- Recent questions and answers in Measurement & Metrology
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Powered by Question2AnswerAnswered: What is precision?
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<h2><strong>Define Precision:</strong></h2><p style="text-align: justify;">The terms precision and accuracy are used in connection with the performance of the instrument. </p><p style="text-align: justify;">Precision is the repeatability of the <a rel="" href="https://mechanicalsite.com/262/what-are-the-methods-of-measurements"><strong>measuring process</strong></a>. It refers to the group of measurements for the same characteristics taken under identical conditions. </p><p style="text-align: justify;">It indicates to what extent the identically performed measurements agree with each other. If the instrument is not precise it will give different (widely varying) results for the same dimension when measured again and again. </p><p style="text-align: justify;">The set of observations will scatter about the mean. </p><p style="text-align: justify;">The scatter of these measurements is designated as 5, the standard deviation. It is used as an index of precision.</p><p style="text-align: justify;">The less the scattering more precise is the instrument. Thus, lower, the value of 5, the more precise is the instrument. </p>
Measurement & Metrologyhttps://mechanicalsite.com/286/what-is-precision?show=287#a287Fri, 15 Mar 2019 13:50:46 +0000Answered: Accuracy of Measurements
https://mechanicalsite.com/284/accuracy-of-measurements?show=285#a285
<h2><strong>Accuracy of Measurements: </strong></h2><p style="text-align: justify;">The purpose of <a rel="" href="https://mechanicalsite.com/276/explain-generalized-measurement-system-and-standards"><strong>measurement</strong></a> is to determine the true dimensions of a part. But no measurement can be made absolutely accurate. There is always some error. The amount of error depends upon the following factors: </p><ol><li>The accuracy and design of the measuring instrument </li><li>The skill of the operator </li><li><a rel="" href="https://mechanicalsite.com/266/what-is-absolute-or-fundamental-measuring-method"><strong>Method adopted for measurement </strong></a></li><li>Temperature variations </li><li>Elastic deformation of the part or instrument etc. </li></ol><p style="text-align: justify;">Thus, the true dimension of the part cannot be determined but can only by approximate. The agreement of the measured value with the true value of the measured quantity is called accuracy.</p><p style="text-align: justify;">If the <a rel="" href="https://mechanicalsite.com/262/what-are-the-methods-of-measurements"><strong>measurement of dimensions</strong></a> of a part approximates very closely to the true value of that dimension, it is said to be accurate. Thus the term accuracy denotes the closeness of the measured value with the true value.</p><p style="text-align: justify;">The difference between the measured value and the true value is the error of measurement. The lesser the error, more is the accuracy. </p>
Measurement & Metrologyhttps://mechanicalsite.com/284/accuracy-of-measurements?show=285#a285Fri, 15 Mar 2019 13:48:31 +0000Answered: Classification of Standards
https://mechanicalsite.com/282/classification-of-standards?show=283#a283
<h2><strong>Classification of Standards: </strong></h2><p style="text-align:justify">To maintain accuracy and <a rel="" href="https://mechanicalsite.com/278/what-is-interchangeability"><strong>interchangeability</strong></a> it is necessary that Standards to be traceable to a single source, usually the <strong>National Standards of the country</strong>, which are further linked to International Standards. The accuracy of National Standards is transferred to working standards through a chain of intermediate standards in a manner given below. </p><ol><li>National Standards </li><li>National Reference Standards </li><li>Working Standards </li><li>Plant Laboratory Reference Standards </li><li>Plant Laboratory Working Standards </li><li>Shop Floor Standards </li></ol><p style="text-align: justify;">Evidently, there is degradation of accuracy in passing from the defining standards to the shop floor standards. The accuracy of particular standard depends on a combination of the number of times it has been compared with a standard in a higher echelon, the frequency of such comparisons, the care with which it was done, and the stability of the particular standards itself. </p>
Measurement & Metrologyhttps://mechanicalsite.com/282/classification-of-standards?show=283#a283Fri, 15 Mar 2019 13:43:19 +0000Answered: What is tolerance?
