consists of comparators, amplifiers
and laser trimmed capacitors. It offers wide bandwidth, low offset voltage and high
precision. The AD630 operates within a range of voltage from 5 to 16 volts. High slew
rate and fast settling time allow accurate signal processing in pulse conversion
applications.
The reference signal of laser source and acoustic signal through PLL and
bandpass filter17
are given to phase sensing detector AD 630. The phase sensing detector
processes these signals and produces DC voltage through a low-pass filter which is
proportional to the amplitude of acoustic signal18
and phase difference of inputs signals.
If these input signals are 90o out of phase, the output voltage of AD630 will be zero.
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The low frequency noises of AD630 are removed by low-pass filter. The AD630 circuit
is designed and developed in present study which is shown in Fig. 2.10.
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Section 2.9
TEMPERATURE SENSING UNIT
In order to measure the temperature in photoacoustic gas cell, the temperature is to be
sensed and measured. This unit consists of a temperature sensor LM3519
and the
associated circuitry which is shown in Fig. 2.11. The LM35 is a precision integrated-
circuit temperature sensor whose output voltage is linearly proportional to the
centigrade temperature. The LM35 does not require any external calibration or trimming
to provide typical accuracies of ±.0.5 °C at room temperature and ±1°C over a
temperature range from −40 to +120°C. The circuit has a dynamic impedance of less
than 1 ohm and operates within a range of current from 100 µA to 5mA. The LM35 has
a very low self-heating 0.08°C in the air. It operates linearly over a temperature range of
−40 to +120°C. The output of the LM 35 is calculated as follows.
Vo= 10mV / OC
The temperature measurement unit is designed and constructed. The circuit is
tested for different temperature measurements The results are presented in Table 2.5.
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Table 2.5 : Temperature measurements
S. No. Temperature in
Thermometer ( oC)
Temperature in the
present system (oC)
Temperature in milli
volts
1 4.0 4.0 40.20
2 6.0 6.0 60.10
3 8.0 8.0 80.00
4 10.5 10.5 105.00
5 12.2 12.2 122.01
6 14.5 14.5 145.20
7 16.0 16.0 160.00
8 18.0 18.0 180.00
9 20.5 20.5 205.01
10 25.2 25.2 252.10
11 30.0 30.0 300.10
12 35.0 35.0 353.10
13 40.0 40.0 400.10
14 50.0 50.0 500.10
15 60.0 60.5 605.10
16 70.0 70.0 700.15
17 80.0 80.0 800.30
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Section 2.10
PRESSURE SENSING UNIT
In order to maintain the sufficient pressure in photoacoustic gas cell, the pressure is to
be sensed and measured. This unit consists of a pressure sensor MPXV505020
and the
associated circuitry which is shown in Fig. 2.12. The MPXV5050 is a precision
integrated silicon pressure sensor which consists of on-chip temperature compensation
and calibration. In the present study, the MPX5050 pressure sensor is used to measure
the pressure of gas sample in photoacoustic cell.
The single element of pressure sensor combines advanced micro machining,
thin-film materialization and bipolar processing to provide an accurate and high-level
analog signal. The output voltage of pressure sensor is directly proportional to the
applied pressure. The MPXV5050 operates within a range of voltage from 4.75 to
5.25V. Unlike other sensors, the MPX5050 have a linear output. It operates linearly over
a pressure range of 0Kpa to 50Kpa.
The pressure measuring unit is designed and constructed. The circuit is tested for
different pressure measurements. The results are tabulated in Table 2.7
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Table 2.6 : Specifications of pressure sensor MPX5050
S. No Parameter Value Unit
1 Pressure range 0 to 50 kPa
2 Supply current 7 mA
3 Pressure offset voltage 0.2 Volt
4 Full scale span @ 0-85 deg C 4.5 Volt
5 Accuracy @ 0-85 deg C 2.5 %V
6 Response time 1 mS
7 Offset stability +0.5 Vfss
Table 2.7 : Performance of pressure sensor
S. No Input pressure
(kPa)
Corresponding output
(Volts)
1 0 0.20
2 5 0.45
3 10 0.90
4 15 1.35
5 20 1.80
6 25 2.25
7 30 2.70
8 35 3.15
9 40 3.60
10 45 4.05
11 50 4.50
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Section 2.11
ANALOG TO DIGITAL CONVERTER
The analog voltage corresponding to the air pollutant is converted into digital signal that
the microcontroller can understand. The analog to digital converter (ADC) is a device
that transforms data in the form of continuous analog variable into a discrete binary
code suitable for digital processing and is the core of any data acquisition system. In the
present study, 16-bit analog to digital converter AD7655 is used.
The Analog devices corporation AD7655 is a precision analog to digital
converter and combines successive approximation conversion. It operates a single 5V
power supply. It offers 16-bit resolution, dual channel, low noise, wide bandwidth,
simultaneous sampling, high-speed, internal conversion clock, error correction and both
serial and parallel ports. The track-and-hold of ADC has a 4-channel multiplexer and
one control input (A0). The control input A0 allows the simultaneously sampling of
input pairs INA1/INB1 (A0=low) or INA2/INB2 (A0=high). AD7655 operates within a
range of temperature from -25°C to 85°C. The features of analog to digital converter
AD7655 are as the follows
• Built-in track-and-hold amplifiers.
• 1 MSPS of Sampling Speed.
• Wide range of analog input voltage from 0 V to 5 V.
• No pipeline delay.
• SPI / QSPI / MICROWIRE / DSP compatible
• Power dissipation less than 5 mW
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The component values are selected for optimum performance of the ADC for full-scale
voltage as recommended by the manufacturer’s data sheet which will result in a
resolution of 0.07mV/LSB.
Interfacing of ADC 7655 analog to digital converter wit
microcontroller
The Interfacing circuit of analog to digital converter AD7655 is shown in Fig. 2.13. The
output of the ADC AD7655 is in digital data form on pin D0 to D15, which is the
corresponding voltage of analog input. The digital data is placed on port pins of ARM
microcontroller. The D0 is the most significant bit and D15 is the least significant bit of
the ADC. The control pins of ADC converter are serial or parallel (SEP/PAR), end of
conversion (EOC), busy bit (BUSY), chip selection (CS), read (RD), channel selection
(A/B) and byte swapping (BYTESWAP) used to control the ADC while the conversion
of analog to digital data. In this present study, the ADC AD7655 is used in parallel
mode to get the digital output simultaneously and interfaced with the ARM
Microcontroller. The clock for ADC of frequency 24 MHz is derived from the external
crystal.
The detailed program, developed in C language on these lines, finds as a
subroutine in the main program which is presented in software development sections.
The performance of the analog to digital converter is tested and the results are shown in
Table 2.8.
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Table 2.8 : Performance of data acquisition system
S.No. Input Voltage
(Volt)
Corresponding ADC Output
(Volt)
1 0.00 0.000
2 0.25 0.250
3 0.50 0.500
4 0.75 0.750
5 1.00 0.999
6 1.50 1.500
7 2.00 2.099
8 2.50 2.498
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Section 2.12
ARM MICROCONTROLLER UNIT
The role of ARM microcontroller unit in the present study is to perform the following
tasks
• To measure the voltage of acoustic detector.
• To measure inside temperature of the photoacoustic cell.
• To measure inside pressure of photoacoustic cell.
• To process the measurement data.
• To display the measured data on LCD display.
The general purpose I/O lines P0.16 - P0.31 of microcontroller are used to data
lines D0-D16 of ADC for measurement of air pollutants, temperature and pressure. The
control lines of ADC such as Data channel selection (A0), Multiplexer selection (A/B),
Serial/Parallel selection (SER/PAR), Parallel mode selection (BYTESWAP), Busy bit
(BUSY), End Of Conversion (EOC), Read Data (RD) and Chip Select (CS) are used to
control the conversion of analog to digital converter by microcontroller. To display the
measurement data, the LCD display is interfaced with microcontroller. The data lines
D0-D7 and control lines P.28-P.30 (RS, R/W and EN) of LCD display and port lines of
P0.20-P.27 of microcontroller are used for measurement data of air pollutants,
temperature and pressure, the microcontroller. The LCD display is interfaced with
microcontroller through a latch 74HC573. For these tasks we used LPC2106
microcontroller which is shown in Fig.2.14.
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The ARM Microcontroller is a 32-bit RISC22
processor architecture which is
developed by ARM Limited that widely used in embedded systems nowadays. The
power saving features of ARM CPU is dominant in where the critical design goals of
low power consumption. Today, the ARM family accounts for approximately 90% of all
embedded 32-bit RISC CPUs. The LPC210623
is a 32-bit Microcontroller,
ARM7TDMI-S CPU with real-time emulation. The 128-bit wide memory interface and
a unique accelerator architecture enable 32-bit code execution at maximum clock rate.
For critical code size applications, the alternative 16-bit Thumb mode reduces code by
more than 30 % with minimal performance penalty. Due to their tiny size and low
power consumption, this microcontroller is ideal for embedded applications where
miniaturization is a key requirement such as measurements, access control and point-of-
sale. The PWM channels and 32 GPIO lines make this microcontroller particularly
suitable for industrial control, analytical and medical systems. The salient features of
LPC microcontroller are as follows
32-bit ARM7TDMI-S processor.
64 KB on-chip Static RAM.
128 KB on-chip Flash Program Memory.
128 bit wide interface/accelerator.
Enables high speed 60 MHz operation.
In-System Programming (ISP) and In-Application Programming (IAP) via on-
chip boot-loader software.
Vectored Interrupt Controller with configurable priorities and vector addresses.
Multiple serial interfaces including two UARTs, Fast I2C and SPI.
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Two 32-bit timers, PWM unit (6 outputs), Real Time Clock and Watchdog timer.
32 general purpose I/O pins in a tiny LQFP48 package.
On-chip crystal oscillator with an operating range of 1 MHz to 30 MHz.
Processor wake-up from Power-down mode via external interrupt.
Individual enable/disable of peripheral functions for power optimization.
Dual power supply: CPU operating voltage range of 1.65 V to 1.95 V.
I/O power supplies range of 3.0 V to 3.6 V with 5 V tolerant I/O pads.
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Section 2.13
LIQUID CRYSTAL DISPLAY
In the present study, the LCD display FDCC200424 is used for displaying the measured
air pollutant, temperature and pressure of the emission gas. The display is a 5x8 dot
matrix liquid crystal display that display alphanumeric, character and special symbols. It
is a 20 characters and 4 line LCD display unit. The LCD consists of in-built controller
and driver that provide connectivity between a dot matrix LCD and microcontroller. The
LCD FDCC2004 is manufactured by Fordata Electronic Corporation Pvt. Limited,
China. The features of the LCD display FDCC2004 are as follows
5x8 dots with cursor.
Easy interface with 8 –bit mode.
Built-in controller in LCD module.
Display data RAM contains 80 characters.
5 Volts power supply.
Low power Consumption.
High contrast and wide viewing angle.
The liquid crystal display is interfaced with the ARM Microcontroller LPC2106
in the present study. Microcontroller reads the data from each channel of analog to
digital converter and displays the data on LCD display. The concentration of air
pollutant is displayed on first line; the sample pressure in photoacoustic cell is displayed
on second line and the sample temperature is displayed on third line of LCD display.
