Measurement System

Introduction to electrical and electronic measurement system where basics on measurement, units, static and dynamic characteristics of instruments, order of instruments, are discussed in brief. Errors in instrumentation system is discussed. Calibration and traceability of instruments are illustrated.

1. Electrical & Electronic Measurement
Part –I
Measurement System
ER. FARUK BIN POYEN
[email protected]
AEIE, UIT, BU

2. Contents:
Introduction
Order of Instruments
Instruments Classification
Units of Measurement
Standards of Measurement
Dimensions of Measurement
Errors in Measurement
Instrument Characteristics
Calibration of Instruments
References
2

3. Introduction: 1… of 5
Instrumentationisthatbranchofengineeringthatprimarilydealswithsensing,
measurementandcontrol.
Electricalandelectronicinstrumentationdealswiththeelectricalandelectronic
instrumentswhichareusedformeasurement.
Itisstudyofoperationandfunctionalityofinstruments.
Instrumentationisatechnologyformeasurement.
Useofmeasuringinstrumentsdependsupontheparticularapplication.
Aninstrumentisdefinedasthedeviceorthesystemwhichisdesignedinsuchaway
thatitmaintainsthefunctionalrelationshipbetweenaprescribedpropertyofa
substanceandaphysicalvariable,andcommunicatesthisrelationshiptoahuman
observerbysomewaysandmeans.
3

4. Introduction: 2… of 5
Measurementismadeforthefollowingpurpose:
1.Tomonitorprocessandoperation.
2.Tocontrolprocessandoperation.
3.Tocarryoutsomeanalysis.
Monitoring:Allinstrumentsindicateaparticularquantity.Thesearecalledreadingsof
particularsystem.Innormalsense,readingsdonotperformcontrolling.Itismadefor
monitoringpurpose.
Controlling:Incaseafterreading,ifwewanttochangethevalueofoutputthenwe
controlourinstruments.Forexamplewhenonemeasuresbodytemperature(fever)and
itisnotnormalthenwecontrolthisparticulartemperatureandwanttogetitnormal
applyingmedication.
Analysis:Predictionandoriginalvalueofoutputcomesintoanalysis.
4

5. Introduction: 3… of 5
Characteristics of instruments can be divided into two types:
Desirable
1.Accuracy
2.Sensitivity
3.Reproducibility
Undesirable
1.Drift
2.Dead zone -Hysteresis
i. Threshold
ii. Resolution
3.Static error
5

6. Introduction: 4… of 5
Fortheresulttobemeaningful,therearetwobasicrequirements:
1.Thecomparisonstandardisaccuratelydefinedandcommonlyaccepted.
2.Theprocedureandtheinstrumentusedforobtainingthecomparisonmustbeprovable.
Anelectronicinstrumentisonewhichisbasedonelectronicorelectricalprinciplesforits
measurementfunction.
Themeasurementofanyelectronicorelectricalquantityorvariableistermedasan
electronicmeasurementprovideditgivesdigitizedoutput.
6

7. Introduction: 5… of 5
FavorableconditionsforElectronicMeasurementare:
1.Mostofthequantitiescanbetransducedintotheelectricalorelectronicsignals.
2.Anelectronicorelectricalsignalcanbeamplified,filtered,multiplexed,sampledand
measured.
3.Themeasurementcaneasilybeobtainedandconvertedintosomedigitalformfor
automaticanalysisandrecording.
4.Themeasuredsignalscanbetransmittedoverlongdistanceswiththehelpofcable,radio
links,wirelesscommunicationetc.
5.Manymeasurementscanbecarriedeithersimultaneouslyorsuccessively.
6.Electroniccircuitscandetectandamplifyveryweaksignalsandcanmeasuretheeventsof
veryshortdurationaswell.
7.Electronicmeasurementcanbuildanaloganddigitalsignals.
8.Highersensitivity,lowpowerconsumptionandhigherdegreeofreliabilityarethe
importantfeaturesofelectronicinstrumentsandmeasurements.
7

