Lecture1 Mme3110 Sem1 1112-1 Introd to Metrology

8/3/2019 Lecture1 Mme3110 Sem1 1112-1 Introd to Metrology

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Lecture 1

Metrology and MeasurementSystems (MME 3110)

Semester1, 2011-2012


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Metrology - Quran perspective

We have created every thing bymeasure (Al-Qamar 54:49)


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Course objectives

The objectives of this course are to:

1. provide an understanding of ISO standardsfor measurement technology.

2. learn the techniques of linear and form

measurements of components used inscience and engineering technology.

3. provide an understanding on theapplication of computers for measurementtechnology.

4. expose the students to measuringtechniques of force, pressure, temperature

and non-destructive testing.


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Course Learning Outcomes

Upon completing this course, the students should be able to:

1) Identify several types of equipment/instrumentsthat are appropriate to specific scientific andengineering applications.

2) Implement ISO standards for measurement

technology for quality control purposes.3) Carry out inspection of work-pieces of various

configurations.

4) Use computer software in measurement techniques

5) Calibrate and apply calibration concept andtechniques on measuring equipment.

6) Apply the basic principles and knowledge ofmeasurement techniques in engineering research.


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Method of Evaluation

Method %

Quizzes 10

Assignment 5 Project 10

Mid-term Exam 25

Final Examination 50


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References

Required:

Galyer, J. F.W. & Shotbolt, C. R. (1990). Metrology for Engineers. PrenticeHall.

Recommended

Busch, T., Harlow, R., & Thompson, R. (1998). Fundamentals of DimensionalMetrology. Delmar Publishers.

Doebelin, E. O. (2004). Measurement Systems-Application and Design.McGrawhill.

Fargo, F. T., & Curtis, M. A. (1994). Handbook of Dimensional Measurement.Industrial Press Inc.

Morris, A. S. (1997). Measurement and Calibration Requirements for QualityAssurance to ISO 9000. John Wiley & Sons.


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Introduction

We measure dimensions and other surfacefeatures of a part to make sure that it ismanufactured consistently and within the

specified range of dimensional accuracy

A manufactured product comprises of partsand they must fit and be assembled

properly so that the product performs itsintended purpose during its service life


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Introduction contd.

Therefore need to learn how parts aremeasured and inspected before they areplaced into assemblies after gaining knowledgeof dimensional accuracies in specific

manufacturing processes Examples of assembly:

- a piston should fit into a cylinder withinspecified tolerances.

- The slideways of a machine tool must beproduced with a certain accuracy so that theparts produced on the machine are, inturn, accurate within specified tolerances


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What is metrology?

It is the science of weights and measures

- Refers primarily to measurements of

length, weight, time, etc.

It also includes other engineeringmeasurements for the establishment of aflat, plane reference surface


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Measurement defined

Measurement - is an act of assigning aspecific value to physical variable

- The physical variable becomes themeasured variable

Measurement - the process of finding the valueof a physical quantity (measurable quantity,

e.g. length, mass, time) experimentally withthe help of special technical means calledmeasuring instruments


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- the value of a physical quantityexpressed as the product of a numerical

value and a unit adapted for thesequantities

Result of a measurement


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How important are measurements?

Measurement is the language of science

It helps us communicate about size, quantity,position, condition etc.

The purpose of measurement is essentially torepresent a property of an object by a numberexpressed in sanctioned units of measurements

Simple measurement error can cost a company a

contract, work, jobs, and lots of money Measurements provide a basis for judgments about:

process information, quality assurance and processcontrol


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Measurable parameters

What do we want to measure?

- Length or distance - mass

- Temperature - Elemental composition

- Viscosity - Displacement or distortions

- Time - Pressure

- Forces - Stress

- Strain - Roughness- Depth - Friction etc


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Statistics and metrology

Fig. shows a relationship betweenthe standard deviation and thearea under the curve. Thesepercentages hold true regardlessof the shape of the normal curve

Normal curve with different standard deviationsbut identical means Normal or Gaussian distribution curve

is such a good description of thevariations that occur in most quality

characteristics in industry that it is thebasis for many techniques.

All normal distributions of variousvariables can be converted tostandardized normal distribution (Fig.above) by using the standardizednormal value, Z.

Standardized Normal or Gaussian distributionwith mean =0 and standard deviation = 1


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Statistics and metrology

Fig. shows three normal curves with the same mean butdifferent standard deviations. The figure illustrates theprinciple that the larger the standard deviation, theflatter the curve (data are widely dispersed), and thesmaller the standard deviation, the more peaked the

curve (data are narrowly dispersed).

