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PRODUCTS) ENGINEERING METROLOGY AND MEASUREMENTS (A PRACTICAL
GUIDE FOR RELIABLE PRODUCTS
Book · January 2016
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(A PRACTICAL GUIDE FOR RELIABLE PRODUCTS) Dalgobind Mahto
(A PRACTICAL GUIDE FOR RELIABLE PRODUCTS) Abstract The main purpose of Metrology is to increase awareness of
metrology and to establish a common metrological frame of
reference in terms of quality of products. It is meant to provide
easy techniques to users of different tools and techniques in
measurement with a transparent and handy tool to obtain
metrological information. Today’s global economy depends on
reliable measurements and tests, which are trusted and accepted
internationally. They should not create technical barriers to trade
and a precondition for this is a widely utilized and robust
metrological infrastructure. The content of this book is a
description of scientific, industrial and legal metrology. The
technical subject fields of metrology and metrological units are
described. A list of metrological terms is collected primarily from
internationally recognized standards. Prof.(Dr.) Dalgobind Mahto
Jaipur Institute of Engineering and Technology
Kukas, Jaipur, India Preface
It is with pleasure that we present this edition of the easy-to-use book on
Engineering Metrology and Measurements”. It is published with the sole intent of
making Diploma and degree engineering students capable in use of Engineering
Metrological tools and Measurements techniques. It is also meant to provide users
of metrology and the general public with a simple yet comprehensive reference
source on the subject. It targets those who are not familiar with the topic and who
require an introduction, as well as those who are involved in metrology at various
levels but who want to know more about the subject or simply gain specific
information. It is our hope that “Engineering Metrology and Measurements” will
make it easier to understand and work with the technical and organizational aspects
The main purpose of “Engineering Metrology and Measurements” is to increase
awareness of metrology and to establish a common metrological understanding and
frame of reference both in Europe, and between Europe and other regions
throughout the world. This is particularly important with the increased emphasis on
the equivalence of measurement and testing services for quality of life,
environmental protection and trade and in particular where technical barriers to
trade are caused by metrological impediments.
Since metrology evolves in line with scientific and technological advances it is
necessary to update and enhance “Engineering Metrology and Measurements” to
take account of this evolution. It contains more information about measurements
examples of how developments in metrology have impacted the wider world.
I hope that this edition will prove to be even more popular and widely used and
thereby contribute to a common metrological frame of reference worldwide, which
will ultimately promote good learning s in the world and improved quality of life for
its citizens. Prof. (Dr.) Dalgobind Mahto Acknowledgements
First and foremost I would like to thank God. In the process of putting this book
together I realized how true this gift of writing is for me. You given me the power to
believe in my passion and pursue my dreams. I could never have done this without
the faith I have in you, the Almighty.
I would like to thank my wife Samali for standing beside me throughout my career
and writing this book. She has been my inspiration and motivation for continuing to
improve my knowledge and move my career forward. She is my rock, and I dedicate
this book to her. I also thank my wonderful grand children: Anubha and Kashish for
always making me smile and for understanding on those weekend mornings when I
was writing this book instead of playing games with them. I hope that one day they
can read this book and understand why I spent so much time in front of my
computer. I’d like to thank my parents and grandparents for allowing me to follow
my ambitions throughout my childhood.
I’d like to especially thank Er Lalit Kumar Saraogi for trusting me and for allowing
me the freedom to manage my projects and provide the necessary time and
resource toward our applications and databases. Er Lalit Kumar Saraogi is a great
person and a scholar; without him, this book may not have been written. I think that
it will be a great asset to the community! Thanks for everything; I look forward to
writing the second edition soon! I owe a huge thanks to publisher for providing
excellent support and advice. I also wish to thank all of our technical reviewers and
our project coordinators. All of their efforts helped to make this book complete and
we couldn’t have done it without you.