8. Order of Instruments: 1 … of 3
OrderofaSystem:Theorderofthesystemisdefinedbythenumberofindependent
energystorageelementspresentinthesystem,andintuitivelybythehighestorderof
thelineardifferentialequationthatdescribesthesystem.Inatransferfunction
representation,theorderisthehighestexponentinthetransferfunction.
ZeroOrder:Thisistheresponseoftendesiredininstrumentsbecauseitmeansthat
theblockdoesnotalterthetimeresponse.Allinstrumentsbehaveaszeroorder
instrumentswhentheygiveastaticoutputinresponsetoastaticinput.
Example:WireStrainGauge.
8

9. Order of Instruments: 2… of 3
FirstOrder:Thesystemwhoseinput-outputequationisafirstorderdifferential
equationiscalledafirstordersystem.Theorderofthedifferentialequationisthe
highestdegreeofderivativepresentinanequation.Firstordersystemcontainsonly
oneenergystoringelement.
Example:Mass-DamperSystem;MassHeatingSystem.
SecondOrder:Asystemwhoseinput-outputequationisasecondorderdifferential
equationiscalledaSecondOrderSystem.Thereareanumberoffactorsthatmake
secondordersystemsimportant.Theyaresimpleandexhibitoscillationsand
overshoot.
Example:Mass-Spring-DamperSystemsandRLCCircuits.
9

10. Order of Instruments: 3… of 3
Zero Order
First Order
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Second Order
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11. Electrical Parameter Measuring Reference11

12. Instruments Classification: 1 … of 7 12
Theinstrumentusedformeasuringthephysicalandelectricalquantitiesisknownas
themeasuringinstrument.
Thetermmeasurementmeansthecomparisonbetweenthetwoquantitiesofthesame
unit.
Themagnitudeofoneofthequantityisunknown,anditiscomparedwiththe
predefinedvalue.
Theresultofthecomparisonisobtainedinnumericalvalue.
Themeasuringinstrumentcategorisedintothreetypes;
1.ElectricalInstrument
2.ElectronicInstrument
3.MechanicalInstrument

13. Instruments Classification: 2… of 7 13

14. Instruments Classification: 3… of 7 14
Themechanicalinstrumentisusedformeasuringthephysicalquantities.This
instrumentissuitableformeasuringthestaticandstableconditionsbecausethe
instrumentisunabletogivetheresponsetothedynamiccondition.
Theelectronicinstrumenthasquickresponsetime.Theinstrumentprovidesaquick
responseascomparedtotheelectricalandmechanicalinstrument.
Theelectricalinstrumentisusedformeasuringelectricalquantitieslikecurrent,
voltage,power,etc.,viz.ammeter,voltmeter,wattmeter.

15. Instruments Classification: 4… of 7 15
AbsoluteInstrumentgivesthevalueofmeasuredquantitiesregardingthephysical
constant.Thephysicalconstantmeanstheangleofdeflection,degreeandmeterconstant.
Mathematicalcalculationsarerequiredforknowingthevalueofaphysicalconstant.
Thetangentgalvanometerisanexampleoftheabsoluteinstruments.Intangent
galvanometer,themagnitudeofcurrentpassingthroughthecoilisdeterminedbythe
tangentoftheangleofdeflectionofitscoil,thehorizontalcomponentoftheearth
magneticfield,radiusandthenumberofturnsofwireused.
SecondaryInstrument:Thedeflectionshowsthemagnitudeofthemeasurable
quantities.Thecalibrationoftheseinstrumentswiththestandardinstrumentisessential
forthemeasurement.Theoutputofthistypeofdeviceisdirectlyobtained,andno
mathematicalcalculationisrequiredforknowingtheirvalue.

