Basic of metrology

Basics of Metrology

1. Basics of Metrology
Lectureby
Mr.C.Ramkumar,
AssistantProfessor/Department
of MechanicalEngineering
KIT-KalaignarKarunanidhi
Institute of Technology

2. Introduction toMetrology
Need
Work piece, Instruments –person –Environment
–Their effect on precision and accuracy
Errors
Errors inMeasurements
Types
Control
Types of standards
BASICS OF METROLOGY

3. •Measurement isaprocessof
comparing inputswithpre-defined
standardandgivingtheoutput.
•Metrology is a science ofmeasurement
•Metrologyisalsoconcernedwiththe
inspectionanditsvariousindustrial
techniques
•For every kind of quantity measured, there must be a unit to
measureit
MEASUREMENTS -Introduction

4. 1.Measurand,aphysicalquantitysuchaslength,weight,andangletobe
measured
2.Reference,tocomparethemeasurand(physicalquantity)witha
knownstandardforevaluation
3.Standard/Reference,thephysicalquantityorpropertytowhich
quantitativecomparisonsaretobemade,whichisinternationally
accepted
STANDARD
(KnownQuantity)
MEASURAND
(UnknownQuantity)
COMPARISON
PROCESS
RESULT
(NumericalValue)
MEASUREMENTS -Introduction

5. Toconvertphysicalparametersintomeaningful
numbers.
Todeterminethetruedimensionsofapart.
Toincreaseourknowledgeandunderstandingofthe
world.
Neededforensuringpublichealthandhumansafety.
Totestiftheelementsthatconstitutethesystem
functionasperthedesign.
Forevaluatingtheperformanceofasystem.
Toensureinterchangeabilitywithaviewtopromoting
massproduction.
Toestablishthevalidityofdesignandforfindingnew
dataandnewdesigns.
NEED FOR MEASUREMENT

6. •IndustrialMetrology-Industrialmetrology’spurposeis
toensurethatinstruments,usedinawidevarietyof
industries,arefunctioningproperly.
•ScientificMetrology-Thisformofmetrologydealswith
theorganizationanddevelopmentofmeasurement
standardsandwiththeirmaintenance.
•LegalMetrology-Concernedwiththemeasurements
thatinfluenceeconomictransactions,legalmetrology
isaveryrefinedtypeofmetrology.
TYPES OF METROLOGY

7. Ageneralizedmeasurementsystemconsistsofthefollowing
components:
1.Primary SensingElement
2.Variable ConversionElement
3.Variable ManipulationElement
4.Data ProcessingElement
5.Data TransmissionSystem
6.Data PresentationElement
COMPONENTS OF GENERALIZED MEASUREMENT SYSTEM

8. GENERALISED MEASURING SYSTEM

9. 1.PrimarySensingElement:
Theprimarysensingelementreceivessignalofthephysical
quantitytobemeasuredasinput.Itconvertsthesignaltoasuitableform
(electrical,mechanicalorotherform),sothatitbecomeseasierforother
elementsofthemeasurementsystem,toeitherconvertormanipulateit.
2.VariableConversionElement:
Variableconversionelementconvertstheoutputoftheprimary
sensingelementtoamoresuitableform.Itisusedonlyifnecessary.
3.VariableManipulationElement:
Variablemanipulationelementmanipulatesandamplifiesthe
outputofthevariableconversionelement.Italsoremovesnoise(ifpresent)
inthesignal.
COMPONENTS OF GENERALIZED MEASUREMENT SYSTEM

10. 4.DataProcessingElement:
Itprocessesthedatasignalreceivedfromthevariablemanipulation
elementandproducessuitableoutput.
5.DataTransmissionSystem:
DataTransmissionSystemissimplyusedfortransmittingdatafrom
oneelementtoanother.Itactsasacommunicationlinkbetween
differentelementsofthemeasurementsystem.
6.DataPresentationElement:
Itisusedtopresentthemeasuredphysicalquantityinahuman
readableformtotheobserver.LEDdisplaysaremostcommonlyused
asdatapresentationelementsinmanymeasurementsystems.
COMPONENTS OF GENERALIZED MEASUREMENT SYSTEM

11. Physical Quantity -
Temperature
Sensing Element -Bulb
ConversionElement
–Pressure
TransmissionElement
ManipulationElement
PresentationElement
ElementConversion
COMPONENTS OF GENERALIZED MEASUREMENT SYSTEM

12. Inmetrology(thescienceofmeasurement),astandardisanobject,or
systemthatbearsadefinedrelationshiptoaunitofmeasurementofa
physicalquantity.
Depending on functions and applications, standards of measurement
are classified asfollows:
(i)InternationalStandards
(ii)Primary Standards
(iii)SecondaryStandards
(iv)WorkingStandards
STANDARDS

