Student
:
SEBASTIAN LEE
Matric ID No.
:
183020372
Semester
:
November 2019 – February 2020
Program
:
AME 302
Lecturer
:
Mdm. Noorradiyah binti Ismail
Submission Date :
20th of February, 2019 (Week 14)
Table of Contents
Index
Subject
Page No.
A
Table of Contents
i
1
Introduction / Research Background
1
2
Aim and Objectives
2
2.1
Aim of Research
2.2
Project Objectives
3
Overview
3
3.1
General Facts and Figures
3.2
Mechanism / Working Principle and the Elements
4
Properties, Characteristics and Specifications
4.1
Chemical Composition
4.2
Physical and Mechanical Properties
11
5
Discussion
14
6
Conclusion
15
B
References
ii
B1
Reference List
B2
Bibliography
i
1 | INTRODUCTION
Like any other academic fields or faculties, a comprehensive research that correlates with a
specific scope or area of study that is attributed to the course is part and parcel of tertiary level education.
This is no exception for the module Measurements and Instrumentations [MECH 3003] that I as a
Bachelor’s Degree in Mechanical Engineering (Hons.) student of the halls of ivy Infrastructure
University Kuala Lumpur (IUKL) was giving chase to. The assessment requirement of this module gives
rise to this merited paperwork which is an output of cumulative tutor’s pedagogy and holistic self-study
on electrical and electronics, and transducers thematics to boot. While class lessons may not fully cater
all of the information or theories germane to measurement methodologies and equipment as we lack the
tangible resources to peruse firsthand, in one way or another, students are always given the liberty to
learn online and explore its boundless virtual library teemed with manifold study materials and solutions
that can be accessed and browsed at the tip of our finger.
Equipped with the knowledge that I bear, I had prepared this paperwork to articulate about
numerous basic and auxiliary functional elements in a thermal power station. The backbone of my
research is mainly the Internet as I scoured the mass media for reliable secondary sources such as eencyclopedias, web articles, tutorial videos, academic reports, and product pages whereof from there I
winnowed out a dozen of promising information and then synthesized them into this report to convey
the facts and figures about the subject matter in accordance with the report objectives. This topic is
certainly a well-curated research subject as it helps link the nexuses between practical understanding and
theoretical understanding such as the computations involved that I have learned in the classroom. It is
also worth pointing out that as a Diploma-graduate of green technology and power engineering program,
it is no doubt that I am versed in this technical field as I attempted to derive my pre-existing knowledge
to corroborate the concepts and arguments presented in this paperwork.
This report essentially spells out the nuts and bolts of the said elements found in most power
plants. How these elements or components are discovered to be useful in the energy or power industry
and that they work in an interplay to complete every part of the system’s functionalities can be traced
back to the countless years of research and development by many pioneers ever since electrical energy
is first discovered. Plus, this report explains in detail the definitions of each element with respect to the
chosen industry. What’s more, readers will also dive into the brief mechanism or working principle of
the system and learn about the properties from the perspective of mechanical and chemical chasms. This
section is the core of this report as we deal with measurements and instrumentations of mechanical
engineering. Last but not least, this report also discusses findings based on my understanding and
comprehensive research of the topic without bias toward the facts sourced from the secondary sources.
1
2 | AIM AND OBJECTIVES
2.1 | AIM OF PROJECT
With respect to the research work as a whole, this course of action is focused toward discovering and
enriching students’ comprehension about basic and auxiliary functional elements in a thermal power
plant, encompassing its mechanical and chemical properties and behaviors; and the fundamental
mechanism or working principle, with the association of the knowledge garnered from Measurements
and Instrumentations course and information sourced from numerous secondary sources.
2.2 | PROJECT OBJECTIVES
Within the completion of this project, I should be able:i.
To learn and comprehend the basic and auxiliary functional elements employed in a thermal
power station, specifically on how they work and why do they work those ways in terms of
chemical and mechanical aspects, so as to relate with my study which pertains to transducer,
measurement and instrumentation system.
ii.
To interpret and present the significance of the evidence-based findings in light of what was
known about the research subject matter, and impart any new insights that emerged as a result
of the study as the discussion for this paperwork, so as to think critically as a researcher and
formulate justifications to the findings without being governed strictly by the objective reporting
of information enunciated in the various literature materials sourced online through content
analysis research approach, as well as by leveraging my pre-existing purview in electrical and
electronic thematics.
iii.