https://mechanicalsite.com/280/what-is-tolerance?show=281#a281
<h2><strong>About Tolerance:</strong></h2><p><em><strong>Tolerance is equal to algebraic difference between upper and lower deviations and has an absolute value without sign</strong></em>. In the context of this terminology for limits and fits, the difference between maximum limit of size and minimum limit of size is called tolerance. </p><p><u><strong>In the figure given below</strong></u>, tolerance etc. are shown too much exaggerated. It is assured that shaft touches at the bottom of hole and then other dimensions are considered. A line is assumed to be there in between upper tolerance on shaft and lower tolerance on hole. This line is called zero line. </p><p><img alt="Disposition of maximum clearance and minimum clearance. Tolerance." src="https://mechanicalsite.com/?qa=blob&qa_blobid=16624602769770602079" style="height:416.463px; width:773.636px"></p><p>This also refers to basic size from axis of the shaft or hole. All tolerances and deviations are referred to from this datum line. Setting of tolerance value alone is not sufficient to define particular limits, but position of the tolerance zone relative to the basic size of the feature must also be specified. </p>
Measurement & Metrologyhttps://mechanicalsite.com/280/what-is-tolerance?show=281#a281Thu, 14 Mar 2019 14:02:49 +0000Answered: What is interchangeability?
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<h2><strong>About Interchangeability</strong></h2><p style="text-align: justify;">When a system has been worked out, so that any one component will assemble correctly with any mating component , both being chosen at random, the method is called <strong>interchangeable system</strong>.</p><h3><strong>Concept of Interchangeability </strong></h3><p style="text-align: justify;">It is very difficult to <a rel="" href="https://mechanicalsite.com/manufacturing-process"><strong>manufacture</strong></a> any component or part with exact dimensions due to human inaccuracy or machine or process incapability. Thus for the components to meet functional aspect as well as to bring down the <a rel="nofollow" href="https://www.investopedia.com/terms/p/production-cost.asp"><strong>cost of production</strong></a>, principle of interchangeability concept is introduced. Interchangeable production means production of parts to such a degree of accuracy that will ensure an assembly which will meet the functional requirements. </p>
Measurement & Metrologyhttps://mechanicalsite.com/278/what-is-interchangeability?show=279#a279Thu, 14 Mar 2019 13:55:33 +0000Answered: Explain Generalized Measurement System and Standards
https://mechanicalsite.com/276/explain-generalized-measurement-system-and-standards?show=277#a277
<h2><strong>Generalized Measurement System and Standards:</strong></h2><p style="text-align: justify;">The term standard is used to denote universally accepted specifications for devices. Components or processes which ensure conformity and interchangeability throughout a particular industry. A standard provides a reference for assigning a numerical value to a measured quantity. Each basic measurable quantity has associated with it an ultimate standard.</p><p style="text-align: justify;">Working standards, those used in conjunction with the various measurement making instruments. The national institute of standards and technology (NIST) formerly called National Bureau of Standards (NBS), it was established by an act of congress in 1901, and the need for such body had been noted by the founders of the constitution. In order to maintain accuracy, standards in a vast industrial complex must be traceable to a single source, which may be nationals standards.</p><h3><strong>The following is the generalization of echelons of standards in the national <a rel="" href="https://mechanicalsite.com/262/what-are-the-methods-of-measurements">measurement system</a>.</strong></h3><p>1. Calibration standards<br>2. <a rel="" href="https://mechanicalsite.com/248/what-is-metrology"><strong>Metrology standards</strong></a><br>3. National standards</p><h3><strong>1. Calibration standards:</strong></h3><p>Working standards of industrial or governmental laboratories.</p><h3><strong>2. Metrology standards:</strong></h3><p>Reference standards of industrial or Governmental laboratories.</p><h3><strong>3. National standards:</strong></h3><p>It includes prototype and natural phenomenon of Sl (Systems International), the world wide system of weight and measures standards.</p>
Measurement & Metrologyhttps://mechanicalsite.com/276/explain-generalized-measurement-system-and-standards?show=277#a277Wed, 13 Mar 2019 12:48:41 +0000Answered: Explain method of null measurement.
https://mechanicalsite.com/273/explain-method-of-null-measurement?show=275#a275
<h2><strong>Method of null measurement:</strong></h2><p>It is a method of differential measurement. In this method the difference between the value of the quantity to be measured and the known value of the same quantity with which it is compared is brought to zero.</p>
Measurement & Metrologyhttps://mechanicalsite.com/273/explain-method-of-null-measurement?show=275#a275Wed, 13 Mar 2019 12:41:50 +0000Answered: Explain method of measurement by substitution.