The pin and interfacing detail of LCD with the microcontroller are given in Table 2.7
and Table 2.8.
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Table 2.7 : Pin assignment of LCD display
Pin Symbol Function
1 Vss GND
2 Vdd Power supply
3 V0 Contrast Adjust
4 RS Register Select
5 R/W Data Read/Write
6 E Enable signal
7 – 14 D0 – D7 Data lines
15 LED + Power supply (+)
16 LED - Power supply (-)
Table 2.8 : Interfacing of Microcontroller with LCD display
Microcontroller
I/O pins
LCD display
P0.20 – P0.27 Data byte (D0 – D7)
P0. 28 Register selection (RS)
P0.29 Read/Write(R/W)
P0.30 Enable (E)
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The 74HC57325 is a high-speed octal transparent latch. It is used as a line driver
between the microcontroller and LCD display. The input lines D0-D7, output enable OE
and output lines Q0 – Q7 of 74HC573 are used for LCD display. The interfacing of
LCD display with ARM microcontroller LPC 2106 is shown in Fig. 2.15. The pin
details of 74HC573 are given in Table 2.9.
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Table 2.9 : Pin assignment of latch 74HC573
Pin Symbol Function
1 OE Output enable
2-9 D0 – D7 Data inputs
10 GND Ground
11 LE Latch enable
12 – 19 Q7 – Q0 Data outputs
20 VCC Supply
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Section 2.14
POWER SUPPLY UNIT
The embedded based photoacoustic system requires the following D.C supply voltages
to operate the system.
± 5V/500 mA
± 12V/500 mA
The transformers with secondary ratings 15–0–15V/1A are selected to meet the required
specifications.
The circuit diagram of the power supply unit is shown in Fig.2.16. Three pin IC
regulators 7805 and 7905 are used to get the 5V and -5V power supply and 7812, 7912
for +12V and –12V power supplies. The diodes 1N4007 used for rectification and the
filter capacitors C1and C2 are 330µF/25V used to eliminate the fluctuations. The C3,
C4, C5 and C6 of 0.lµF are used to eliminate the high frequency components. The
power supplies designed in the present study gives required voltages within ± 0.01%
line and load regulation. The individual blocks of the present study are tested with the
power supply.
The hardware circuits of the present system are tested with the various gas
samples. The detailed schematic diagram of the embedded based measuring system is
shown in schematic diagram.
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Section 2.15
SCHEMATIC DIAGRAM AND WORKING
The schematic diagram of design and development of embedded based photoacoustic
system is designed and implemented. The modulated laser source is used to generate the
acoustic signal in photoacoustic resonant cell. The Photoacoustic (PA) resonant cell is
specially designed and fabricated for gas analysis, which is used to generate an acoustic
signal in order of milli volts (amplitude) at 2055 Hz of frequency. Generated acoustic
signal is detected by professional microphone, which is connected to the PA cell. The
low noise pre-amplifier INA163 is used to amplify the signal of acoustic detector. The
output signal of pre-amplifier is used to bandpass (MAX7490) filter, which eliminates
the noise of low and high pass frequencies and allow specific bandwidth of frequency.
The output signal of bandpass filter is used as input to phase sensitive detector (PSD).
The function generator (XR2206) is constructed to generate the square wave
about 2055 Hz of frequency, which is used to laser source. The laser is electronically
modulated at given frequency, it is also used as a reference signal to the phase-locked
loop and the phase sensitive detector. The PA signal and reference signals are used to
the phase sensing detector (PSD). The PSD picks up only the signal from the noises,
which is the same frequency of the reference signal. The output signal of the PSD is
used to the channel 1 of Analog to digital converter through the gain operational
amplifier.
The output signal of temperature sensor LM35 is used to the channel 2 of
Analog to digital converter through operational amplifier OPA117. The output signal of
pressure
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sensor MPX5050 is applied to the channel 3 of analog to digital converter through
operational amplifier OPA117. The analog to digital converter AD7655 contains 4
analog input channels, which are used to PA signal, temperature sensor and pressure
sensor. The output digital data of ADC is connected to the microcontroller LPC2106.
The microcontroller sends the data to the 4-line LCD display. The final data is displayed
line by line on 4-line LCD display. The schematic diagram and PCBs of the embedded
based photoacoustic system are shown in Figs. 2.17, 2.17(a), 2.17(b), 2.17(c), 2.17(d)
and 2.18.
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Section 2.16
SAMPLE HANDLING UNIT
The sample handling unit is used to collect the gas samples from various industrial
emissions. It consists of a suction pump, connecting tubes, dust particle filter, buffer
tank and flow regulator. The inlet tube of suction pump21
is connected to stainless steel
pipe and outlet is connected to the input of buffer tank. The stainless steel pipe can
withstand at high temperatures. The buffer tank stores the gas sample and supplies to the
photoacoustic cell without flow fluctuations through a dust filter and air flow
regulator22
. The dust filter is used to collect the dust particles and allow very fine
particles to the photoacoustic cell through a flow regulator. The flow regulator
maintains a required flow rate about 1.5 Lt/min of gas sample. The photoacoustic cell
maintains the pressure up to 20 KPa of gas sample at room temperature.
After completion of the gas sampling process, the complete photoacoustic
system will be ready to measure the air pollutants in the industrial and automobile
emissions which is shown in Fig.2.19.
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REFERENCES
1. C Haisch and R Niassner, Spectroscopy Europe, 14, 11 (2002).
2. Andra Miklo and Peter Hess, Review of Scientific Instruments, 72 (2001).
3. V Deepak Bageshwar, S Avinash Pawar and V Khanvilkar, Eurasian J. Anal.
Chem.,5, 187, (2010).
4. The datasheet of Function Generator XR2206 (www.bucek.name/pdf/xr2206.pdf).
5. J M Frans Harren, Gina Cotti, Jos Omens and Sacco Hekkert, “Photoacoustic
Spectroscopy in Trace Gas Monitoring”, John Wiley & Sons Ltd. (2006).
6. F J M Harres, F G C Bijnen, 30, 137, Netherlands (1990).
7. Frank Muller, Alexander Popp and Frank Kuhnemann, Optical Society of America,
11, 2820,Germany (2003).
8. A Tavakoli, M Taheri and H Saghafifar, “Design, Simulation and Structural
Optimization of a Longitudinal Acoustic Resonator for Trace Gas Detection using
Laser Photoacoustic Spectroscopy”, ICOP 2009-International Conference on Optics
and Photonics, India (2009).
9. Zoltan Bozoki, Janos Sneider, Zoltan Gingl and Gabor Szab, Measurement Science
Technology, 10, 999 (1999).
10. The Data sheet of Preamplifier INA163,
http://www.ti.com/lit/ds/symlink/ina163.pdf.
11. H Scofield John, American Journal of Physics, 62, 129 (1994).
12. The Datasheet of Low Noise Preamplifier
(http://www.ti.com/lit/ds/symlink/opa177.pdf).
13. Kerry Lacanette, “Basic Introduction to Filters—Active, Passive and Switched-
Capacitor”, National Semiconductor, Application note 779, (2010).
14. Garth Nash, “Phase-Locked Loop Design Fundamentals”, Freescale Semiconductor
Application note, Document number: AN535, Rev. 1.0, (2006).
15. The Datasheet of Phase Locked Loop (http://www.alldatasheet.com/datasheet-
pdf/pdf/ 15655/PHILIPS/74HC7046A.html).
16. G Bradley Armen, “Phase Sensitive Detection: The lock-in Amplifier”, Department
of Physics and Astronomy, The University of Tennessee, Knoxville, Tennessee
(2008).
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17. Jim Karki, “Active Band-pass Filter Design”, Application Report, Texas
Instruments (2000).
18. Jimmy Ng and A H Kung, Optics Letters, 29, 1206, Taiwan (2004).
19. The Datasheet of Temperature Sensor (http://www.ti.com/lit/ds/symlink/lm35.pdf).
20. The datasheet of Calibrated Pressure Sensor, web link :
http://www.datasheetcatalog.org/ datasheet2/e/0z5dil0g15741p7huyq7xj1e8a3y.pdf.
21. Suction Pump, Model No. HS-WP-1, High Speed Appliances, Manufacture,
Mumbai,
India.
22. Flow Regulator, TRAC Model No. 35BO, Transducers and Controls Pvt. Limited,
Hyderabad, India.
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CHAPTER 3
Design and Development of Embedded
Based Photoacoustic Measurement
System - Software Development
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Section 3.1
SALIENT FEATURES OF EMBEDDED C LANGUAGE
The C language is a general-purpose computer programming language developed in
1972 by Dennis Ritchie at the Bell Laboratories. The C programming language is the
most popular programming language for programming desktop computers. The
embedded C language1 is a subset of C language. It is a popular programming
(1,2)
language for microcontroller based systems. The embedded C is growing in importance
for embedded systems and real-time operating system applications. Exactly as the PC is
the standard for personal computing, the ARM microcontroller is the standard for 32-bit
microcontroller. The concept of embedded C compiler3 for ARM microcontroller
executing on a PC is familiar now. Embedded C language is an inherent language,
flexibility and portability across a wide range of hardware. The specific reasons are
mentioned below for use of embedded C
Embedded C language is a programming language for microcontrollers.
It is developed for embedded system programming and also used for real
time application programming4.
Embedded C language is a mid-level with high-level features such as
support for functions and modules in embedded systems.
It is code flexibility, efficiency and ability to access specific hardware
via pointers.
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Using embedded C library functions and header files ensure that application
source code can be recompiled for different microcontroller targets.
Well-established embedded C compilers are available for embedded systems
such as KEIL5 and RIDE compilers for 8-bit to 32-bit microcontrollers.
Embedded C language breadth of expression is brief and powerful.
Debugging and maintaining code written in embedded C is much easier than
code written in assembly language.
Characteristics of embedded C language
Embedded C is a language of functions, data types6, assignments and flow controls. To
program in embedded C, one must call a function and most functions return values. The
value returned from a function, the value of data variable or the value of constant could
be used in an assignment statement to change the value of another variable. With the
addition of flow is control if, while, for and do-while in embedded C.
Embedded C language contains a small set of data types: Signed and unsigned
integers, characters, floating point numbers7, characters, bit fields and enumerated
types. In embedded C, one can declare a pointer variable that points to any data type.
The address arithmetic of embedded C is sensitive to the properties of the pointer being
adjusted. Pointers to functions are also supported in embedded C. The data types can be
extended by building structures that are hierarchies of members, each member being
one of the data types or an earlier-declared structure. Arrays of data types can be
declared. An array consists of any data type, including a structure or union. Arrays can
have multiple dimensions.
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Some of the important decision making statements, control instructions,
functions, arrays and pointers of embedded C language8 used in developing the present
project software are described as fellows
(a) if statement
if statement is available in embedded C. It is a powerful decision making statement and
used to control the flow of execution of statements. The general of if statement is as
follows
if (expression)
Statement -1
Statement -2
Statement -3
It is two-way statement. An expression is valid which executes the following statement-
1 and statement-2 otherwise expression is false control comes out from the loop and
executes the outside statement-3.