To meet the requirements of the Bachelor’s Degree in Mechanical Engineering (Hons.) program
of Infrastructure University Kuala Lumpur whereby prospective graduates shall satisfy specific
Programme Learning Outcomes (PLO) as well as Course Learning Outcomes (CLO) of the
Measurements and Instrumentations module which are vital to establishing the career trajectory
and professional accomplishments as prospective practicing engineers after graduation, in line
with the two Programme Educational Objectives (PEO) as formulated by the academic program
through the implementation of this research undertaking within a stipulated time frame.
2
3 | OVERVIEW
3.1 | GENERAL FACTS AND FIGURES
To begin with, measurement in a strictly technical context, is defined as a technical process to
obtain information, namely results and readings, expressed in numbers, units, symbols, and indications
of variable physical quantities. It is done by comparing between the quantity whose magnitude is not
known and a predefined standard. Measurement involves the deployment of instruments as a physical
means of determining the value of unknown quantities or variables, and thus this brings us to
instrumentation, which is defined as the devices used in measurement systems collectively.
The applications of instrumentation systems are far-ranging, and they include, but not limited to
measurement of system parameters, controlling of processes or operations, simulation of system
conditions, experimental design studies, performing of various manipulations, testing of materials,
maintenance of standards and specifications of products, quality control, and verification of physical
phenomena or scientific theories.
The basic and auxiliary functional elements are essential components of which form the
measurement and instrumentation system. Broadly speaking, all measurement and instrumentation
systems are comprised of these two distinct entities, but in the vast majority, they coexist and engage in
a complex interplay to perform specific works in the systems. First, the basic functional elements are
elements that establish the integral parts of all instruments. They can be further stratified into three:
i.
transducer element, which senses and converts desired input such as mechanical stress or the
presence of a metallic object into a more suitable and intelligible form to be processed by the
system;
ii.
signal conditioning or intermediate modifying element, which manipulates and processes the
output of the sensing element via specific means like filtering, amplification, and isolation; and
iii.
data presentation element which imparts the information about the measurand(s) in a
quantitative form.
3
On the other hand, auxiliary functional elements are elements which may be incorporated in a
particular system depending on the type of requirement, the nature of measurement technique, and the
like. Elements that are classified as auxiliary functional elements are:i.
calibration element, which provides a built-in calibration facility;
ii.
external power element, which facilitates the working of one or more of the elements like the
transducer element, signal conditioning element, data processing element or the feedback
element;
iii.
feedback element, which controls the variation of the physical quantity that is being measured,
and it is provided in the null-seeking potentiometric or Wheatstone-bridge devices to render
them automatic or self-balancing; and lastly
iv.
microprocessor element which accommodates the manipulation of data for the purpose of
simplifying or accelerating the data interpretation, and it is always used in conjunction with
analog-to-digital converter (ADC) that is integrated in the signal conditioning element.
3.2 | MECHANISM / WORKING PRINCIPLE AND THE ELEMENTS
By and large, the fundamental working principle of basic and auxiliary functional systems are
generally the same for all measurement and instrumentation systems. All instruments contain various
parts that execute specific functions in converting a variable quantity to a corresponding indication. Any
instrument and its operation can be described in terms of such functional elements. The structure is the
same but the discrepancy lies within the input variables, throughput devices used, and the output
quantities.
Figure 3.1: General structure (block diagram) of a measurement and instrumentation system
illustrating the basic functional elements.
4
Figure 3.2: General process flow diagram of a measurement and instrumentation system
encompassing the basic and auxiliary functional elements.
Figure 3.3: Anatomy of a thermal power plant.
5
Figure 3.4 A detailed process flow diagram of a thermal power station.
1.
Transducer element
This element encapsulates all the sensing devices or transducers adopted in the thermal generating
station to receive and convert inputs in various forms of physical stimuli into outputs in other
forms before being fed and interpreted by the next element, i.e. signal conditioning element.
Table 3.1: Sensing elements (basic functional elements) typically employed in the thermal
power station.
Input
variable to
transducer
Output variable
Principle of
of transducer
operation
Type of device
Used/Installed
in
Mechanical instruments
An
electromotive
force
(emf)
is
generated across the
junctions
Temperature
Voltage
of
two
dissimilar metals or
semiconductors
when that junction is
heated based on the
Seebeck effect.