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<h2><strong>Method of measurement by substitution:</strong></h2><p>It is a method of direct comparison in which the value of a quantity to be measured is replaced by a known value of the same quantity, so selected that the effects produced in the indicating device by these two values are the same.<br> </p>
Measurement & Metrologyhttps://mechanicalsite.com/272/explain-method-of-measurement-by-substitution?show=274#a274Wed, 13 Mar 2019 12:41:27 +0000Answered: Difference between coincidence, deflection & complementary measurement methods.
https://mechanicalsite.com/270/difference-coincidence-deflection-complementary-measurement?show=271#a271
<h2 style="text-align:justify"><strong>Coincidence method:</strong></h2><p style="text-align:justify">It is a differential <a rel="" href="https://mechanicalsite.com/262/what-are-the-methods-of-measurements"><strong>method of measurement</strong></a> in which a very small difference between the value of the quantity to be measured and the reference is determined by the observation of the coincidence of certain lines or signals. For example, measurement by vernier calliper micrometer.</p><h2 style="text-align:justify"><strong>Deflection method:</strong></h2><p style="text-align:justify">In this method the value of the quantity to be measured is directly indicated by a deflection of a pointer on a calibrated scale.</p><h2 style="text-align:justify"><strong>Complementary method:</strong></h2><p style="text-align:justify">In this method the value of the quantity to be measured is combined with a known value of the same quantity. The combination is so adjusted that the sum of these two values is equal to predetermined comparison value .. For example, determination of the volume of a solid by liquid displacement.</p>
Measurement & Metrologyhttps://mechanicalsite.com/270/difference-coincidence-deflection-complementary-measurement?show=271#a271Wed, 13 Mar 2019 12:38:43 +0000Answered: What are the difference between transposition & Comparative method?
https://mechanicalsite.com/268/what-difference-between-transposition-comparative-method?show=269#a269
<h2><strong>Comparative method:</strong></h2><p>In this method the value of the quantity to be measured is compared with known value of the same quantity or other quantity practically related to it. So, in this method only the deviations from a master gauge are determined, e.g., dial indicators, or other comparators.</p><h2><strong>Transposition method:</strong></h2><p style="text-align: justify;">It is a <a rel="" href="https://mechanicalsite.com/262/what-are-the-methods-of-measurements"><strong>method of measurement</strong></a> by direct comparison in which the value of the quantity measured is first balanced by an initial known value A of the same quantity, then the value of the quantity measured is put in place of this known value and is balanced again by another known value B. If the position of the element indicating equilibrium is the same in both cases, the value of the quantity to be measured is root of AB . For example, determination of a mass by means of a balance and known weights, using the Gauss double weighing</p>
Measurement & Metrologyhttps://mechanicalsite.com/268/what-difference-between-transposition-comparative-method?show=269#a269Wed, 13 Mar 2019 12:35:14 +0000Answered: What is absolute or fundamental measuring method?
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<p style="text-align: justify;">It is based on measurement of the base quantities used to define the quantity. For example, measuring a quantity directly in accordance with the definition of that quantity, or measuring a quantity indirectly by direct measurement of the quantities linked with the definition of the quantity to be measured.</p>
Measurement & Metrologyhttps://mechanicalsite.com/266/what-is-absolute-or-fundamental-measuring-method?show=267#a267Wed, 13 Mar 2019 12:31:48 +0000Answered: Difference between direct method and indirect method of measurements.
https://mechanicalsite.com/264/difference-between-direct-method-indirect-method-measurements?show=265#a265
<h2><strong>1. Direct method of measurement:</strong></h2><p style="text-align: justify;">This is a simple method of <a rel="" href="https://mechanicalsite.com/measurement-metrology"><strong>measurement</strong></a>, in which the value of the quantity to be measured is obtained directly without any calculations. For example, measurements by using scales, vernier callipers, micrometers, bevel protector etc. This method is most widely used in production. This method is not very accurate because it depends on human insensitiveness in making judgment.</p><h2><strong>2. Indirect method of measurement:</strong></h2><p style="text-align: justify;">In indirect method the value of quantity to be measured is obtained by measuring other quantities which are functionally related to the required value. e.g. angle measurement by sine bar, measurement of screw pitch diameter by three wire method etc.</p>
Measurement & Metrologyhttps://mechanicalsite.com/264/difference-between-direct-method-indirect-method-measurements?show=265#a265Wed, 13 Mar 2019 12:28:11 +0000Answered: What are the methods of measurements?