16. Instruments Classification: 5… of 7 16
DigitalInstrumentgivestheoutputinthenumericform.Theinstrumentismore
accurateascomparedtotheanalogueinstrumentbecausenohumanerroroccursinthe
reading.
Analogueinstrumentistheinstrumentwhoseoutputvariescontinuously.Theanalogue
instrumenthasthepointerwhichshowsthemagnitudeofthemeasurablequantities.
Theanaloguedeviceisfurtherclassifiedintotwotypes.
1.NullType
2.DeflectionType

17. Instruments Classification: 6… of 7 17
NullTypeInstrument
Inthisinstrument,thezeroornulldeflectionindicatesthemagnitudeofthemeasured
quantity.Theinstrumenthashighaccuracyandsensitivity.Innulldeflection
instrument,oneknownandoneunknownquantityareused.Whenthevalueofthe
knownandtheunknownmeasuringquantitiesareequal,thepointershowsthezeroor
nulldeflection.Thenulldeflectioninstrumentisusedinthepotentiometerandin
galvanometerforobtainingthenullpoint.
DeflectionTypeInstrument
Theinstrumentinwhichthevalueofmeasuringquantityisdeterminedthroughthe
deflectionofthepointerisknownasthedeflectiontypeinstrument.Themeasuring
quantitydeflectsthepointerofthemovingsystemoftheinstrumentwhichisfixedon
thecalibratedscale.Thus,themagnitudeofthemeasuredquantityisknown.

18. Instruments Classification: 7… of 7 18
Thedeflectiontypeinstrumentisfurthersub-classifiedintothreetypes.
1.IndicatingInstrument–Theinstrumentwhichindicatesthemagnitudeofthemeasured
quantityisknownastheindicatinginstrument.Theindicatinginstrumenthasthedial
whichmovesonthegraduatedscale.E.g.,voltmeter,ammeter,powerfactormeter.
2.IntegratingInstrument–Theinstrumentwhichmeasuresthetotalenergysuppliedata
particularintervaloftimeisknownastheintegratinginstrument.Thetotalenergy
measuredbytheinstrumentistheproductofthetimeandthemeasuredelectrical
quantities.E.g.,energymeter,watt-hourmeter.
3.RecordingInstrument–Theinstrumentthatrecordsthecircuitconditionataparticular
intervaloftimeisknownastherecordinginstrument.Themovingsystemofthe
recordinginstrumentcarriesapenwhichlightlytouchesonthepapersheet.The
movementofthecoilistracedonthepapersheet.Thecurvedrawnonthepapershows
thevariationinthemeasurementoftheelectricalquantities.

19. Units of Measurement:
Metrologyisthescienceofdevelopingnationallyandinternationallyacceptedunitsof
measurement.
Aunitisanystandardusedformakingcomparisonsinmeasurements.
Unitconversionsallowformeasurementsofapropertythathavebeenrecordedusingdifferent
units
Themetricsystemisaframeworkofunitsofmeasurementthathasgrownfromits1874birth
inadiplomatictreatytothemoremodernGeneralConferenceonWeightsandMeasures,or
CGPM(ConferérenceGénéraledesPoidsetMeasures).
ThemodernsystemisproperlycalledtheInternationalSystemofUnits,orSI,anabbreviation
fromtheFrenchLeSystèmeInternationald'Unités.
Today,mostpeopleusethenamesmetricandSIinterchangeably.
Themetricsystemisthemainsystemofmeasurementunitsusedinscience.
Eachunitisconsideredtobedimensionallyindependentoftheothers.
Thesedimensionsaremeasurementsoflength,mass,time,electriccurrent,temperature,
amountofasubstance,andluminousintensity.
19

20. Units of Measurement: 7 Base Metric Units
Length:Meter(m)Themeteristhemetricunitoflength.Itisdefinedasthelengthof
thepathlighttravelsinavacuumduring1/299,792,458
th
ofasecond.
Mass:Kilogram(kg)Thekilogramisthemetricunitofmass.Itisthemassofthe
internationalprototypeofthekilogram:astandardplatinum/iridium1kgmasshoused
nearParisattheInternationalBureauofWeightsandMeasures(BIPM).
Time:Second(s)Thebasicunitoftimeisthesecond.Thesecondisdefinedasthe
durationof9,192,631,770oscillationsofradiationcorrespondingtothetransition
betweenthetwohyperfinelevelsofcesium-133.
Temperature:Kelvin(K)TheKelvinistheunitofthermodynamictemperature.Itisthe
fraction1/273.16ofthethermodynamictemperatureofthetriplepointofwater.The
Kelvinscaleisanabsolutescale,sothereisnodegree.
Thetriplepointisthetemperatureandpressureatwhichsolid,liquid,andvapour
phasesofaparticularsubstancecoexistinequilibrium.
20