13. Defined by Internationalagreement
Periodically evaluated & checked by absolute measurements in terms
of fundamental units ofphysics
representcertainunitsofmeasurementtotheclosestpossible
accuracy attainable by the science and technology ofmeasurement
These standards are not available to ordinary uses like measurement
andcalibrations.
i. International Standardsi

14. Mainfunctionisthecalibrationandverificationofsecondary
standards
ThesearemaintainedattheNationalStandardsLaboratoriesin
differentcountries.ForIndia,itisNationalPhysicalLaboratoryat
NewDelhi.
Theprimarystandardsarenotavailablefortheuseoutsidethe
NationalLaboratory.
Theseprimarystandardsareabsolutestandardsofhighaccuracythat
canbeusedasultimatereferencestandardstocheck,calibrateand
certifythesecondarystandards.
ii. Primary Standards

15. Basicreferencestandardsusedbythemeasurementandcalibration
laboratoriesinindustries
Thesestandardsaremaintainedbytheparticularindustrytowhich
theybelong
Each industry has its own secondarystandard
Eachlaboratoryperiodicallysendsitssecondarystandardtothe
nationalstandardslaboratoryforcalibrationandcomparisonagainst
theprimarystandard
Aftercomparisonandcalibration,theNationalStandardsLaboratory
returnsthesecondarystandardstotheparticularindustriallaboratory
withacertificationofmeasuringaccuracyintermsofprimary
standards
iii. SecondaryStandards

16. main tools of a measuringlaboratory
usedtocheckandcalibratelaboratoryinstrumentforaccuracyand
performance.
Forexample,manufacturingofmechanicalcomponentssuchas
shafts,bearings,gearsetc,useastandardcalledworkingstandardfor
checkingthecomponentdimensions.Example:Pluggaugeisusedfor
checkingtheborediameterofbearings.
iv. WorkingStandards

17. •Physical quantity is expressed inUnits.
•Types:
1.Primary Units –m, Kg,KJ
2.Supplementary Units -rad
3.Derived Units –Kg/KJ
UNITS

18. 1. DirectComparison
2.IndirectComparison
3.ComparativeMethod
4.CoincidenceMethod
5.FundamentalMethod
6. ContactMethod
7.TranspositionMethod
8.ComplementaryMethod
9.DeflectionMethod
10.Contactlessmethod
TYPES OF MEASUREMENTS / METHODS OF
MEASUREMENTS

19. 1. DirectMethod
Measurements aredirectlyobtained
Ex.: Vernier Caliper,Scales.
2. IndirectMethod
Obtained by measuring otherquantities.
Ex: Measurement of strain induced ina
bar due to the appliedforce

20. 3. ComparativeMethod
It’scomparedwithother
value.
known
Ex:Comparators.
4. CoincidenceMethod:
Measurements coincide with certain
lines andsignals.Ex:Comparators.
5. FundamentalMethod:
Measuringaquantitydirectlyinrelatedwiththedefinitionofthat
quantity.

21. 6. TranspositionMethod:
Quantitytobemeasuredisfirst
balancedbyaknownvalueandthen
balancedbyanothernewknownvalue.
Ex:Determinationofmassby
balancingmethods.
7.ComplementaryMethod:
Thevalueofquantitytobemeasuredis
combinedwithknownvalueofthesame
quantity.
Ex:Determinationofthevolumeofa
solid by liquid displacementVolume.
22

22. 1.Deflection and Null typeinstruments
2.Analog and Digitalinstruments
3.Active and passive typeinstruments
4.Automatic and manually operatedinstruments
5.Absolute and secondaryinstruments
6.Contacting and non-contactinginstruments
7.Intelligentinstruments
TYPES OF MEASURINGINSTRUMENTS

23. Theweight
indicatedby
oftheobjectis
thedeflectionor
ofa a
scale.
pointeron
Ex.Spring
movement
graduated
Balance
1. Deflection and Null typeinstruments
Theeffectcausedbythequantitytobe
measuredisnullified.
Forexample,considerthemeasurementof
weightbyanordinarybeambalanceas
showninfig.Theunknownweightplaced
inone-sidecausesthebeamandthe
pointertodeflect.Ex.BeamBalance

24. 2. Analog and DigitalInstruments

25. Inactiveinstruments,thequantitybeing
measuredjustactivatesthemagnitudeof
some,externalpowerinputsource,which
inturnproducesthemeasurement.
Inthistypeofinstruments,another
externalenergyinputsourceispresent
apartfromthequantitytobemeasured.
3. Active and Passive TypeInstruments
Inpassivetypeinstruments,outputis
producedentirelybythequantitybeing
measured.