https://mechanicalsite.com/262/what-are-the-methods-of-measurements?show=263#a263
<p>These are the methods of comparison used in <a rel="" href="https://mechanicalsite.com/measurement-metrology"><strong>measurement process</strong></a>. In precision measurement various methods of measurement are adopted depending upon the accuracy required and the amount of permissible error.</p><h2><strong>The methods of measurement can be classified as: </strong></h2><p>1. Direct method</p><p>2. Indirect method</p><p>3. Absolute or Fundamental method</p><p>4. Comparative method</p><p>5. Transposition method</p><p>6. Coincidence method</p><p>7. Deflection method</p><p>8. Complementary method</p><p>9. Contact method</p><p>10. Contact less method</p>
Measurement & Metrologyhttps://mechanicalsite.com/262/what-are-the-methods-of-measurements?show=263#a263Wed, 13 Mar 2019 12:24:08 +0000Answered: What are the necessity and importance of metrology?
https://mechanicalsite.com/260/what-are-the-necessity-and-importance-of-metrology?show=261#a261
<p style="text-align: justify;">The importance of the <a rel="" href="https://mechanicalsite.com/measurement-metrology"><strong>science of measurement</strong></a> as a tool for scientific research (by which accurate and reliable information can be obtained) was emphasized by Galileo and Gvethe. </p><p style="text-align: justify;">This is essential for solving almost all technical problems in the field of engineering in general, and in <a rel="" href="https://mechanicalsite.com/manufacturing-process"><strong>production engineering</strong></a> and experimental design in particular. </p><p style="text-align: justify;">The design engineer should not only check his design from the point of view of strength or economical production, but he should also keep in mind how the dimensions specified can be checked or measured. </p><p style="text-align: justify;">Unfortunately, a considerable amount of engineering work is still being executed without realizing the importance of inspection and quality control for improving the function of product and achieving the economical production. </p><p style="text-align: justify;">Higher productivity and accuracy is called for by the present manufacturing techniques. This cannot be achieved unless the science of <a rel="" href="https://mechanicalsite.com/248/what-is-metrology"><strong>metrology</strong></a> is understood, introduced and applied in industries.</p><p style="text-align: justify;">Improving the quality of production necessitates proportional improvement of the measuring accuracy, and marking out of components before machining and the in-process and post process control of the dimensional and geometrical accuracies of the product.</p><p style="text-align: justify;">Proper gauges should be designed and used for rapid and effective inspection. Also automation and automatic control, which are the modem trends for future developments, are based on measurement. Means for automatic gauging as well as for <a rel="" href="https://mechanicalsite.com/measurement-metrology"><strong>position and displacement measurement</strong></a> with feedback control have to be provided. </p>
Measurement & Metrologyhttps://mechanicalsite.com/260/what-are-the-necessity-and-importance-of-metrology?show=261#a261Wed, 13 Mar 2019 12:14:38 +0000Answered: What are the objectives of metrology?
https://mechanicalsite.com/258/what-are-the-objectives-of-metrology?show=259#a259
<p style="text-align: justify;">Although the basic <strong>objective of a measurement</strong> is to provide the required accuracy at a minimum cost, <a rel="" href="https://mechanicalsite.com/248/what-is-metrology"><strong>metrology</strong></a> has further objectives in a modern engineering plant with different shapes which are: </p><p style="text-align: justify;">1. Complete evaluation of newly developed products.</p><p style="text-align: justify;">2. Determination of the process capabilities and ensure that these are better than the relevant component tolerances. </p><p style="text-align: justify;">3. Determination of the measuring instrument capabilities and ensure that they are quite sufficient for their respective <a rel="" href="https://mechanicalsite.com/measurement-metrology"><strong>measurements</strong></a>.</p><p style="text-align: justify;">4. Minimizing the cost of inspection by effective and efficient use of available facilities.</p><p style="text-align: justify;">5. Reducing the cost of rejects and rework through application of Statistical Quality Control Techniques. </p><p style="text-align: justify;">6. To standardize the measuring methods.</p><p style="text-align: justify;">7. To maintain the accuracies of measurement. </p><p style="text-align: justify;">8. To prepare designs for all gauges and special inspection fixtures. </p>
Measurement & Metrologyhttps://mechanicalsite.com/258/what-are-the-objectives-of-metrology?show=259#a259Wed, 13 Mar 2019 12:09:09 +0000Answered: What are the types of metrology?
