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Unformatted text preview: See discussions, stats, and author profiles for this publication at: Engineering Metrology and Measurements (A PRACTICAL GUIDE FOR RELIABLE PRODUCTS) ENGINEERING METROLOGY AND MEASUREMENTS (A PRACTICAL GUIDE FOR RELIABLE PRODUCTS Book · January 2016 CITATIONS READS 0 13,851 Some of the authors of this publication are also working on these related projects: Lean Manufacturing, Lean Sigma, Flexible Manufacturing Systems View project All content following this page was uploaded by Dalgobind Mahto on 21 July 2017. The user has requested enhancement of the downloaded file. Engineering Metrology and Measurements (A PRACTICAL GUIDE FOR RELIABLE PRODUCTS) Dalgobind Mahto (2016) ENGINEERING METROLOGY AND MEASUREMENTS (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 Director 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 of metrology. 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 Course Contents 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 component tolerance. 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 Control Techniques 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 length. 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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