(b) while loop
The while loop evaluates the test expression before every loop, it can execute non-zero
times if the condition is initially true. The general form of while loop is shown as
follows
while (expression)
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Statement
Example :
int x =1;
while (x<20)
Printf (“%d\t”, x);
x = x+1;
(c) for loop
The for loop in embedded C is the most general looping construct. The loop header
contains three parts such as initialization, continuation condition and action. The
general form of for loop is as shown below
for (initialization; continuation; action)
Statement
The initialization is executed once before the body of the loop is entered. The loop
continues to run as long as the continuation condition remains true. After every
execution of the loop, the action is executed.
The following example executes 10 times by counting 0 to 9. Many loops look very
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much like the following
Example :
int i;
for (i = 0; i < 10; i ++)
printf (“%d \n”, i);
(d) Function
A function6 in embedded C language is a block of code or statements that performs a
specific task. It has a name and it is reusable i.e. it can be executed from as many
different parts in a embedded C program as required. It also optionally returns a value
to the calling program. Function has obtained some of special properties which are as
follows.
(i) Every function has a unique name. This name is used to call function from “main
()” function. A function can be called from within another function.
(ii) A function is independent and it can perform its task without intervention from or
interfering with other parts of the program.
(iii) A function performs a specific task. A task is a distinct job that your program must
perform as a part of its overall operation.
(iv) A function returns a value to the calling program.
Example :
address ();
printf(“\n SK University, Anantapur, India”);
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address ()
printf (“ \n Dept. of Instrumentation");
(e) Array
An array in embedded C language is a collection of similar data-type. It can hold value
of a particular data type, which has been declared. Arrays can be created from any of
the embedded C data-types such as int, float and char. An integer array can only hold
integer values and cannot hold values other than integer. When we declare an array, it
allocates contiguous memory location for storing values whereas 2 or 3 variables of
same data-type can have random locations. It is the most important difference between a
variable and an array.
Syntax : data_type array_name[width];
Example:
int array[6];
int sum = 0; sum = array[0] + array[1];
printf (“\n%d”, sum);
(f) Pointer
A pointer6666 is a secondary data type also known as derived data type in
embedded CCCC. It is built from one of the primary data types available in
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embedded C C C C language. Basically pointer contains memory address of other
variable or function as their value. As pointer deals with memory address, it can
be used to access and manipulate data stored in memory.
Benefits of pointer in embedded C program
Pointer is one of the most exciting features of embedded C language and it has added
power and flexibility to the language. Pointer offers following benefits to the
programmers
Pointers can handle arrays and data tables efficiently.
Pointers can support dynamic memory management.
Pointer helps to return multiple values from a function through function
argument.
Pointer increases program execution speed.
Pointer is an efficient tool for manipulating structures, linked lists, queues
stacks etc.
Syntax : data_type* pointer name;
Example:
int i=9,*ptr;
ptr=&i;
printf("Value of i : %d\n",i);
printf("Address of i : %u\n",&i);
printf("Address of ptr : %u\n",&ptr);
printf("Ptr pointing value :%d",*ptr);
getch();
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The outputs are
9
65524
65520
9
KEIL embedded C CROSS COMPILER
Keil is a embedded C cross compiler which is used to translate high-level program to a
low-level language. It is a 32-bit integrated development environment9 which supports a
set of development tools for ARM 32-bit microcontroller10
applications. Keil was
founded in 1986. Keil developers have built up many years of experience to develop
embedded C cross-compilers. The development tools of Keil are a complete solution to
developing software for ARM 32-bit and 8051 8-bit families of microcontrollers. It can
be used to create a source file, compile, link and covert options with an easy to use user
interface. Keil cross compiler contains a real view compilation tool, micro vision IDE
and debugger(3,9)
.
In present work, embedded C language is chosen to develop the software for
embedded based photoacoustic system for measurement of air pollutants.
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Section 3.2
SOFTWARE DEVELOPMENT
The software is developed in embedded C language using KEIL cross compiler for
measurement of air pollutants in automobile and industrial exhausts. The main role of
the software in the present study is to govern the following activities using ARM 32-bit
microcontroller.
17. To acquire the data from various detectors through the ADC such as acoustic
detector, temperature detector and pressure sensor.
18. To make the data acquisition system and convert the analog to digital data.
19. To compute and display of air pollutants, photoacoustic cell temperature and
pressure measurements.
20. To make the different functional units of system work in a systematic and
sequential manner.
21. The necessary software in the present study is developed in embedded C
language to implement these tasks for effective functioning of the system.
Software Routines
The software program developed in the present study is divided into five parts using the
functions in embedded C language. Each routine is described as follows.
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1. Display the name of measurement on LCD routine
Initialization of microcontroller (General I/O Port, Pin direction, clock).
Send the command for register selection (RS).
Send the command for Read / Write (R/W).
Write the name of display on I/O port.
High the enable pin of LCD then Low.
Call delay.
2. Detection of air pollutant routine
Initialization of microcontroller (General I/O Port, Pin direction, clock).
Select the channel-1 of ADC.
Write the command for start of conversion of ADC.
Read the busy bit until it is low.
Equate the digital data to analog data.
Display the analog data on LCD display.
Call delay.
3. Measurement of Temperature routine
2 Initialization of microcontroller (General I/O Port, Pin direction, clock).
3 Select the channel-2 of ADC.
4 Write the command for start of conversion of ADC.
5 Read the busy bit until it is low.
6 Equate the digital data to analog data.
7 Display the analog data on LCD display.
8 Call delay.
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4. Measurement of Pressure routine
Initialization of microcontroller (General I/O Port, Pin direction, clock).
Select the channel-3 of ADC.
Write the command for start of conversion of ADC.
Read the busy bit until it is low.
Equate the digital data to analog data.
Display the analog data on LCD display.
Call delay.
5. Simultaneous display of all parameters on LCD display routine
10. Initialization of microcontroller (General I/O Port, Pin direction, clock).
11. Display the name of instrument on first line.
12. Display the concentration of Air pollutant in ppm on second line.
13. Display the temperature in degree centigrade on third line.
14. Display the pressure in Kilo Pascal (KPa) on fourth line.
15. Display the analog data on LCD display.
16. Call delay.
The software program (hex code) is dumped into flash memory of LPC2106 by
using the Philips flash programmer11
through RS232 communication protocol12
. The
program is ready to execute in LPC2106 microcontroller for real time applications. The
detailed flow charts of software program of the present system is developed as follows
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Fig. 3.1 : Flow chart diagram of embedded based photoacoustic system for
measurement of air pollutant
Clean & Purse the PA
gas cell
Inject the sample to the PA cell
Switch ON the measurement
system
Run the software to measure
the air pollutant
Start
Select channel 1
Read ADC output corresponding to the
air pollutant concentration
Compute and display on LCD
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Fig. 3.2: Flow Chart diagram for Temperature and Pressure measurement
Select channel-2
from ADC
Read ADC output corresponding
to the existing temperature
Compute the temperature
value
Display in degree
centigrade on LCD
Start
Select channel- 3
from ADC
Read ADC output corresponding
to the existing pressure
Compute and the display of the
pressure value on LCD
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Section 3.3
PROGRAM IN DETAIL
The software is developed for the measurement of air pollutants such as nitrogen
dioxide, carbon soot and aerosols. The temperature and pressure of the gas sample in
PA cell are also measured simultaneously. In present study, the program is developed in
embedded C language using KEIL C cross compiler. The program in detail is given
below.
Program Details
***** Program for the measurement of air pollutants *****
-------------------------------------Header files -------------------------------------------------
#include<stdio.h>
#include<LPC210X.H>
#include<stdlib.h>
------------------------------------- Definitions --------------------------------------------------
#defineLCD_INIT 0X38 //LCD initialization
#defineDispOn_CursorBlink 0x0C
#defineClrDisplay 0x01
#defineCursrRightShift 0x06
#define rs 0x10000000 // Register selection
#define rw 0x20000000 // Read/Write
#define en 0x40000000 //Enable
#define Latch 0x80000000
#define Clear 0xFFF00000 // Clear controller port pins
#define busy 0x08000000 // Busy bit of ADC
#define RESOL 0.000076 //76 µV resolution-16bit adc
------------------------------------- Functions --------------------------------------------------
void clk_int(void);
void lcd_int(void);
void lcd_string(char *senpoint);
//void lcd_string1(char *senpoint1);
//void lcd_string1();
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void lcd_line1(void);
void lcd_line2(void);
void lcd_line3(void);
//void lcd_line4(void);
void DataSend();
void DataSend1();
void DataSend2();
void lcd_display();
void lcd_display1();
void lcd_display2();
void lcd_display3();
void lcd_display4();
void lcd_line1_m(void);
void lcd_line2_m(void);
void lcd_line3_m(void);
void lcd_line4_m(void);
void delay_ms();
void delay_us();
void lcd_cmd(unsigned int letter);
void lcd_char(unsigned int letter);
//void lcd_char1();
void lcd_busy(void);
void cmdwrt(void);
void datawrt(void);
-----------------------------------Initialization -----------------------------------------------------
unsigned char OUTPUT1[5];
float Gfltfs_temp;
unsigned int Ddata;
int DIGITAL_DATA1,DIGITAL_DATA2;
----------------------------------Delay function ----------------------------------------------------
void delay_ms(int x)
int a,b;
for(a=0;a<x;a++)
for(b=0;b<3500;b++);
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---------------------------------LCD command writes function ----------------------------------
void cmdwrt()
IOSET = Latch;
IOCLR =rs;
delay_ms(5);
IOCLR =rw;
delay_ms(5);
IOSET =en;
delay_ms(20);
IOCLR =en;
delay_ms(5);
-------------------------------- LCD command initialization function ---------------------------
void lcd_cmd (unsigned int letter)
IOCLR = 0x0FF00000;
IOSET = Latch;
Ddata =(letter<<20 );
Ddata=Ddata & 0xFFF00000;
//lcd_busy();
IOCLR = en;
IOSET =Ddata;
IOCLR = ~ Ddata;
delay_ms(5);
cmdwrt();