Last, but definitely not least, I’d like to thank the publisher & marketing head who
has done an excellent job in leading the core of developers to produce this book and
I know that he’ll continue to do a great job leading into the future. Thanks to the
community and providing great ideas and support via the mailing lists; without this
help I could not provide the exact contents required for effective learning. Table of Contents
Sl# Chapter # Subject Content 1 Preface 2 Acknowledgements 3 Contents
Chapters 4 1 Mechanical Measurement & Metrology 5 2 Linear & Angular Measurement 6 3 Measurement of Force, Torque
and Strain 7 4 Displacement, Velocity /
Speed, and Acceleration,
easurement 8 5 Temperature Measurement 9 7 Gear Measurement 10 8 Screw Thread Measurement 11 10 Miscellaneous Metrology Page No 1
Mechanical Measurement & Metrology
1.1 Introduction 1.2 Need Of Inspection 1.3 Objectives of Metrology 1.4 Precision And Accuracy 1.5 Errors in Measurement 1.6 General Care Of Metrological
Instrument 1.7 Standardization and Standardizing Organization Department of Mechanical Engineering
Jaipur Institute of Engineering & Technology, Kukas, Jaipur Page 1.1 1. Introduction Engineering Measurement & Metrology 1.1 Introduction Metrology is a science of measurement. Metrology may be divided depending upon the
quantity under consideration into: metrology of length, metrology of time etc.
Depending upon the field of application it is divided into industrial metrology, medical
metrology etc. Engineering metrology is restricted to the measurement of length, angles and other
quantities which are expressed in linear or angular terms. For every kind of quantity measured, there must be a unit to measure it. This will enable
the quantity to be measured in number of that unit. Further, in order that this unit is
followed by all; there must be a universal standard and the various units for various parameters of importance must be standardized.
It is also necessary to see whether the result is given with sufficient correctness and
accuracy for a particular need or not. This will depend on the method of measurement, measuring devices used etc. Thus, in a broader sense metrology is not limited to length and angle measurement but
also concerned with numerous problems theoretical as well as practical related with
measurement such as:
1. Units of measurement and their standards, which is concerned with the establishment,
reproduction, conservation and transfer of units of measurement and their standards.
2. Methods of measurement based on agreed units and standards.
3. Errors of measurement.
4. Measuring instruments and devices.
5. Accuracy of measuring instruments and their care.
6. Industrial inspection and its various techniques.
7. Design, manufacturing and testing of gauges of all kinds. 1.2 Need of Inspection Inspection means checking of all materials, products or component parts at various
stages during manufacturing. It is the act of comparing materials, products or
components with some established standard. Page 1.2 Department of Engineering Engineering
Jaipur Institute of Engineering & Technology, Kukas, Jaipur Engineering Measurement & Metrology 1. Introduction In old days the production was on a small scale, different component parts were made
and assembled by the same craftsman. If the parts did not fit properly at the time of
assembly, he used to make the necessary adjustments in either of the mating parts so
that each assembly functioned properly. Therefore, it was not necessary to make similar parts exactly alike or with same accuracy
as there was no need of inspection. Due to technological development new production techniques have been developed.
The products are being manufactured on a large scale due to low cost methods of mass
production. So, hand fit method cannot serve the purpose any more. The modern
industrial mass production system is based on interchangeable manufacture, when the
articles are to be produced on a large scale. In mass production the production of complete article is broken up into various
component parts. Thus the production of each component part becomes an
independent process. The different component parts are made in large quantities in
different shops. Some parts are purchased from other factories also and then assembled
together at one place. Therefore, it becomes essential that any part chosen at random
should fit properly with any other mating parts that too selected at random. This is
possible only when the dimensions of the component parts are made with close
dimensional tolerances. This is only possible when the parts are inspected at various
stages during manufacturing. When large number of identical parts are manufactured on the basis of
interchangeability if their dimensions are actually measured every time lot of time will
be required. Hence, to save the time gauges are used, which can tell whether the part
manufactured is within the prescribed limits or not.