Normal curves with different standarddeviations but identical meansStandardized Normal or Gaussian distribution

with mean =0 and standard deviation = 1


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A system - a process which generatesinformation

Examples of a system:- a chemicalreactor, a jet fighter, a gas platform, a

submarine, a car, a human heart, anda weather system

System defined


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System variables Information variables commonly generated

by processes (system) include the following:

Acceleration, Velocity, Displacement, Force-Weight, Pressure, Torque, Volume, Mass,

Flow rate, Level, Density, Viscosity, Ph,Humidity, Temperature, Heat/Light, fluxCurrent, Voltage, Power.

A car (system) generates displacement,

velocity and acceleration variables, and achemical reactor generates temperature,pressure and composition variables.


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Measurement system defined

Measurement system:- includes allcomponents in a chain of hardwareand software that leads from themeasured variable to processed data


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Measurement system purpose Links an observerto a process. Acar driver,

a plant operator for e.g., needs informationthe from process

The purpose of a measurement system isillustrated in the Fig. below:


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Measurement system purpose Measurement systems are important tools for

quantification of the physical variable

Measurement systems can detect andrecognize different degrees of physicalvariables

For scientific and engineering measurement,the selection of equipment, techniques andinterpretation of the measured data areimportant


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General structure of measurement system

A Measurement system may consist ofseveralelements or blocks

However, a generalized Measurement system

consists of:1- Basic functional elements i.e. Sensing,

Signal conditioning, Signal processing and

Data presentation2- Auxiliary functional elements


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Basic / Primary structure of ameasurement system

The Fig. below shows the primary structure of ameasurement system

Sensingelement

Signalconditioningelement

Signalprocessingelement

Datapresentationelement

InputTrue

Value

OutputMeasured

Value

The information variable is ameasured variable.

The input to the measurement system is thetruevalue of the variable; the system output is themeasuredvalueof the variable.


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Basic and auxiliary functional elementsof a measurement system


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Measurement system Elements

Sensing element:- This is in contact withthe process and gives an output which

depends in some way on the variable tobe measured. E.g.

- In thermocouple, the millivolt e. m. f.depends on temperature

- In strain gauge, the resistance dependson mechanical strain


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Signal conditioning element:- This takesthe output of the sensing element andconverts it into a form more suitable for

further processing, usually a d. c. voltage,current or frequency signal. E.g.

- Amplifier amplifies millivolt to volts


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Signal processing element:- Takes theoutput of the conditioning element andconverts it into a form more suitable for

presentation E.g. Analogue-to-digital converter

(ADC) converts a voltage into a digital

form for input to a computer


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Measurement system Elements contd.

Data presentation:- Measured value ispresented in a form which can beeasily recognized by the observer.

- E.g. simple pointer-scale indicator

- Chart recorder

- Visual display unit (VDU)


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Measurement Features

A measurement is always performed withthe help of some measuring instrument

Measurement is impossible withoutmeasuring instruments

Measurement is always an experimentalprocedure


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Some Measurement Terms

Uniformity of measuring instrumentsrefers to the state of instruments inwhich they are all carriers of the

established units

Instrument errors and other

properties are important in order forthem to be used as intended, fallwithin the established limits.


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Measurement Terms contd.

Unity of measurements:- refers to a commonquality of all measurements performed in aregion (in a country, in a group of countries, or

in the world) such that the results ofmeasurements are expressed in terms ofestablished units

The measurement results agree with oneanother within the limits of estimated error oruncertainties


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Measurement Methods

Measurement methods can be classified asfollow:

Direct Measuring: A process by which the

measured value is determined directly, e.g..micrometer, vernier caliper, vernier heightgauge, bevel protractors etc. Such instrumentsare simple and most widely used in production.

Indirect Measuring method: Here thedimension is determined by measuring othervalues functionally related to the requiredvalue, e.g., divider, caliper, sine bar etc.


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Measurement Methods contd.

Comparative: The deviations of themeasured dimensions from a mastergauge are determined, e.g., dialindicators.

Contact method: Measuring tip of theinstrument actually touches the surface tobe measured, e.g., micrometers, calipers,dial indicators etc.

Contactless or non-contact method:No contact is required for measurement,e.g., tool maker's microscope, projectioncomparator etc.


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Measuring instrument types

According to their functions, themeasuring instruments are classified as:

Linear or length measuring instruments

Examples of theses include steel rule,caliper, divider, micrometer, verniercaliper etc.

Angular or angle measuring

instruments: These include combinationset, bevel protractor, sine bar, square,dividing head etc.


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A length may be expressed as thedistance between two lines or as thedistance between two faces.

Thus, the instruments used for thedirect measurement of lineardimensions fall into two categories:-

(i) Line standards

(ii) End standards


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Line Standards: The measurement ismade between two parallel linesengraved across the standard. The

most common example of line standardor line measurement is the 'rule' withits divisions shown as lines marked onit.

End Standards: Measurement is madebetween two flat parallel faces.Examples are slip gauges, end bars,micrometers, vernier calipers etc.


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Measurement instrument and functions


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End

Lecture1 Mme3110 Sem1 1112-1 Introd to Metrology

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