----------------------------------LCD data write function -----------------------------------------
void datawrt()
IOSET = Latch;
IOSET =rs;
// delay_ms(5);
IOCLR =rw;
// delay_ms(5);
IOSET =en;
delay_ms(10);
IOCLR =en;
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// delay_ms(5);
------------------------------ LCD Character display ------------------------------------------
void lcd_char(unsigned int letter)
//delay_ms(5);
IOSET = Latch;
IOCLR = 0x0FF00000;
Ddata =(letter<<20);
Ddata=Ddata & 0xFFF00000;
IOSET =Ddata;
IOCLR = ~ Ddata;
//delay_ms(5);
datawrt();
//delay_ms(5);
----------------------------------------- LCD string display ----------------------------------------
void lcd_string (char *senpoint)
while (*senpoint != '\0')
lcd_char(*senpoint);
//delay_ms(5);
senpoint++;
--------------------------------------- ADC Conversion -------------------------------------------
floatToString(float Gfltfs_temp)
Gfltfs_temp = Gfltfs_temp;
OUTPUT1[0] = Gfltfs_temp /1000 + '0';
Gfltfs_temp = (int)Gfltfs_temp % 1000;
OUTPUT1[1] = Gfltfs_temp /100 + '0';
Gfltfs_temp = (int) Gfltfs_temp % 100;
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OUTPUT1[2] = Gfltfs_temp /10+ '0';
Gfltfs_temp = (int)Gfltfs_temp % 10;
OUTPUT1[3] = Gfltfs_temp + '0';
OUTPUT1[4] = '\0';
-------------------------------------- Line Address commd ------------------------
void lcd_line3_m(void)
lcd_cmd(0x9f);
void lcd_line2_m(void)
lcd_cmd(0xca);
void lcd_line1_m(void)
lcd_cmd(0x88);
/---------------------------LCD line 4 Initialization -------------------------------/
void lcd_line4(void)
lcd_cmd(0xd4);
//delay_ms(5);
/---------------------------LCD line 3 Initialization--------------------------------/
void lcd_line3(void)
lcd_cmd(0x94);
//delay_ms(5);
/---------------------------LCD line 2 Initialization----------------------------------/
void lcd_line2(void)
lcd_cmd(0xc0);
//delay_ms(5);
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/----------------------------LCD line 1 Initialization------------------------------------/
void lcd_line1(void)
lcd_cmd(0x80);
//delay_ms(5);
/------------------------------------------LCD display 1 function------------------------/
void lcd_display1(void)
// lcd_line1();
lcd_cmd(0x80);
//delay_ms(5);
lcd_string(" PA GAS ANALYZER ");
//delay_ms(5);
//lcd_line2();
lcd_cmd(0xc0);
//delay_ms(5);
lcd_string("PA Signal-");
//delay_ms(5);
/-----------------------------------------LCD display function------------------------------/
void lcd_display2(void)
lcd_line3();
//lcd_cmd(0x99);
//delay_ms(5);
lcd_string("Concent -");
//delay_ms(5);
lcd_line4();
//lcd_cmd(0xd6);
//delay_ms(5);
lcd_string("Tempertr -");
//delay_ms(5);
/-------------- Concentration of Air pollutant display function------------/
void lcd_display3(void)
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delay_ms(5);
lcd_cmd(0xCB);
//delay_ms(2);
DIGITAL_DATA1=IOPIN;
Gfltfs_temp=(float)RESOL* DIGITAL_DATA1*1000;
floatToString(Gfltfs_temp);
lcd_string(OUTPUT1);
lcd_string(" mV ");
lcd_cmd(0x9F);
floatToString(Gfltfs_temp/1.2);
lcd_string(OUTPUT1);
lcd_string(" PPM ");
/----------------------------------Temperature display function--------------------/
void lcd_display4(void)
delay_ms(5);
lcd_cmd(0xDF);
DIGITAL_DATA2=0X0e65;
Gfltfs_temp=(float)RESOL*DIGITAL_DATA2/10 *1000;
floatToString(Gfltfs_temp);
lcd_string(OUTPUT1);
lcd_string(" oC ");
/-------------------------------------------LCD display function---------------------------/
void lcd_display(void)
lcd_display1();
lcd_display2();
while (1)
lcd_display3();
lcd_display4();
//lcd_cmd(0x01);
/---------------------------------------LCD Initialization-------------------------------------/
void lcd_int(void)
lcd_cmd(LCD_INIT); //set 8-bit mode and 2 lines
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lcd_cmd(LCD_INIT);
lcd_cmd(DispOn_CursorBlink); //display on - cursor blink on
lcd_cmd(ClrDisplay); //clear display
lcd_cmd(CursrRightShift); //cursor move & shift right
delay_ms(5);
/----------------------------LCD clock Initialization ---------------------/
void clk_int(void)
PLLCON =0x00; // Disenable and disconnect the PLL
delay_ms(5);
PLLFEED=0xAA;
delay_ms(5);
PLLFEED=0x55;
delay_ms(5);
/------------------------------------Main program start------------------------------------/
int main(void)
delay_ms(300);
clk_int();
PINSEL0 = 0x00000000;
PINSEL1 = 0x00000000;
IODIR = 0xFFFFFFFF;
IOCLR = 0xFFFFFFFF;
IOSET = Latch;
lcd_int();
while(1)
lcd_display();
/---------------------------------------Program end -------------------------------------------/
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Section 3.4
CALIBRATION AND MEASUREMENT PROCEDURE
The individual blocks of the embedded based photoacoustic system for the
measurement of air pollutants are designed and constructed. The necessary software is
developed in embedded C language. The software details are already discussed. Before
using the photoacoustic system for real samples, the system must be calibrated by
measuring a series of known standard gas samples. In the present study, the system is
calibrated using the standard samples obtained from Chemtron Science Laboratories
Pvt. Limited, Mumbai, INDIA. Initially the software program of photoacoustic system
is run for calibration. After the execution of the program, the photoacoustic system
measurements are displayed on LCD display as shown below
(vi) Air pollutant concentration measurement.
(vii) Temperature measurement.
(viii) Pressure measurement.
The measurement procedures are also needed to consider in advance of making any
measurements. The measurement procedures of photoacoustic system are mentioned as
follows.
Clean the Photoacoustic (PA) resonance cell and keep it dry.
Connect the PA cell and Laser source to the electronic circuit.
Close inlet and outlet valves of PA cell tightly.
Purge the PA cell with nitrogen gas.
Switch ON the system and activate the software.
Switch ON the laser source in electronic modulation mode.
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Fill the sample gas into PA cell according to the required pressure.
The system measures and displays the concentration of the sample along
with pressure and temperature.
Repeat the steps from 4 to 8.
Note the readings of the air pollutants concentration along the temperature and
pressure.
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REFERENCES
1 S Michel Pont, “Programming Embedded Systems”, Addison Wesley
Publications, University of Leicester (2003).
2 E Balaguruswamy, “Programming in ANSI C” 2nd
Edition, TATA McGraw Hill
Publishing Company Limited, New Delhi (1998).
3 The User Manual, C cross Compiler, V7.2, Altium Publishers (2006).
4 K V K Prasad, “Embedded/Real-Time Systems”, Dream Tech Publishers, India
(2009).
5 The Keil Cross Compiler, ARM Company (Website: www.keil.com).
6 Yashavant Kanethkar, “Let Us C”, 5th Edition, BPB Publications, New Delhi
(2003).
7 The Training Manual of Chltenham Training Program, Gloucestershine, UK
(1998).
8 Brian W Kernighan, “The C Programming Language”, 2nd
Edition, AT&T Bell
Laboratories, Murray Hill, New Jersy (1998).
9 The Integrated Development Environment, ARM Company
(Website:www.keil.com/arm/asp).
10 IC LPC2106 32-bit Microcontroller, Datasheet, Philips Electronics, USA (2004).
11 Flash Programmer, "LPC2000 Flash Utility", Version 2.1, Philips
Semiconductors, USA (2003).
12 IC MAX232 Driver/Receiver, Datasheet, Maxim Integrated Products,
Sunnyvale, CA (1999).
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CHAPTER 4
Standardization of Embedded based
Photoacoustic Measurement System
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Section 4.1
INTRODUCTION TO STANDARDIZATION
The embedded based photoacoustic system for the measurement of air pollutants in
automobile and industrial emissions is designed and constructed in the present study.
The various concentrations of calibrated nitrogen dioxide samples are used to
standardize the embedded based photoacoustic measurement system.
For standardization1
of the photoacoustic measurement system, a diode pumped
solid-state laser source SDL-532 is used as a light source which is the maximum single
frequency and output of 20mW centered at 532nm wavelength. A square wave generator
is used to modulate(2,3)
the laser source at fixed frequency which is specially designed by
XR2206 Integrated circuit. The same modulating frequency is used to the lock-in
amplifier as a reference signal. The photoacoustic resonant cell4 is used to generate the
acoustic signal5 which is detected by microphone. The acoustic signal is applied to the
pre-amplifier6. An amplified signal is given to the lock-in amplifier. The lock-in
amplifier is specially designed to eliminate the noise in photoacoustic detection system.
The lock-in amplifier output is used to the analog to digital converter which is converted
analog signal into digital data. The digital data is applied to the microcontroller. The
microcontroller is used to process the data and display the resultant data on LCD
display. The standard NO2 samples are used to standardize the developed photoacoustic
measurement system.
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Section 4.2
RESPONSE OF THE PHOTOACOUSTIC RESONANT CELL
The frequency response7 of photoacoustic resonant cell is required to study before the
standardization of the photoacoustic measurement system. In present study, the acoustic
resonant characteristics are determined with the air sample. The air sample is injected
into photoacoustic resonant cell which is tested with a simple loudspeaker at room
temperature. The loudspeaker is kept very close to one of the windows place of the
photoacoustic resonant cell. The signal of frequency 100Hz to 4000Hz is applied to the
loudspeaker from a function generator in steps of 100 Hz. The audio signal response is
obtained from the microphone detectors in photoacoustic resonant cell. The response of
the PA cell is plotted in the graph against applied frequency of loudspeaker. The
resonant frequency is clearly seen with very slight variation induced by the influence of
other aspects like buffer volume, inlet port, outlet port and microphone holes which tend
to distort the resonance profile.
The resonant frequency characteristics of photoacoustic resonant cell are studied
using a simple loudspeaker. The maximum resonant frequency is obtained at 2055 Hz of
speaker frequency which is shown in Fig. 4.1.
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Table 4.1 : Frequency response of photoacoustic resonant cell using a loudspeaker
S. No
Frequency (kHz)
PA amplitude (Volts)
1 0.10 0.152
2 0.20 0.176
3 0.30 0.176
4 0.40 0.176
5 0.50 0.184
6 0.60 0.184
7 0.66 0.250
8 0.70 0.192
9 0.80 0.192
10 0.90 0.200
11 1.00 0.200
12 1.10 0.224
13 1.20 0.224
14 1.30 0.236
15 1.40 0.248
16 1.50 0.262
17 1.60 0.263
18 1.70 0.265
19 1.85 0.360
20 1.90 0.550
21 1.95 0.860
22 2.00 1.100
23 2.05 1.180
24 2.10 0.700
25 2.30 0.320
26 3.00 0.240
27 4.00 0.180
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Section 4.3
STANDARDIZATION OF THE SYSTEM WITH NITROGEN DIOXIDES
Standard nitrogen dioxide (NO2) gas samples of various concentrations such as 10ppm,
100ppm, 500ppm and 1000ppm obtained from Chemtron Science Laboratory, Mumbai,
India are used for standardization. The experimental setup for measurement of standard
samples is shown in Fig. 4.2.
Measurement Procedure
22. Clean the Photoacoustic resonant cell and keep it dry.
23. Connect the PA cell detectors to the electronic circuit.
24. Select TTL modulation mode of laser source8.
25. Switch ON the hardware system and activate the software.
26. Switch ON the laser source and align the beam to resonant cell.
27. Purge the PA cell with nitrogen gas.
28. Fill the sample gas into PA cell according to the required pressure.
29. Close inlet and outlet valves of PA cell tightly.
30. The system detects, measures and displays9 the gas concentration along with
temperature10
and pressure.