6
• Thermocouple
(J, K, R, S, E,
etc. types)
• Resistance
temperature
detector (RTD)
( Pt100, Pt1000,
JPt500 etc.)
• Boiler
• Feed water
at
economizer
inlet.
The application of
Pressure
Displacement
pressure
causes
displacement
in
elastic elements.
• C-type bourdon
pressure gauge • Boiler
• Turbine
(spherical,
helical, twisted) • Pipelines
• Manometer
• Condensate/
Differential pressure
Flow rate
• Pressure
is generated between
• Voltage
the main pipeline and
throat of the device.
• Venturi tube
• Orifice
Cooler tank
• High-
flowmeter
pressure
• Ultrasonic
steam
• Feed water
flowmeter
inlet
The
mechanical
instruments
move
corresponding to the
level
of
the
water/liquid.
For
example,
the • Bubbler tube
movement
Level
• Displacement
• Voltage
of
the • Hydra
float indicates the
drum
level and can actuate
indicator
step
level
a switch or create an • Float
output signal.
• Capacitive level
As for the capacitive
• Boiler drum
• Water line
• Condensate
tank
switch
type, capacitance is
formed between the
probe rod and the
wall
of
the
tank
which acts as ground.
For the tachometer, it
works by dint of
Speed
Voltage
motion • Stroboscope
relative
the • Tachometer
between
magnetic field and
shaft of the coupled
7
• Generator
(shaft)
• Turbine
• Recycling
pump
device.
The
developed EMF is
directly proportional
to the speed of the
shaft.
For
the
stroboscope, it uses a
flash lamp driven by
an
oscillator
to
inspect or measure
the rotational speed
of the spinning parts
whereby the flashing
light
creates
the
perception of stopmotion which is ideal
for
diagnostic
inspections
moving
of
machinery
and can be translated
into determining the
cyclic speed.
When
stress
Vibration
Voltage
mechanical
is
applied,
movement
is
detected, or latent
heat
is
electric
received,
charge
generated.
8
is
• Piezoelectric
sensor
• Turbine
• Generator
Figure 3.5: A variety of transducers of various functions found in a thermal power plant.
2.
Signal conditioning element
The outputs of the transducer element are usually too small to operate an indicator or a chart
recorder. Therefore, it is the job of this subsequent basic functional element to compensate,
modify, and optimize the imperfect signals present, thereby making them compatible for interface
by elements in the next stages.
i.
Amplification
a.
Mechanical amplifying elements – Using gears and levers to provide multiplying
effect on the input transducer signals.
b.
Hydraulic/Pneumatic amplifying elements – Incorporated in orificemeters and
venturimeters used in conjunction with in valves.
c.
Electrical amplifying elements – Employing transistors and integrated circuits (ICs)
to augment the amplitude of the transducer signals.
ii.
Signal filtration
a.
Mechanical filters – The reference junctions of the thermocouples are kept in thermos
flasks containing ice. This approach protects the system from ambient temperature
changes.
b.
Pneumatic filters – Small orifices or venturis to filter out fluctuations in pressure
signals.
c.
Electrical filters – Using simple R-C circuits to eliminate stray pick-ups due to
electrical and magnetic fields.
9
3.
Data presentation element
i.
On-line monitoring (OLM)
An OLM system is made up of a data acquisition module involving hardware and software
and a data processing module involving software implemented on a fast computer. The data
acquisition module includes signal isolation devices as well as fast sampling capabilities
(e.g., 1000 Hz).
a.
Used for on-line instrumentation and control (I&C) predictive maintenance and
troubleshooting in the plant.
b.
Used for cross-correlation flow measurement.
c.
Used for online detection of venturi fouling.
d.
Used for online detection of sensing-line blockages, voids, and leaks.
e.
Used for liquid and gas leak detection.
f.
Used for core barrel vibration measurement.
g.
Used for online measurement of temperature coefficient of reactivity.
h.
Used for monitoring the performance of pressure, level, and flow transmitters.
Figure 3.6: Data acquisition signal path for OLM.
i.
Automatic control system (ACS)
a.
Continuous monitoring
-
Refers to the change of state of input into output that occur continuously.
10
Figure 3.7: Front panel of the continuous monitoring system of a thermal power plant.
4 | PROPERTIES, CHARACTERISTICS AND SPECIFICATIONS
4.1 | CHEMICAL COMPOSITION
Table 4.1: Chemical composition and classification of fly ash from the power station.
i.