Thus, the need of inspection can be summarized as:
1. To ensure that the part, material or a component conforms to the established standard.
2. To meet the interchangeability of manufacture.
3. To maintain customer relation by ensuring that no faulty product reaches the
customers. Department of Mechanical Engineering
Jaipur Institute of Engineering & Technology, Kukas, Jaipur Page 1.3 1. Introduction Engineering Measurement & Metrology 4. Provide the means of finding out shortcomings in manufacture. The results of inspection
are not only recorded but forwarded to the manufacturing department for taking
necessary steps, so as to produce acceptable parts and reduce scrap.
5. It also helps to purchase good quality of raw materials, tools, equipment which governs
the quality of the finished products.
6. It also helps to co-ordinate the functions of quality control, production, purchasing and
other departments of the organization.
To take decision on the defective parts i.e., to judge the possibility of making some of
these parts acceptable after minor repairs. 1.3 Objectives of Metrology
While the basic objective of a measurement is to provide the required accuracy at
minimum cost, metrology would have further objective in a modern engineering plant
with different shops like Tool Room, Machine Shop, Press Shop, Plastic Shop, Pressure
Die Casting Shop, Electroplating and Painting Shop, and Assembly Shop; as also
Research, Development and Engineering Department. In such an engineering
organization, the further objectives would be as follows:
1. Thorough evaluation of newly developed products, to ensure that components designed
is within the process and measuring instrument capabilities available in the plant.
2. To determine the process capabilities and ensure that these are better than the relevant
3. To determine the measuring instrument capabilities and ensure that these are adequate
for their respective measurements.
4. To minimize the cost of inspection by effective and efficient use of available facilities and
to reduce the cost of rejects and rework through application of Statistical Quality
5. Standardization of measuring methods. This is achieved by laying down inspection
methods for any product right at the time when production technology is prepared.
6. Maintenance of the accuracies of measurement. This is achieved by periodical
calibration of the metrological instruments used in the plant.
7. Arbitration and solution of problems arising on the shop floor regarding methods of
measurement. Page 1.4 Department of Mechanical Engineering
Jaipur Institute of Engineering & Technology, Kukas, Jaipur Engineering Measurement & Metrology 1. Introduction 8. Preparation of designs for all gauges and special inspection fixtures.
Development of Material Standard The need for establishing standard of length was raised primarily for determining
agricultural land areas and for the erection of buildings and monuments. The earliest
standard of length was established in terms of parts of human body. The Egyptian unit
was called a cubit. It was equal to the length of the forearm (from the elbow to the tip of
the middle figure). Rapid advancement made in engineering during nineteenth century was due to
improved materials available and more accurate measuring techniques developed. It
was not until 1855 that first accurate standard was made in England. It was known as
imperial standard yard. This was followed by International Prototype meter made in
France in the year 1872. These two standards of lengths were made of material (metal
alloys) and hence they are called as material standards in contrast to wavelength standard adopted as length standard later on. Imperial Standard Yard The imperial standard yard is made of 1 inch square cross-section bronze bar (82%
copper, 13% tin, 5% zinc) 38 inches long. The bar has two 1/2 inch diameter X 1/2 inch
deep holes. Each hole is fitted with 1/10th inch diameter gold plug. The top surface of
these plugs lie on the neutral axis of the bronze bar.
The purpose of keeping the gold plug lines at neutral axis has the following advantages.
- Due to bending of beam the neutral axis remains unaffected - The plug remains protected from accidental damage.
The top surface of the gold plugs is highly polished and contains three lines engraved
transversely and two lines longitudinally.
The yard is defined as the distance between two central transverse lines on the plugs
when, 1. The temperature of the bar is constant at 62°F and,
2. The bar is supported on rollers in a specified manner to prevent flexure. Department of Mechanical Engineering
Jaipur Institute of Engineering & Technology, Kukas, Jaipur Page 1.5 1. Introduction Engineering Measurement & Metrology Figure 1.1 Imperial Standard Yards
International Standard Meter (Prototype) This standard was established originally by International Bureau of Weights and
Measures in the year 1875. The prototype meter is made of platinum-iridium alloy (90%
platinum and 10% iridium) having a cross-section as shown in Fig. 1.2. The upper surface of the web is highly polished and has two fine lines engraved over it.