31. Repeat the steps from 6 to 9.
32. Note the readings and draw the graph of PA amplitude as a function of sample
concentration.
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The various concentrations of nitrogen dioxide are tested and results are shown in Figs.
4.4 to 4.7. The PA signal behavior is qualitatively in good agreement with the standard
gas samples.
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Section 4.4
STANDARDIZATION OF EMBEDDED BASED PHOTOACOUSTIC
SYSTEM - RESULTS AND DISCUSSION
In the present study, various standard concentrations of nitrogen dioxide are chosen for
the standardization of an embedded based photoacoustic measurement system. The
standard NO2 samples - 10 ppm, 100 ppm, 500 ppm and 1000ppm are collected from
Chemtron Science Laboratory, Mumbai, India. The concentration of nitrogen oxides of
these standands are measured with the designed and developed in present study. The
results of the measurements are presented in Table 4. 8. These measurements are also
made with the Standard Gas Analyzer, Model No.T200H used in Ramky Laboratory,
Hyderabad. The results are presented in the same table for comparison. The individual
results of measurements of standard gases are also presented in Tables 4.4 to 4.7 and
Figs. 4.4 to 4.7.
The baseline of the system is also tested with the nitrogen sample which has
almost stable baseline throughout the range of modulating frequencies. The baseline
profile is shown in the Fig. 4.3. All samples are tested at constant pressure 20kPa and at
room temperature10
. The system is quite successful in the measurement of nitrogen
dioxide in the given standard samples with an accuracy of ±1ppm.
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Table 4.3 : Baseline measurement of nitrogen sample
S. No
Frequency (kHz)
PA amplitude (mV)
1 0.20 0.36
2 0.30 0.40
3 0.40 0.42
4 0.50 0.40
5 0.60 0.44
6 0.66 0.52
7 0.70 0.39
8 0.80 0.40
9 0.90 0.40
10 1.00 0.39
11 1.10 0.40
12 1.20 0.42
13 1.30 0.41
14 1.40 0.42
15 1.50 0.40
16 1.60 0.41
17 1.70 0.43
18 1.80 0.46
19 1.90 0.50
20 2.00 0.60
21 2.05 0.70
22 2.10 0.66
23 2.50 0.43
24 3.00 0.40
25 4.00 0.39
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Table 4.4 : Measurement of standard NO2 (10ppm)
S. No
Frequency
(kHz)
PA Amplitude
(Volts)
1 0.10 0.0030
2 0.20 0.0030
3 0.30 0.0040
4 0.40 0.0050
5 0.50 0.0040
6 0.66 0.0055
7 0.70 0.0050
8 0.80 0.0040
9 0.90 0.0040
10 1.00 0.0040
11 1.50 0.0040
12 1.60 0.0040
13 1.70 0.0040
14 1.80 0.0040
15 1.90 0.0040
16 1.95 0.0070
17 2.00 0.0130
18 2.05 0.0170
19 2.10 0.0140
20 2.20 0.0050
21 2.50 0.0040
22 3.00 0.0040
23 4.00 0.0040
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Table 4.5 : Measurement of standard nitrogen dioxide (100 ppm)
S. No Frequency
(kHz)
PA amplitude
(Volts)
1 0.10 0.012
2 0.20 0.012
3 0.30 0.012
4 0.40 0.015
5 0.50 0.013
6 0.66 0.029
7 0.60 0.016
8 0.70 0.012
9 0.80 0.015
10 0.90 0.014
11 1.00 0.010
12 1.60 0.012
13 1.70 0.014
14 1.80 0.015
15 1.90 0.020
16 1.95 0.024
17 2.00 0.050
18 2.02 0.112
19 2.05 0.182
20 2.08 0.110
21 2.10 0.034
22 2.30 0.020
23 2.50 0.019
24 3.00 0.013
25 4.00 0.014
26 5.00 0.013
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Table 4.6 : Measurement of standard nitrogen dioxide (500ppm)
S. No Frequency (kHz) PA amplitude (Volts)
1 0.10 0.06
2 0.20 0.06
3 0.30 0.06
4 0.40 0.07
5 0.50 0.08
6 0.66 0.10
7 0.60 0.08
8 0.70 0.06
9 0.80 0.08
10 0.90 0.07
11 1.00 0.05
12 1.60 0.06
13 1.70 0.07
14 1.80 0.08
15 1.90 0.10
16 1.95 0.12
17 2.00 0.25
18 2.02 0.56
19 2.05 0.86
20 2.08 0.60
21 2.10 0.17
22 2.30 0.10
23 2.50 0.09
24 3.00 0.09
25 4.00 0.07
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Table 4.7 : Measurement of standard nitrogen dioxide (1000ppm)
S. No Frequency (kHz) PA amplitude (Volts)
1 0.10 0.121
2 0.20 0.121
3 0.30 0.128
4 0.40 0.152
5 0.50 0.136
6 0.66 0.296
7 0.60 0.163
8 0.70 0.128
9 0.80 0.156
10 0.90 0.144
11 1.00 0.104
12 1.60 0.128
13 1.70 0.144
14 1.80 0.152
15 1.90 0.200
16 1.95 0.248
17 2.00 0.502
18 2.02 1.120
19 2.05 1.720
20 2.06 1.000
21 2.10 0.340
22 2.50 0.200
23 3.00 0.196
24 4.00 0.136
25 5.00 0.144
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Table 4.8 : Measurement of NO2 samples at various concentrations
*Gas Analyzer Model No. T200H, Teledyne, Instruments, CA, USA.
S. No
Input standard
NO2 concentration
(ppm)
Present study
Standard Gas
Analyzer*
(ppm)
Corresponding
output
(Volts)
1 10 9.80 9.85 0.017
2 100 98.50 99.20 0.182
3 250 247.00 248.40 0.450
4 500 496.00 498.00 0.870
5 750 745.50 747.00 1.320
6 1000 989.00 993.50 1.720
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REFERENCES
17. K M Adams, Applied Optics, 27, 4052 (1988).
18. Frank Muller, Alexander Popp and Frank Kuhnemann, Optical Society of
America, 11, 2820 (2003).
19. C Haisch and R Niassner, Spectroscopy Europe, 14, 11 (2002).
20. Andra Miklo´s and Peter Hess, Review of Scientific Instruments, 72, 1937
(2001).
21. Frans Harren, Gina Cotti, Jos Omens and Sacco Hekkert, “Photoacoustic
Spectroscopy in Trace Gas Monitoring”, John Wiley & Sons Publishers (2006).
22. IC INA163 Low Noise Preamplifier, Datasheet, Texas instruments company,
Texas (2005).
23. Harren, Bijnen and Reuss, Applied physics, 50, 137, Netherlands (1990).
24. DPSS Laser (SDL-532-020), Shanghai Dream Lasers Technologies Co., Ltd,
China.
25. LCD module (FDCC2004), Datasheet, FORDATA Electronic corporation
Limited, China.
26. IC LM35 Precision Centigrade Temperature Sensor, Datasheet, National
Semiconductors (2000).
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CHAPTER 5
Measurement of Nitrogen Oxides in
Industrial Emissions
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Section 5.1
INDUSTRIAL EMISSIONS
India is one of the ten most industrialized nations of the world. But this status
has risk of accidents. Industrial emissions are rapidly increasing in India. These
pollutants are usually harmful to the health of human beings, animals, plants and
environment. brought with it unwanted and unanticipated consequences such as
unplanned, industrialization, urbanization, air pollution1 and the risk of accidents.
Industrial emission are rapidly increasing in india.
Seven categories of industries in Andhra Pradesh such as pharma industries,
cement plants, thermal power plants, oil refineries, petrochemicals, integrated iron and
steel plants, pesticides and fertilizer units are identified as significant air polluting
industries. These industries are distributed in Hyderabad, Ranga Reddy, Medak and
Visakhapatnam areas. The list of industries in Hyderabad, Ranga Reddy district area is
given in Table 5.1. The pharma sector has the maximum number of industries followed
by thermal plants, cement and fertilizer plants. It indicates that pharma-based and
process industries have major shares of 45% and 32% of the total number of industries
respectively.
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Table 5.1 : List of industries in Hyderabad and Ranga Reddy districts
S. No. Name of industry Type of industry District
1 Mylan Pharma Pharmaceutical Ranga Reddy
2 Aurobindo Pharma Limited Pharmaceutical Hyderabad
3 Zenotech Labs Ltd. Pharmaceutical Hyderabad
4 Dr. Reddy’s Laboratory Pharmaceutical Hyderabad
5 Divis Laboratory Ltd. Pharmaceutical Hyderabad
6 SMS pharmaceutical Pharmaceutical Hyderabad
7 Gulf oil corporation Process Ranga Reddy
8 Natco Pharma Pharmaceutical Hyderabad
9 Matrix Laboratory Ltd. Pharmaceutical Ranga Reddy
10 Aptuit Laurus Ltd. Pharmaceutical Hyderabad
11 Hyderabad rubber products Rubber plant Hyderabad
12 Genix Pharma Ltd. Pharmaceutical Hyderabad
13 Gland pharma Ltd Pharmaceutical Ranga Reddy
14 Glochem industries Pharmaceutical Hyderabad
15 Hetero drug Ltd. Pharmaceutical Ranga Reddy
16 Neuland Laboratories Ltd. Pharmaceutical Hyderabad
17 SH Pharma Ltd. Pharmaceutical Hyderabad
18 Agri-lifie Fertilizer plant Ranga Reddy
19 Erythro Pharma Pvt. Ltd. Pharmaceutical Hyderabad
20 Indian Genomix Pvt. Ltd. Pharmaceutical Hyderabad
21 Joflo industries Pharmaceutical Ranga Reddy
22 Ravoos Laboratory Ltd. Pharmaceutical Ranga Reddy
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23 Saraca Laboratories Ltd. Pharmaceutical Hyderabad
24 Thermax industries Power plant Ranga Reddy
25 Vamshi rubber Limited Rubber plant Hyderabad
26 ATS GeneTech Pvt.Ltd. Pharmaceutical Hyderabad
27 Co-Gen power plant Power plant Hyderabad
28 Likhitha industries Process plant Hyderabad
29 Rastria chemical & fertilizer Ltd. Chemical plant Ranga Reddy
30 RCC Lab. India Ltd. Pharmaceutical Hyderabad
31 Suven Life Sciences Ltd. Pharmaceutical Hyderabad
32 Pains industries Process Ranga Reddy
33 Hyderabad Chemical
Products Ltd.
Chemical plant Ranga Reddy
34 Nayagara Industries Ltd. Process plant Ranga Reddy
35 Poly Hi Solidur Plastics
India Ltd.
Plastic plant Ranga Reddy
The following are the major air pollutants of these industrial emissions.
• Nitrogen oxides
• Carbon soot
• Carbon monoxide
• Sulphur dioxides
• Carbon dioxide
• Volatile organic components etc.