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<h2><strong>Basically there are three types of <a rel="" href="https://mechanicalsite.com/248/what-is-metrology">metrology</a>:</strong></h2><ol><li><strong><a rel="" href="https://mechanicalsite.com/250/what-is-legal-metrology">Legal Metrology:</a> </strong>'Legal metrology' is that part of metrology which treats units of measurements, methods of measurements and the measuring instruments, in relation to the technical and legal requirements.</li><li><strong><a rel="" href="https://mechanicalsite.com/254/what-is-deterministic-metrology">Deterministic Metrology:</a> </strong>Deterministic metrology is a new philosophy in which part measurement is replaced by process measurement.</li><li><a rel="" href="https://mechanicalsite.com/252/what-is-dynamics-metrology"><strong>Dynamic Metrology:</strong></a> 'Dynamic metrology' is the technique of measuring small variations of a continuous nature in the field of Measurement & Metrology.</li></ol>
Measurement & Metrologyhttps://mechanicalsite.com/256/what-are-the-types-of-metrology?show=257#a257Tue, 12 Mar 2019 14:26:22 +0000Answered: What is deterministic metrology?
https://mechanicalsite.com/254/what-is-deterministic-metrology?show=255#a255
<p><strong>Deterministic metrology</strong> is a new philosophy in which part measurement is replaced by process measurement.</p><p>The new techniques such as 3D error compensation by <a rel="" href="https://mechanicalsite.com/153/what-are-the-applications-of-cnc-machines"><strong>CNC (Computer Numerical Control)</strong></a> systems and expert systems are applied, leading to fully adaptive control.</p><p>This technology is used for very high precision <a rel="" href="https://mechanicalsite.com/45/what-do-we-study-in-manufacturing-process?show=45#q45"><strong>manufacturing machinery</strong></a> and control systems to achieve micro technology and nanotechnology accuracies. </p>
Measurement & Metrologyhttps://mechanicalsite.com/254/what-is-deterministic-metrology?show=255#a255Tue, 12 Mar 2019 14:17:51 +0000Answered: What is dynamics metrology?
https://mechanicalsite.com/252/what-is-dynamics-metrology?show=253#a253
<p><strong>'Dynamic metrology'</strong> is the technique of measuring small variations of a continuous nature in the field of <a rel="" href="https://mechanicalsite.com/measurement-metrology"><strong>Measurement & Metrology</strong></a>.</p><p>The technique has proved very valuable, and a record of continuous measurement, over a surface, for instance, has obvious advantages over individual measurements of an isolated character. </p>
Measurement & Metrologyhttps://mechanicalsite.com/252/what-is-dynamics-metrology?show=253#a253Tue, 12 Mar 2019 14:13:38 +0000Answered: What is legal metrology?
https://mechanicalsite.com/250/what-is-legal-metrology?show=251#a251
<p><strong>'Legal metrology'</strong> is that part of <a rel="" href="https://mechanicalsite.com/248/what-is-metrology"><strong>metrology</strong></a> which treats units of measurements, <a rel="" href="https://mechanicalsite.com/measurement-metrology"><strong>methods of measurements</strong></a> and the measuring instruments, in relation to the technical and legal requirements.</p><h2><u><strong>The activities of the service of 'Legal Metrology' are:</strong></u></h2><ol><li>Control of measuring instruments;</li><li>Testing of prototypes/models of measuring instruments;</li><li>Examination of a measuring instrument to verify conformity to the statutory requirements etc.</li></ol>
Measurement & Metrologyhttps://mechanicalsite.com/250/what-is-legal-metrology?show=251#a251Tue, 12 Mar 2019 14:11:09 +0000Answered: What is metrology?
https://mechanicalsite.com/248/what-is-metrology?show=249#a249
<p style="text-align: justify;"><strong>Metrology</strong> word is derived from two Greek words such as metro which means measurement and logy which means science. </p><p style="text-align: justify;">Metrology is the science of precision measurement. </p><p style="text-align: justify;">The engineer can say it is the science of measurement of lengths and angles and all related quantities like width, depth, diameter and straightness with high accuracy.</p><p style="text-align: justify;">Metrology demands pure knowledge of certain basic mathematical and physical principles.</p><p style="text-align: justify;">The development of the industry largely depends on the engineering metrology.</p><p style="text-align: justify;">Metrology is concerned with the establishment, reproduction and conservation and transfer of units of measurements and their standards.</p><p style="text-align: justify;">Irrespective of the branch of engineering, all engineers should know about various instruments and techniques. </p><h2><u><strong>Definition of Metrology:</strong></u></h2><p style="text-align: justify;">Measurement is defined as the process of numerical evaluation of a dimension or the process of comparison with standard measuring instruments. The elements of measuring system include the instrumentation, calibration standards, environmental influence, human operator limitations and features of the work-piece. The basic aim of measurement in industries is to check whether a component has been manufactured to the requirement of a specification or not. </p>
Measurement & Metrologyhttps://mechanicalsite.com/248/what-is-metrology?show=249#a249Tue, 12 Mar 2019 14:02:31 +0000