Component
Bituminous [%]
Subbituminous [%]
Lignite [%]
𝑆𝑖𝑂2
20 – 60
40 – 60
15 – 45
𝐴𝑙2 𝑂3
5 – 35
20 – 30
20 – 25
𝐹𝑒2 𝑂3
10 – 40
4 – 10
4 – 15
𝐶𝑎𝑂
1 – 12
5 – 30
15 – 40
𝐿𝑂𝐼
0 – 15
0–3
0–5
Class F flue/fly ash
The burning of harder, older anthracite and bituminous coal typically produces Class F fly
ash. This type of fly ash is pozzolanic in nature, and contains less than 10% lime (CaO).
Possessing pozzolanic properties, the glassy silica and alumina of Class F fly ash requires
a cementing agent, such as Portland cement, quicklime, or hydrated lime, with the presence
of water in order to react and produce cementitious compounds.
ii.
Class C flue/fly ash
Fly ash produced from the burning of younger lignite or subbituminous coal, in addition to
having pozzolanic properties, also has some self-cementing properties. In the presence of
water, Class C fly ash will harden and gain strength over time. Class C fly ash generally
contains more than 20% lime (CaO). Unlike Class F, self-cementing Class C fly ash does
not require an activator. Alkali and sulfate (𝑆𝑂4) contents are generally higher in Class C
fly ashes.
11
4.2 | PHYSICAL AND MECHANICAL PROPERTIES
i.
Bourdon tube
•
Differential pressure: 100,000 psi (700 MPa or 7,000 bar)
•
Tube wall thickness: 0.01 – 0.05 inches
•
Design shape / Type: C-shaped, hollow spring tube is closed and sealed at one end.
•
Main materials: Phosphor-bronze / Silicon-bronze / Beryllium-copper / Inconel / C-Cr-NiMo alloys
•
Selection of the main materials: Based upon its corrosion properties and pressure range with
regard to the process media (water, air, oil, etc.).
o For severe service applications, the case is sealed and filled with glycerine or silicone
fluid to cushion the tube and movement against damage from impact and vibration.
o For low-pressure ranges (≤ 2000 psi), phosphor-bronze is used.
o For high-pressure ranges (> 2000 psi), stainless steel and beryllium-copper are preferred.
•
Corrosion resistance: Steel has a limited service life owing to corrosion but is adequate for
oil while stainless steel alloys are used to accrue its resistance toward corrosion.
•
Moving part’s materials: Glass-polycarbonate / brass / nickel silver / stainless steel
•
Material selection for the moving part: Must have very little friction and provide stability.
•
Accuracy: ±1% of full scale.
•
Sensitivity: Lower than that of spiral and helical Bourdon tubes.
•
Resolution: Lower than that of spiral and helical Bourdon tubes.
Figure 4.1: Parts of a Bourdon tube pressure gauge.
12
Table 4.2: More mechanical properties of materials used to make C-shaped Bourdon tube.
ii.
Thermocouple
•
Type: K
•
Materials: Chromel and alumel / Ni-Cr / Ni-Al
•
Selection of the materials: For used in power plants; suitable for low-temperature
applications.
•
Temperature range (ºF): -300 – 32 / 32 – 530 / 530 – 2300
•
Cycling above and below 1800°F (1000°C), is not recommended due to EMF alteration from
hysteresis effects. Plus, it should not be used in sulfurous or alternating reducing and
oxidizing atmospheres unless protected with protection tubes.
•
The negative element is slightly magnetic. It has lower resistance in ohms per foot for the
same size positive wire.
•
No moving parts, hence less likely to get damaged.
•
Wide temperature range.
•
Relatively short response time.
•
Decent repeatability.
•
Good accuracy.
•
Low sensitivity.
•
Low voltage output.
•
Susceptible to noise.
•
Accuracy: < 0.5 ºC
13
Table 4.3: More mechanical properties of all the types of thermocouples.
5 | DISCUSSION
This section succinctly discusses the effect of the effects of various binary mixtures which consist
of CO2 and He, CO, O2 , N2 , H2 , CH4 , or H2 S which could be present from impurities in the fuel or mixed
cooling flows added intentionally to improve the supercritical carbon dioxide (S-CO2 ) power cycle in
the cooler. The effect of the binary mixtures could be beneficial depending on the specific substance as
it has been found that certain concentrations of SO2 , H2 S, and Xe can enhance the performance of an SO2 power generation cycle. Within an S-CO2 power cycle, the compressor operates near the CO2 critical
point (7.39 MPa, 30.98 ºC).