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Section 5.2
NITROGEN OXIDES POLLUTANT
Nitrogen oxides (NOx) are a mixer of nitric oxide (NO) and nitrogen dioxide (NO2). It
is one of the most prominent air pollutants and a poison by inhalation. NOx is a reddish-
brown, pungent and acidic gas which is strongly corrosive. The combustion of fuel such
as coal, gasoline and oil engines produces NOx pollutant. NOx is generating usually
from reaction of nitrogen and oxygen atoms during combustion process at high
temperatures. The oxygen and nitrogen do not react at ambient temperatures, but they
can react at high temperatures and produce various oxides of nitrogen into atmosphere
which are as follows.
N2 + O2 → 2NO
2O2 + N2 → 2 NO2
In most of the cities, the industries and motor vehicles contribute high amount of
nitrogen oxides in the atmosphere. The industries and motor vehicles such as thermal
power plants, pharmaceutical industries, rubber industries, diesel engine generators,
diesel motor vehicles etc. are contributing about 80% of ambient nitrogen dioxides in
the city environment. Nitrogen dioxide is also produced from the industrial processes of
nitric acid, metals, welding, refining of petrol and explosives. The main source of
nitrogen oxides is the result of industrial activities2. The emissions of nitrogen oxides
(3-
5) from various fuels used in the industries are presented in the Table 5.1.
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Table 5.2: Emission levels of nitrogen oxides from various fuels
S. No Name of Fuel
Emission of NOx
(g/kg fuel)
1 Oil 3.0
2 Kerosene 3.0
3 Coal 4.5
4 Propane 2.3
5 Gasoline 27.0
6 Natural Gas 1.0
7 Butane 2.3
8 Wood 0.7
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Effects on health
The NOx is a poison by inhalation. The long-term exposure to NOx at concentrations
above 100µg/m³ causes adverse health effects. Nitrogen dioxide irritates the lungs and
lower resistance to respiratory infections6 such as flu and grippe. The effects of short-
term exposure are still unclear, but continued exposure to concentrations is typically
much higher than those normally found in the ambient air. Children are more sensitive
to the effects of nitrogen oxides. The health effects in children are as follows
• Short-term exposure to NOx concentrations (>3 ppm) can decrease lung
function.
• Frequent exposure to low concentrations (<3 ppm) can irritate lungs.
• Concentrations as low as 0.1 ppm cause lung irritation and measurable decreases
in lung function in asthmatics.
• Long-term exposures to lower level concentration can destroy lung tissue and
lead to emphysema.
Effect on the environment
Nitrogen oxides contribute to form ozone7 and can have adverse effects on both
terrestrial and aquatic ecosystems. Nitrogen oxides in the air can significantly contribute
to anumber of environmental effects such as acid rain and biological process in coastal
waters. In biological process, the body of water suffers with nutrients. NOx leads to
reduce in the amount of oxygen in the water and environment which is destructive to
fish and other animal life.
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Effects on visibility
Nitrogen oxides can form secondary particles which are called nitrates. It causes haze
and reduces visibility. Nitrogen oxides make summer smog which looks like brownish
in colour.
Thus the nitrogen oxides of these industrial emissions need to be monitored and the
measures to reduce them are to be initiated. Hence, in the present study, it is proposed to
measure the concentration of nitrogen oxides of the industrial emissions of
pharmaceutical and process industries of Hyderabad and Rangareddy districts in Andhra
Pradesh with the instrument developed in the present study.
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Section 5.3
EXPERIMENTAL PROCEDURE
The following experimental procedure is followed in the measurement of nitrogen
oxides from the industrial emissions.
1. Clean the photoacoustic resonant cell and keep it dry.
2. Connect the PA cell detectors to the electronic circuit.
3. Select the laser source and use in modulation mode.
4. Switch ON the hardware system and activate the software.
5. Switch ON the laser source and align the beam to resonant cell.
6. Purge the PA cell with nitrogen gas.
7. Fill the standard gas sample gas into PA cell according to the required pressure.
8. Close inlet and outlet valves of PA cell tightly.
9. The measurement system measures and displays the gas concentration along
with temperature and pressure.
10. Repeat the steps from 6 to 9.
11. Note the readings of photoacoustic measurement system.
The experimental arrangement is already described in chapter 2.
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Section 5.4
MEASUREMENT OF NITROGEN OXIDES OF INDUSTRIAL
EMISSIONS RESULTS AND DISCUSSION
The pharmaceutical and process industries of Hyderabad and Ranga Reddy districts as
indicated in Table 5.3 are chosen for the measurement of nitrogen oxides of the
industrial emissions. The samples are collected from these industries. The concentration
of nitrogen oxides8 of these industrial emissions are measured with the system designed
and developed in the present study. The results of the measurements are presented in
Table 5.4. These measurements are also made with the Standard Gas Analyzer, Model
No.T200H used in Ramky Laboratory, Hyderabad. The results are presented in the same
Table for comparison. The results of the present study are in good agreement with those
values obtained from the standard gas analyzer. The range of these measurements is
1ppm to 1000ppm with the deviation error of ±1%.
The industrial emission samples from Aurobindo pharma, Dr. Reddy’s pharma
and Hyderabad rubber plant have very high nitrogen oxide levels. The emission samples
from Thermax industries contain high concentration of nitrogen oxides. The emission
samples from Gulf oil corporation, Likhita industries, and Mylan pharma are having
moderate NOx and remaining three emission samples from Paint industry, Gland
pharma and Hetero drugs R&D are having below emission standards (120ppm for NOx)
of pollution control board.
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Table 5.3 : List of selected industries for measurement of nitrogen oxides
S. No. Name of industry Type of industry Location
1 Mylan pharma limited Pharmaceutical Ranga Reddy
2 Aurobindo pharma industry Pharmaceutical Ranga Reddy
3 Hetero drugs plant Pharmaceutical Hyderabad
4 Gulf oil corporation Process Ranga Reddy
5 Co-gen power plant Process Hyderabad
6 Dr. Reddy’s laboratory Pharmaceutical Ranga Reddy
7 Likhita industries Process Hyderabad
8 Paints industry Process Ranga Reddy
9 Gland pharma Limited Pharmaceutical Ranga Reddy
10 Hyderabad rubber Plant Process Hyderabad
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Table 5.4 : Measurement of nitrogen oxides of industrial emissions
S. No Name of industry,
Location
Sample
accumulated from
Present study
(ppm)
Standard Gas
Analyzer*(ppm)
1 Aurobindo Pharma
Industry,
Bachupally, Ranga
Reddy dist.
Reactor exhaust
754.5
756.2
2 Dr.Reddy’s
Laboratory,
Ranga Reddy dist.
Reactors exhaust
679.5
681.5
3 Hyderabad rubber
Plant, Hyderabad.
Exhaust pipe
629.0
630.2
4 Thermax industries,
Ranga Reddy dist.
Boiler chimney
606.7
608.4
5 Gulf oil corporation,
Hyderabad.
Boiler chimney
523.9
525.2
6 Likhita industries,
Hyderabad.
Exhaust pipe
516.5
518.4
7 Mylan pharma,
Ranga Reddy dist.
Exhaust pipe
469.0
470.3
8 Paints industry,
Ranga Reddy dist.
Chimney
314.8
315.2
9 Gland pharma,
Jeedimetla, Ranga
Reddy dist.
Chimney/ exhaust
117.2
118.1
10 Hetero drugs
plant(R&D)
Hyerabad.
Exhaust/chemney
97.6
99.7
*Gas Analyzer Model No.T200H, Teledyne Instruments, CA, USA
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REFERENCES
1. Aaron Daly and Paolo Zannetti “An Introduction to Air Pollution- Definitions,
Classifications and History”, The EnviroComp Institute, Fremont, USA (2007).
2. Mark Jacobson, Journal of Geophysical Research, 115, 78 (2010).
3.Schramm, Sthel and Da Silva, Infrared Physics & Technology, 44, 263 (2003).
4.Nancy Marley and Jeffrey Gaffney,” New improved Fast GC-Luminol Instrument
for PAN and Nitrogen Dioxide Measurements”, Environmental Research Division
Argonne National Laboratory, Argonne, Illinois, USA(2001).
5. G J Wendel, DH Steadman, and C. A. Cantrell, Analytical Chemistry, 55, 937 (1983).
6. S Soehodh and S Taufic, Eastern Asia Society for Transportation Studies, 5,
1841 (2005).
7. A Yerramilli, V S Challa and V B R Dodla, “Simulation of Surface Ozone
Pollution in the Central Gulf Coast Region using WRF/Chem model: Sensitivity to
PBL and Land Surface Physics,” Advances in Meteorology, 2011 (2010).
8. T Brugman, “Laser Based Diagnostics on NO in a Diesel Engine”, Ph.D Thesis,
Nijmegen University (1999).
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CHAPTER 6
Measurement of Carbon Soot Pollutant
in Automobile Emissions
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Section 6.1
AUTOMOBILE EMISSIONS
One of the most concerning problems faced by the modern society is the atmospheric
pollution1, which can cause dangerous environmental consequences such as the
degeneration of air quality, acid rain, photochemical2 smog, ozone layer depletion,
health diseases and the global warming.
Several emission sources such as internal combustion engines of motor vehicles,
power plant boilers, hog-fuel boilers, central steam heat boilers, waste incineration,
local field burning, house fires, forest fires, fireplaces etc. generate huge of carbon
soon3 to the atmosphere which is the resultant of pyrolysis process. The exterior sources
such as smoking substances, oil lamps, candles, wood stoves, quartz/halogen bulbs with
settled dust, fireplaces and defective furnaces also contribute to the indoor environment.
The majority of carbon soot release from automobile emissions4 in cities. The carbon
soot forms in various size and shape during the normal combustion processes5 in diesel
engines. The rate of soot generation in automobile depends on many factors which are
as follows
• Engine type, size and configurations.
• Equipment applications, operating modes and frequencies.
• Fuel delivery and control settings.
• Intake and exhaust gas recirculation (EGR) conditions.
• Wear modes of the engine and fuel delivery components.
• Age of equipment.
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The transport is liable for a great part of the damaging soot pollutant emitted by
anthropogenic sources. The greater municipality of Hyderabad located in Andhra
Pradesh has more than seven million inhabitants. Having a great fleet of motor vehicles,
it is summarily important to evaluate automobile emissions of gases harmful to planet
and human health.
About Hyderabad City
Hyderabad, a 400 year old city is the state capital of Andhra Pradesh. It lies on the
Deccan Plateau, 541 meters (1776 ft) above sea level, over an area of approximately
650 square kilometers. Hyderabad, along with its twin city of Secunderabad, is the fifth
largest city in India, with a population nearing 8 million. Due to its prominence as a
major high-tech center, it is one of the fastest growing with a population density of
~17,000 persons per square kilometer. The rapid rate of urbanization with increased
economic activity has encouraged migration to the twin cities, which led to an increase
of personal, public, and para (3 and 6 seat autos) transit vehicles, industrial output and
increasing burden on the cities infrastructure. Hyderabad along with the surrounding ten
municipalities constitutes the Hyderabad Urban Development Authority (HUDA) and
has been growing at an average rate of 9%. Air pollution is a growing health hazard in
the city. Among the many sources of pollution, the transport sector is contributing a
significant amount of carbon soot pollution.