26. 4. Manual and AutomaticInstruments
Manual instruments require the servicesof a
humanoperator.
When the process of null balance is automated, it
is known termed as automaticinstruments.

27. 5. Absolute and SecondaryInstruments
instrumentsAbsolute
givethevalueofthe
arethosewhich
quantitytobe
measured,intermsoftheconstantsofthe
instrument and their deflectiononly.
SecondaryInstrumentshowsdeflection
directlyintermsofelectricalquantitylike
voltage,current,powerandfrequency.
Theseinstrumentsarecalibratedby
comparisonwithanabsoluteinstrument.

28. 6. Contacting and Non-ContactingInstruments

29. 7. IntelligentInstrument
Microprocessor are incorporated with measuringinstrument

30. ACCURACY VsPRECISION
Measurement is an act of assigning an
accurate and precise value to a physical
variable.
Whatisthedifferencebetween
Precision andAccuracy
Accuracy is ameasureofrightness
Precision is ameasureofexactness
ACCURACY Vs PRECISION

31. Accuracyistheabilityoftheinstrumenttomeasurethe
accurate value(Conformity)
Precisionreferstohowcloselyindividualmeasurements
agreewitheachother(Repeatability)
ACCURACY AND PRECISION

32. 34
FACTORS AFFECTING ACCURACY AND
PRECISION OF A MEASURINGSYSTEM
•A measuring system is made of five basic elements.
Theseare:
1.Standard
2.Workpiece
3.Instrument
4.Person
5.Environment

33. FACTORS AFFECTING ACCURACY OF A MEASURING SYSTEM
1.Standard
Coefficient of thermalexpansion
Stability with time
Elasticproperties
Positionetc
2. Workpiece:
Cleanliness surface finishetc.
Surfacedefects
Hiddengeometry
3.Instrument
Inadequateamplification
Scaleerror
Deformation while handling heavyw/p
Calibrationerror
Readability and Repeatability 35

34. 34
4.Person
Trainingskill
Sense of precisionappreciation
Ability to select measuring instrument &standard
Attitude towards personal accuracyachievement
Planning for measurement technique to have minimum justwith
consistent inprecision
5.Environment
Temperature, pressure andhumidity
Clean surrounding and minimumvibration
Adequateillumination
Temperature equalization between standard w/p &instrument
Higher accuracy can be achieved if all 5 factors are considered,
analysed & steps are taken to eliminatethem
FACTORS AFFECTING ACCURACY OF A MEASURING SYSTEM

35. 35
WhatisErrorinMeasurement?
•MeasurementError(ObservationalError)isthe
differencebetweenameasured(actual)valueandits
truevalue.
•True sizeTheoretical size of a dimension whichis
free fromerrors.
•Actualsizesizeobtainedthroughmeasurement
with permissibleerror.
ERRORS INMEASUREMENT

36. Types of Errors inMeasurements
Gross / BlunderErrors MeasurementErrors
SystematicErrors
Instrumental
Errors
Observational
Errors
Environmental
Errors
Theoretical
Errors
RandomErrors
TYPES OF ERRORS INMEASUREMENT

37. 37
1)GrossorBlunderErrors:
Thiscategoryoferrorsincludesallthehumanmistakeswhile
reading,recordingthereadings.Thebestexampleoftheseerrorsis
apersonoroperatorreadingpressuregauge1.01N/m2as
1.10N/m2
2) MeasurementError:
Themeasurementerroristheresult of thevariation of
a measurement of the truevalue
Usually,Measurementerrorconsistsofarandomerrorand
systematic error.
TYPES OF ERRORS INMEASUREMENT

38. 38
a.SystematicError(ControllableError)
•Asystematicerrorisaconstanterrorthatunderthesame
operatingconditions.
•Systematicerroriscausedbyanyfactorsthatsystematicallyaffect
measurement.
•Classification of systematicerrors:
i.Instrumental Errors –CalibrationError
ii.Environmental Errors –Temp, Pressure,Humidity
iii.Observational Errors -Parallax
iv.Theoretical -Percentage

39. 39
Random Errors (UncontrollableError)
•Random(orindeterminate)errorsarecausedbyuncontrollable
fluctuationsinvariablesthataffectexperimentalresults.
•Randomerrorsarecausedbythesuddenchangeinexperimental
conditionsandnoiseandtirednessintheworkingpersons.These
errorsareeitherpositiveornegative.
•Theseerrorsmaybereducedbytakingtheaverageofalarge
numberofreadings.