In a research, the gas and mixture properties are estimated by NIST Reference Fluid
Thermodynamic and Transport Properties Database, Version 9.1. Substances mixed with the CO2 in SCO2 cycles were described in a previous work for binary mixtures and multicomponent mixtures. Within
Table2 is the reported percent difference in cycle efficiency for a binary mixture consisting of 1 mol %
impurity of each substance compared to the pure S-CO2 . It can be seen from Table 5.1 that He has the
most detrimental effect on cycle performance, while conversely it can be seen that H2 S, Xe, and SO2 have
a favorable effect on the cycle efficiency at these conditions.
For heat exchangers, the addition of some impurity phase may be seen as a positive. For the
compressor, however, this is not the case due to shifts of the pinch point. In the case of changes in the
parameters of the cooling medium, it can affect compression because the critical point is different for
mixtures than for pure CO2 . For this reason, the optimization of power cycles is very important and the
account must be taken of potential impurities or the medium from other systems with CO2 .
14
Table 5.1: The effect of binary mixtures on S-𝐶𝑂2, recompression, precompression, and split
expansion cycle efficiency.
6 | CONCLUSION
Over the course of this research undertaking, I have put some of my knowledge in this
Measurements and Instrumentations into appreciable effect by studying about the basic and auxiliary
functional elements, i.e. transducer/sensing element, signal conditioning element, data presentation
element; and calibration element, external power element, feedback element, and microprocessor
element that are typically incorporated in a thermal-powered generating station. All of these elements
work together dynamically to account for a streamlined measurement and instrumentation system in the
generation of power.
However, one thing of paramount importance when these basic and auxiliary functional elements
are set up is material and device selections. It is unequivocally crucial to understand thoroughly the
materials to be measured so that we know what type of sensors of which input and output to use, so as
to ensure a cost-effective operation of the power plant. That is why it is imperative to learn and
understand the mechanical and chemical properties of each and every component used, as accentuated
in this report, particularly on the C-shaped Bourdon tube and type-K thermocouple. Besides, factors like
the sensing points and locations of the field instruments such as internally or externally installed must
be considered when selecting level instruments for tanks. The sensing elements are not some one-sizefits-all devices as they come in multiple degrees of accuracy, sensitivity, resolution, tolerance, range,
etc, depending on the type of applications found in the thermal power plant. Apart from that, in terms of
data presentation, knowing the intended outputs, we must also be wise in choosing and setting up the
appropriate data acquisition system and control system for monitoring the processes as well as procuring
readings for production, quality and maintenance purposes.
It is my hope that the technology incorporated in most conventional thermal power plants is
progressively enhanced parallel to the Industrial Revolution 4.0 vision which is a holy grail to many
production and manufacturing industries.
15
REFERENCES
Reference List (Internet)
i.
Teeyha, Y. (2014, June 25). Introduction to Instruments and Their Representation [PowerPoint
slides]. SlideShare. Retrieved from https://www.slideshare.net/YuyuTeeyha/chapter-1-new36298700 on February 18, 2020.
ii.
Sant Longowal Institute of Engineering and Technology. (2014, June 28). Thermal power plant
layout
[PowerPoint
slides].
SlideShare.
Retrieved
from
https://www.slideshare.net/MisterKhan/thermal-power-plant-layout on February 19, 2020.
iii.
Shilpa, S. (2014, August 5). Thermal plant instrumentation and control [PowerPoint slides].
SlideShare.
Retrieved
from
https://www.slideshare.net/shilpashukla5099/thermal-plant-
instrumentation-and-control on February 18, 2020.
iv.
Ebrahim Ismaiel, Feras Saleh, Bader Alaaraj, & Neruda Barakat. (2020, January 5). Material
Types and Wall Thickness Effects on Bourdon Tube Tip Travel using Solid work. Research Gate.
Retrieved
from
https://www.researchgate.net/publication/338840391_Material_Types_and_Wall_Thickness_
Effects_on_Bourdon_Tube_Tip_Travel_using_Solidworks on February 19, 2020.
v.
John. (2011, September 13). Bourdon Tube. Instrumentation Today. Retrieved from
http://www.instrumentationtoday.com/bourdon-tube/2011/09/ on February 19, 2020.
vi.