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Section 6.2
CARBON SOOT POLLUTANT
Carbon soot is one of the air pollutants. It is a general term that refers to impure carbon
particles resulting from the incomplete combustion of a hydrocarbon. Carbon soot is in
the general category of airborne particulate matter which is considered hazardous to the
lungs and general health, when the particles are less than five micrometers in diameter
such particles are not filtered out by the upper respiratory tract. Carbon soot emits from
various sources such as internal combustion engines, power plant boilers, central steam
heat boilers, waste incineration, local field burning, house fires, forest fires, furnaces
etc.
Characterization of carbon soot
During the last 20 years a large number of studies have allowed a better understanding
of carbon soot and its characterization(5,6)
. In spite of all these efforts a lot has still to be
learned about this unique filler. The mono unit of carbon soot is the aggregate, a sub-
micron object of complex shape. The images of carbon soot are shown in Fig.6.1 which
are taken by Transmission Electron Microscope (TEM) instrument. The type and size of
carbon soot particles7 are given in Table 6.1.
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Table 6.1: Carbon soot particle type and sizes of various exhausts
S. No Carbon soot type Size range (nm) Source of
generation
1 Acetylene flame soot 5 to 50 Flame
2 Candle flame soot 10 to 100 Flame
3 Kerosene flame soot 20 to 600 Flame
4 Diesel exhaust soot 20 to 300 Diesel generator
5 Electric arc soot 20 to 300 Palas electric arc
6 Plastic burning soot 10 to 200 Plastic bag
7 Styrofoam burning soot 10 to 200 Styrofoam
8 Wood burning soot 30 to 300 White oak
9 Rice straw burning soot 30 to 600 Rice straw
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Two kinds of soot particles are regulated by the Indian government. One is fine
soot particles (PM2.5) which are <2.5 micrometers in diameter another is coarse soot
particles (PM10) which are between 2.5 and 10 micrometers in diameter. Both particles
are smaller than the width of a human hair. The leading-edge research suggests that the
existences of even smaller particles are more damaging to health.
Hence the carbon soot of these automobile emissions needs to be monitored and
the measures to reduce them are to be initiated. Hence, in the present study, it is
proposed to measure the concentration of carbon soot of the automobile emissions of
motor vehicles of Hyderabad city in Andhra Pradesh with the instrument developed in
the present study.
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Section 6.3
CALIBRICATION AND MEASUREMENT PROCEDURE
Before using the system for measurement of carbon soot in automobile
emission(8,9)
, the system must be calibrated by measuring a series of known standard
gases. In the present study, the system is calibrated at five concentrations of standard
carbon soot gases 10mg/m3, 50mg/m
3, 100mg/m
3, 200mg/m
3 and 500mg/m
3. The
following calibration procedure is followed in the measurement of carbon soot
pollutant.
1. Clean the photoacoustic resonant cell and keep it dry.
2. Connect the PA cell detectors to the electronic circuit.
3. Select the laser source and use in modulation mode.
4. Switch ON the hardware system and activate the software.
5. Switch ON the laser source and align the beam to resonant cell.
6. Purge the PA cell with nitrogen gas.
7. Fill the standard gas sample gas into PA cell according to the required
pressure.
8. Close inlet and outlet valves of PA cell tightly.
9. The measurement system measures and displays the gas concentration along
with temperature and pressure.
10. Repeat the steps from 6 to 9.
11. Note the readings of photoacoustic measurement system.
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After making the appropriate adjustments in the hardware and following the
calibration procedure, the instrument is tested with the standard gases of carbon
soot(7,10)
. The outputs of the carbon soot measuring system are presented in Fig. 6.2.
The results of measurements are presented in Table 6.2. The measurements made are
compared with a Exhaust Gas Analyzer of Neptune Make (Model No.EGA200),
Mumbai, India and the results are presented in the same table. The results of the present
study are in good agreement with those obtained from the Gas analyzer.
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Table 6.2 : Carbon soot measurement in standard gases
S. No. Standard values
(mg/m3)
Present study
(mg/m3)
Gas Analyzer*
(mg/m3)
1 10 9.4 9.5
2 50 49.0 49.3
3 100 98.6 99.0
4 200 196.5 197.2
5 500 493.7 495.2
*Exhaust Gas Analyzer (Model No.EGA200), Neptune Equipments, Mumbai, India.
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Section 6.4
MEASUREMENT OF CARBON SOOT POLLUTANT
RESULTS AND DISCUSSION
The motor vehicles of Hyderabad as indicated in Table 6.3 are chosen for the
measurement of carbon soot of the automobile emissions. The samples are collected
from these motor vehicles. The concentration of carbon soot of these motor vehicles is
measured with the system designed and developed in the present study. The results of
the measurements are presented in Table 6.4. These measurements are also made with
the standard Exhaust Soot Analyzer (Model No. EGA200), Neptune equipments used in
Vimta Laboratory, Hyderabad. The results are presented the same table for comparison.
The results of the present study are in good agreement with those values obtained from
the standard gas analyzer.
The automobile emission samples from heavy-duty truck and passenger buses
have very high carbon soot levels. The emission samples from mini truck, seven seater
auto and city taxi vehicles comprise high concentration of carbon soot. The emission
samples from passenger auto and personal diesel car are having moderate black carbon
and remaining two emission samples from petrol car and motor cycles are having below
emission standards of pollution control board.
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Table 6.3 : List of selected motor vehicles for measurement of carbon soot
S. No.
Motor vehicle
LocationLocationLocationLocation
ManufacturerManufacturerManufacturerManufacturer 1 Heavy-duty Truck
Balanagar, Ranga
Reddy District
Ashok Leyland
2 Metro City Bus Kukatpally, Hyderabad Tata Motors
3 Ordinary City Bus Kukatpally, Hyderabad Ashok Leyland
4 Eicher (Mini truck) Chintal, Hyderabad Eicher Motors
5 Passenger Auto KPHB Colony,
Hyderabad
Mahindra
Corporation
6 City Cabs Bharath nagar,
Hyderabad
Tata Motors
7 Private Diesel Car Sanathnagar,
Hyderabad
Maruthi Suzuki
8 Passenger Auto (Four
Seater)
Balanagar, Ranga
Reddy District
Mahindra
Corporation
9 Petrol Car Sanathnagar ,
Hyderabad
Mahindra
Corporation
10 Motor Cycle Sanathnagar,
Hyderabad
Bajaj Limited
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Table 6.4: Carbon soot measurement in automobile emissions
S. No.
Test vehicle
Present study
(mg/m3)
Gas Analyzer*
(mg/m3)
1 Heavy-duty truck
432.5 433.4
2 Ordinary City Bus 385.5 386.2
3 Metro City Bus 340.6 341.1
4 Eicher (mini truck) 290.4 291.8
5 Seven Seater
Passenger Auto
253.2
254.1
6
City Cabs
227.5
228.2
7 Private Diesel Car
155.1 156.1
8 Passenger auto
(Four seater)
150.5 151.2
9 Petrol car 145.0 145.8
10 Motor cycle
115.7 116.6
*Exhaust Gas Analyzer (Model No.EGA200), Neptune Equipments, Mumbai, India.
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REFERENCES
1. Ming Zheng, T. Graham Reader, and J. Gary Hawley, Journal of Energy
Conversion and Management, 45, 883, UK (2004).
2. C. F. Bohren and D. R. Huffman, “Absorption and Scattering of Light by Small
Particles”, John Wiley & Sons Publications, New York (1983).
3. C. Haisch and R. Niassner, Spectroscopy Europe, 14, 5, Germany (2002).
4. Ichiro Asano, “Measurement Systems for Diesel Exhaust Gas and Future
Trends”, Future article, Horiba, Japan (2000).
5. Lutz Kramer, Zoltan Bozoki and Reinhard Niessner, Journal of Analytical
Sciences, 17, 46, Japan (2001).
6. Dr. M.Gerspacher, “Carbon Black Characterization”, Sid Richardson Carbon Co.
Publishers, Texas, USA(1998).
7. W. Patrick Arnott, Hans Moosmuller, and John W. Walker, Review Science
Instrumentation, 71, 4545, USA (2000).
8. Dr. Sharad Gokhale, “Air Pollution Sampling and Analysis”, Laboratory
Manual, IIT of Guwahati, India (2009).
9. W. P. Arnott, H. Moosmuller, C. F. Rogers, T. Jin Bruch, Atmospheric
Environment, 33, 2845 (1999).
10. Hayri Serhat Sapmaz, “Soot Measurements in Steady and Pulsed Ethylene/Air
Diffusion Flames Using Laser Induced Incandescence”, Electronic Thesis and
Dissertations, Florida International University, USA (2006).
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CHAPTER 7
Measurement of Carbon Monoxide Pollutant in
Industrial and Automobile Emissions
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Section 7.1
INDUSTRIAL AND AUTOMOBILE EMISSIONS
Industries play an important role in the process of economic development in the
country. They enhance the economic welfare1 of citizens and supplies the material
goodsthey consume. The way in which society will develop in the future is largely
dependent on how the growth which industry generates in distributed. Industry is also a
major consumer of natural resources2 and a major contributor to the overall pollution
load. The relative contribution to the total pollution load is obviously higher for
industry-related pollutants. The industry sector emits both traditions air pollutants
(NOx, SOx, Organic substances and particulate matter) and newly-recognized pollutants
(specific toxic substances). The air pollutants of different industries emissions3 are
given in Table 7.1.
Automobile emissions are one of the greatest contributing agents of air pollution
in major cities across the globe. Driving a personal vehicle is the most polluting activity
of most citizens. The vehicle emissions4 contain a range of many toxic pollutants such
as carbon monoxide, sulfur dioxide, particulate matter, hydrocarbons, formaldehyde,
nitrogen dioxides, carbon soot and volatile organic compounds. The emission gases of
different vehicles are given in Table 7.2.
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Table 7.1: Emission gases of different industries
S. No. Industrial sector Emission gases
1 Thermal power plant NOx, SOx, CO and HC
2 Iron and Steel NOx, SOx, H2S, CO, HC and Toxic chemicals
3 Pharmaceuticals SO2, NOx and CO
4 Rubber plants NOx, SOx, CO
5 Chemicals Organic chemicals
6 Petrochemicals NOx, SOx, H2S, CO, HC and Toxic chemicals
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Table 7.2: Emission gases of motor vehicles
S. No. Motor vehicle Emission gases
1 Heavy-duty truck NOx, CO, VOCs and Carbon soot
2 Passenger vehicle (Bus) NOx, CO and Carbon soot
3 Mini truck NOx, CO, Carbon soot and VOCs
4 Passenger auto Carbon soot, CO and NOx
5 Light-duty truck (Diesel car) NOx, CO and Carbon soot
6 Motor cycle NOx, CO and VOCs
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Section 7.2
INTRODUCTION TO CARBON MONOXIDE
Carbon monoxide (CO) is a colorless, odorless and tasteless air pollutant. It is widely
known as the silent killer. Carbon monoxide is highly toxic to human beings and
animals. It consists of one carbon atom and one oxygen atom. CO is produced from
incomplete combustion of carbon-containing fuels such as gasoline, natural gas, oil,
coal and wood. The largest anthropogenic5 source of CO in the India is vehicle
emissions. The motor vehicles produce carbon monoxide about 60% nationwide. In
urban areas the percentage exceeded 80%. The other sources are including industrial
processes, non-transportation fuel combustion and wildfires.