It is in-oxidisable and can have a good finish required for ruling good quality of lines. The
bar is kept at 0°C and under normal atmospheric pressure. It is supported by two rollers
of at least one cm diameter symmetrically situated in the same horizontal plane. The
distance between the rollers is kept 589 mm so as to give minimum deflection. The web
section chosen gives maximum rigidity and economy of costly material. The distance
between the centers portions of two lines engraved on the polished surface of this bar
of platinum-iridium alloy is taken as one meter. According to this standard, the length of the meter is defined as the straight line
distance, at 0°C between the centre portions of pure platinum-iridium alloy (90%
platinum, 10% iridium) of 102 cm total length and having a web cross-section as shown
in Fig. 1.2. Page 1.6 Department of Mechanical Engineering
Jaipur Institute of Engineering & Technology, Kukas, Jaipur Engineering Measurement & Metrology 1. Introduction Figure 1.2 International Prototype Meter Cross-sections The metric standard when in use is supported at two points which are 58.9 cm apart as
calculated from Airy's formula, according to which the best distance between the
supporting points is given by Where, L = total length of bar (assumed uniform), b = distance between points, n =
number is supports For prototype meter, This reference was designated as International Prototype Meter M in 1899. It is
preserved by (BIPM) at Sevres in France. The BIPM is controlled by the International
Committee of Weights and Measure. The imperial standard yard was found to be decreasing in length at the rate of onemillionth of an inch for the past 50 years when compared with internal standard meter.
The prototype meter is quite stable. There-fore, yard relationship had to be defined in
terms of meter as 1 yard = 0.9144 meter, or inch = 25.4 mm.
Disadvantages of Material Standard
1. The material standards are influenced by effects of variation of environmental
conditions like temperature, pressure, humidity and ageing etc., and it thus changes in
2. These standards are required to be preserved or stored under security to prevent their
damage or destruction.
3. The replica of these standards was not available for use somewhere else.
Department of Mechanical Engineering
Jaipur Institute of Engineering & Technology, Kukas, Jaipur Page 1.7 1. Introduction Engineering Measurement & Metrology 4. These are not easily reproducible.
5. Conversion factor was to be used for changing over to metric working.
6. Considerable difficulty is experienced while comparing and verifying the sizes of gauges.
Wavelength Standard The major drawback with the metallic standards meter and yard is that their length
changes slightly with time. Secondly, considerable difficulty is experienced while
comparing and verifying the sizes of gauges by using material standards. This may lead
to errors of unacceptable order of magnitude. It therefore became necessary to have a
standard of length which will be accurate and invariable. Jacques Babinet a French
philosopher suggested that wavelength of monochromatic light can be used as natural and invariable unit of length.
In 1907 the International Angstrom (A) unit was defined in terms of wavelength of red
cadmium in dry air at 15°C (6438.4696 A = 1 wavelength of red cadmium). Seventh
General Conference of Weights and Measures approved in 1927, the definition of
standard of length relative to the meter in terms of wavelength of the red cadmium as an alternative to International Prototype meter. Orange radiation of isotope krypton-86 was chosen for new definition of length in 1960,
by the Eleventh General Conference of Weights and Measures. The committee decided
to recommend that Krypton-86 was the most suitable element and that it should be used in a hot-cathode discharge lamp maintained at a temperature of 63° Kelvin.
According to this standard meter was defined as equal to 1650763.73 wavelengths of the red orange radiation of Krypton isotope 86 gases. The standard as now defined can be reproduced to an accuracy of about 1 part in 109.
The meter and yard were redefined in terms of wave length of orange Kr-86 radiation as,
1 meter = 1650763.73 wavelengths, and
1 yard = 0.9144 meter = 0.9144 x 1650763.73 wavelengths
= 1509458.3 wavelengths. Page 1.8 Department of Mechanical Engineering
Jaipur Institute of Engineering & Technology, Kukas, Jaipur Engineering ...
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