Instrumart.
(n.d.).
About
Tachometers
/
Stroboscopes.
Retrieved
from
https://www.instrumart.com/MoreAboutCategory?CategoryID=5553 on February 18, 2020.
vii.
Nakra, B. C., & Chaudhry, K. K. (2006). Instrumentation, Measurement and Analysis. New
Delhi,
India:
Tata
McGraw-Hill
Publishing
Company
Limited.
Retrieved
from
https://tinyurl.com/spha4py on February 18, 2020.
viii.
Vesely, L., Raghu, K., Subith, V., Jayanta, S. K., Dostál, V., & Martin, S. (2018 June). Effect
of impurities on compressor and cooler performances in supercritical CO2 cycles [PDF file].
Research
Gate.
Retrieved
from
researchgate.net/publication/326522989_Effect_of_impurities_on_compressor_and_cooler_pe
rformances_in_supercritical_CO2_cycles on February 19, 2020.
ix.
Power Plant Instrumentation & Control. (n.d.). Classification of Instruments in Power Plant.
Retrieved
from
powerplantinstrumentationcontrol.yolasite.com/power-plant-details/1-
classification-of-instruments-in-power-plant on February 18, 2020.
x.
Saptarshi,
P.
(2012).
Bourdon
Tube
[PDF
file].
Scribd.
Retrieved
from
https://www.scribd.com/doc/93378791/Bourdon-Tube on February 19, 2020.
xi.
How
Products
Are
Made.
(n.d.).
Pressure
Gauge.
Retrieved
http://www.madehow.com/Volume-1/Pressure-Gauge.html on February 19, 2020.
ii
from
Bibliography (Internet)
i.
Leela, K. V. (n.d.). Functional and Operational Control of Thermal Power Plants. Academia.
Retrieved
from
https://www.academia.edu/4955076/2_Functional_and_Operational_Control_of_Thermal_Po
wer_Plants on February 19, 2020.
ii.
Vijayapriya, T. (n.d.). Functional elements of measurement system. Scribd. Retrieved from
https://www.scribd.com/document/156937143/Functional-elements-of-measurement-system
on February 18, 2020.
iii.
Ahmad Shahrizan, & Nafrizuan. (n.d.). Introduction to the sensor & instrumentation
[PowerPoint
slides].
Retrieved
from
http://ocw.ump.edu.my/pluginfile.php/13526/mod_resource/content/1/01%20TOPIC%201.pdf
on February 18, 2020.
iv.
Gaurav, R. (2017, March 5). Role of Control and Instrumentation in Thermal Power Plant
[PowerPoint slides]. SlideShare. Retrieved from https://www.slideshare.net/GauravRai80/roleof-c-i-in-thermal-power-plant on February 18, 2020.
v.
Ankur, M. (2012, February 22). Thermal power plant [PowerPoint slides]. SlideShare.
Retrieved from https://www.slideshare.net/AnkurMahajan1/thermal-power-plant-11702863 on
February 18, 2020.
vi.
WIKA.
(n.d.).
Bourdon
tube
pressure
gauge.
Retrieved
from
https://www.wika.com.my/landingpage_bourdon_tube_pressure_gauge_en_my.WIKA
on
February 19, 2020.
vii.
Ravi. (2019, April 16). Different Types of Transducers | Characteristics, Classifications,
Applications. Electronics Hub. Retrieved from https://www.electronicshub.org/types-oftransducers/ on February 19, 2020.
viii.
Inst Tools. (n.d.). Thermocouple Properties, Temperature Ranges, Element Construction.
Retrieved from https://instrumentationtools.com/thermocouple-properties-temperature-rangeselement-construction/ on February 19, 2020.
ix.
Park, R. M. (n.d.). Thermocouple Fundamentals [PDF file]. StudyLib. Retrieved from
https://studylib.net/doc/18219656/thermocouple-fundamentals on February 19, 2020.
x.
Instrumart.
(n.d.).
About
Level
Indicators
/
Controllers.
Retrieved
from
https://www.instrumart.com/MoreAboutCategory?CategoryID=6124 on February 18, 2020.
xi.
Debasis, S. (n.d.). General Principles and Representation of Instruments [PDF file]. Retrieved
from
https://nptel.ac.in/content/storage2/nptel_data3/html/mhrd/ict/text/103105130/lec4.pdf
on February 18, 2020.
iii