Health effects
Carbon monoxide is dangerous because it inhibits the blood's ability to carry oxygen to
vital organs such as the heart and brain. Inhaled CO combines with the oxygen carrying
hemoglobin of the blood and forms carboxyhemoglobin6 (COHb) which is unusable for
transporting oxygen. The health effects of various concentration of carbon monoxide are
given in Table 7.3.
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Table 7.3: Health effects of various concentration of carbon monoxide
Exposure
(hours)
CO Concentration
(ppm)
Perceptible Sickness *Deadly
0.5 600 1000 2000
1 200 600 1600
2 100 300 1000
4 50 150 400
6 25 120 200
8 25 100 150
*A CO concentration of 12000 ppm is deadly after 1-3 minutes.
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Thus the carbon monoxide of industrial and automobile emissions needs to be
monitored and the measures to reduce them are to be initiated. Hence, in the present
study, it is proposed to measure the concentration of carbon monoxide of automobile
and industrial emissions of motor vehicles, pharmaceutical and process industries7 of
Hyderabad and Rangareddy districts in Andhra Pradesh with the instrument developed
in the present study.
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Section 7.3
CALIBRATION AND MEASUREMENT PROCEDURE
Before using the system for measurement of carbon monoxide in industrial and
automobile emissions, the system must be calibrated by measuring a series of known
standard gases. In the present study, the system is calibrated at seven concentrations of
standard carbon monoxide gases such as 10ppm, 50ppm, 100ppm, 200ppm, 500ppm,
1000ppm and 2000ppm. The following calibration procedure is followed in the
measurement of carbon monoxide pollutant.
1. Clean the photoacoustic resonant cell and keep it dry.
2. Connect the PA cell detectors to the electronic circuit.
3. Select the laser source and use in modulation mode.
4. Switch ON the hardware system and activate the software.
5. Switch ON the laser source and align the beam to resonant cell.
6. Purge the PA cell with nitrogen gas.
7. Fill the standard gas sample gas into PA cell according to the required
pressure.
8. Close inlet and outlet valves of PA cell tightly.
9. The measurement system measures and displays the gas concentration
along with temperature and pressure.
10. Repeat the steps from 6 to 9.
11. Note the readings of photoacoustic measurement system.
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After making the appropriate adjustments in the hardware and following the
calibration procedure, the instrument is tested with the standard gases of carbon
monoxide. The outputs of the carbon monoxide measuring system are presented in Fig.
7.1. The results of measurements are presented in Table 7.4. The measurements made
are compared with a Gas Analyzer of Fluke Corporation make (CO-220), USA are
presented in the same table. The results of the present study are in good agreement with
those obtained from the Gas analyzer.
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Table 7.4 : Carbon monoxide measurement in standard gases
S. No. Standard values
(ppm)
Present study (ppm) *CO Gas Analyzer
(ppm)
1 10 9.5 9.9
2 50 48.5 49.2
3 100 99.0 99.4
4 200 196.5 198.2
5 500 497.0 498.6
6 1000 996.5 998.0
7 2000 1989.0 1992.0
*Fluke CO-220, Fluke Corporation, USA.
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Section 7.4
MEASUREMENT OF CARBON MONOXIDE POLLUTANT
RESULTS AND DISCUSSION
The industries and motor vehicles of Ranga Reddy district and Hyderabad as indicated
in Table 7.5 and Table 7.6 are chosen for the measurement of carbon monoxide8 of the
industrial and automobile emissions. The samples are collected from these industries
and motor vehicles(9,10)
. The concentration of carbon monoxide of these samples is
measured with the system designed and developed in the present study. The results of
the measurements are presented in Table 7.7. These measurements are also made with
the standard CO Gas Analyzer (Model No.CO-220), Fluke Corporation used in Ramky
Laboratory, Hyderabad. The results are presented the same table for comparison. The
results of the present study are in good agreement with those values obtained from the
standard gas analyzer. The system is successful for the measurement of carbon
monoxide in industrial and automobile emissions with an accuracy of ±1%.
The industrial emission samples from Thermax industries and Co-gen power
plant have very high carbon monoxide levels. The emission samples from Aurobindo
pharma, Likhita industries and Gulf oil corporations contain high concentration of
carbon monoxide. The emission samples from Paints industry and Mylan pharma are
having moderate CO and remaining one sample from Gland pharma are having below
emission standards of pollution control board.
The automobile emission samples from heavy-duty truck, passengers bus and
eicher truck have very high carbon monoxide levels. The emission samples from
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personal diesel car and seven seater passenger auto comprises high concentration of
carbon monoxide. The emission samples from four seater auto and city cab are having
moderate CO and remaining two samples from petrol car and motor cycle are having
below emission standards(4,11)
of pollution control broad.
The embedded based photoacoustic system designed and developed in present
study is quite successful in the measurement of air pollutants - nitrogen oxides, carbon
soot and carbon monoxide in the given samples of industrial and automobile emissions
with an accuracy of ±1ppm.
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Table 7.5 : List of selected industries for measurement of carbon monoxides
S. No. Name of industry Type of industry Location
1 Thermax industries Process Ranga Reddy
District
2 Co-gen power plant Power plant Ranga Reddy
District
3 Aurobindo Pharma Pharmaceutical Bachupally, Ranga
Reddy District
4 Likhita industries Process Hyderabad
5 Gulf oil corporation Process Hyderabad
6 Paints industry Paints Hyderabad
7 Mylan pharma Pharmaceutical Ranga Reddy
District
8 Gland pharma Pharmaceutical Ranga Reddy
District
Table 7.6 : List of selected motor vehicles for measurement of carbon monoxides
S. No.
Motor vehicle
PlacePlacePlacePlace
ManufacturerManufacturerManufacturerManufacturer 1 Heavy-duty Truck
Balanagar, Ranga
Reddy District
Ashok Leyland
2 Metro City Bus Kukatpally, Hyderabad Tata Motors
3 Eicher (Mini truck) Chintal, Hyderabad Eicher Motors
4 Passenger Auto KPHB Colony,
Hyderabad
Mahindra
Corporation
5 City Cabs Bharath nagar,
Hyderabad
Tata Motors
6 Private Diesel Car Sanathnagar,
Hyderabad
Maruthi Suzuki
7 Passenger Auto (Four
Seater)
Balanagar, Ranga
Reddy District
Mahindra
Corporation
8 Petrol Car Sanathnagar ,
Hyderabad
Mahindra
Corporation
9 Motor cycle Sanathnagar, Hyd. Bajaj Limited
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Table 7.7 : Measurement of carbon monoxide of industrial emissions
S. No
Name of industry,
Location
Present study
(ppm)
CO Gas
Analyzer* (ppm)
1 Thermax industries,
Ranga Reddy District
1875.4 1878.6
2 Co-gen power plant 1823.0 1825.2
3 Aurobindo Pharma,
Bachupally, Ranga
Reddy District
1680.8
1682.6
4 Likhita industries,
Hyderabad.
1610.0
1612.4
5 Gulf oil corporation,
Hyderabad.
1584.0 1586.5
6 Paints industry, Ranga
Reddy District
1496.5 1498.1
7 Mylan pharma, Ranga
Reddy District
1368.5
1371.3
8 Gland pharma,
Jeedimetla, Ranga Reddy
District
1311.8
1313.2
*Gas Analyzer Model No. CO-220, Fluke Corporation, USA.
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Table 7.8: Measurement of carbon monoxide of automobile emissions
S. No.
Test vehicle
Location Location Location Location
Present study
(ppm)
CO Gas
Analyzer*
(ppm)
1 Heavy-duty truck
Balanagar,
Hyderabad
1966.0
1968.6
2 Passenger City
Bus
Kukatpally,
Hyderabad
1830.0 1831.1
3 Eicher (mini
truck)
Chintal,
Hyderabad
1730.5 1731.8
4 Seven seater
Passenger auto
KPHB
colony, Hyd.
1533.0
1534.1
5 City cabs Bharath
nagar, Hyd.
1517.5
1518.2
6 Private Diesel Car
Sanathnagar,
Hyderabad
1495.0
1496.1
7 Passenger auto
(Four seater)
Balanagar,
Hyderabad
1480.5 1481.2
8 Petrol car Sanathnagar,
Hyderabad
1354.0 1355.9
9 Motor cycle
Sanathnagar,
Hyderabad
1315.0 1316.1
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REFERENCES
1. P. Eugene, Journal of Environmental Economics and Management, 10, 112 (1983).
2. A.N. Fedorow and Konstantinov, Geography and Natural Resources, 30, 146
(2009).
3. Mark Jacobson, Journal of Geophysical Research, 115, 78 (2010).
4. Pranav Raghav Sood, Journal of Energy and Biotechnology, 33, 45, Singapur (2012).
5. Alan Robock, Reviews of Geophysics, 38, 191(2000).
6. J. Lopez-Herce , Borrego, Bustinza and Carrillo , Intensive Care Med. , 31, 1235
(2005).
7. V. Beschkov, “Pollution Control Technologies”, Pollution Control in Industrial
Proces Encyclopedia of Life Support Systems, Vol.III, Bulgaria.(2001)
8. M V L R Anjaneyulu., M Harikrishna and S Chenchuobulu, Journal of World
Academy of Science, Engineering and Technology,17, 135 (2008).
9. C.G.Teodoro, D.U Schramm and M.S. Sthel, “Photoacoustic Detection and
Moniotoring of Pollutant Gases from Urban Public Transport” International
Conference on Photoacoustic and Photothermal Phenomena, IOP Publishing,
Conference Series 214 (2010).
10. Sirajuddin Horaginamani, M Ravichandran, Journal of Science, Engineering and
Technology, 6, 13 (2010).
11. Emission Standards- India : On-Road Vehicles and Engines”, Dieselnet.com,
(2009).
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LIST OF PUBLICATIONS AND PRESENTATIONS
1. M. Lakshmi Prasad, K. Malakondaiah and Ramesh Datla, “Design and Fabrication
of the Differential Photoacoustic Resonant Cell for Trace Gas Analysis” Jl. of
Instrum. Soc. Of India, Vol. 39, 231 (2009).
2. M. Lakshmi Prasad, K. Malakondaiah and Ramesh Datla, “Design and Development
of Photoacoustic Spectroscopy for Detection of NO2 using Compact Low Power
DPSS Laser”, International Pitcon Conference, Chicago, USA (2009).
3. M. Lakshmi Prasad, K. Malakondaiah and Ramesh Datla, “Design and Fabrication of
The Differential Photoacoustic Resonant Cell for Trace Gas Analysis” National
Symposium on Instrumentation (NSI) , Visakhapatnam, India (2008).
4. M. Lakshmi Prasad, K. Malakondaiah and Ramesh Datla, “Development of Laser
Based Photoacoustic Gas Analyser for Detection of Environmental Poollutants”,
International Eastern Analytical Symposium, New Jersey, USA (2010).
5. M. Lakshmi Prasad, K. Malakondaiah and Ramesh Datla, “Fabrication of the
Photoacoustic Resonant Cell for Gas Analysis” International Pitcon Conference, USA
(2010).