21. Units of Measurement: 7 Base Metric Units
AmountofaSubstance:Mole(mol)Themoleisdefinedastheamountofasubstance
thatcontainsasmanyentitiesasthereareatomsin0.012kilogramsofcarbon-12.
Whenthemoleunitisused,theentitiesmustbespecified.Forexample,theentities
maybeatoms,molecules,ions,electrons,cows,houses,oranythingelse.
LuminousIntensity:Candela(cd)Theunitofluminousintensity,orlight,isthe
Candela.Thecandelaistheluminousintensity,inagivendirection,ofasource
emittingmonochromaticradiationoffrequency540x1012hertzwithradiantintensity
inthatdirectionof1/683wattpersteradian.
ElectricCurrent:Ampere(A)Thebasicunitofelectriccurrentistheampere.The
ampereisdefinedastheconstantcurrentthat,ifmaintainedintwoinfinitelylong
straightparallelconductorswithanegligiblecircularcross-sectionandplaced1m
apartinavacuum,wouldproduceaforcebetweentheconductorsequalto2x10-7
Newtonpermeteroflength.
21

22. Units of Measurement: Other Basic Units
Liter(L)Whilethemetricunitofvolumeisthecubicmeter,??????
3
,themostcommonly
usedunitistheliter.Aliterisequalinvolumetoonecubicdecimeter,??????
3
,whichisa
cubethatis0.1moneachside.
Angstrom(Å)Oneangstromequals10
−8
cmor10
−10
m.NamedafterAndersJonas
Ångstrom,theunitisusedtomeasurethechemicalbondlengthandelectromagnetic
radiationwavelength.
Cubiccentimeter(????????????
3
)Acubiccentimeterisacommonunitusedtomeasuresolid
volume.Thecorrespondingunitforliquidvolumeisthemilliliter(mL),whichisequalto
onecubiccentimeter.
22

23. Units of Measurement: Derived Units
Thesevenbaseunitsformthebasisforderivedunits.Stillmoreunitsareformedby
combiningbaseandderivedunits.
1.Radian (rad): Unit used to quantify an angle.??????.??????
−1
2.Hertz (Hz): Used for frequency.s
−1
3.Newton (N): Unit of weight or force.kg⋅m⋅s
−2
4.Joule (J): Unit of energy, heat, or work.kg⋅m
2
⋅s
−2
5.Watt (W): Unit of power or radiant flux.kg⋅m
2
⋅s
−3
6.Coulomb (C): Unit of electric charge.�.??????
7.Volt (V): Unit of electric potential or voltage.kg⋅m
2
⋅s
−3
⋅A
−1
8.Farad (F): Unit of capacitance.kg
−1
⋅m
−2
⋅s
4
⋅A
2
9.Tesla (T): Metric unit of magnetic flux density.kg⋅s
−2
⋅A
−1
10.Degree Celsius (°C): Temperature relative to 273.15 K.
11.Gray(Gy): Unit of absorbed radiation dose.m
2
⋅s
−2
23

24. Units of Measurement: Systems of Units
Asystemofunitsisasetofrelatedunitsthatareusedforcalculations.Thesystem
includesbaseunits,whichrepresentbasedimensions,andderivedunits,which
representproductsofpowersofbasedimensions.
1.SI(InternationalSystemofUnits)(meter-kilogram-second-ampere-kelvin-mole-
candela)
2.FPS(foot-pound-second)
3.MKS(meter-kilogram-second)
4.CGS(centimeter-gram-second)
5.EMU(Electromagnetic)(centimeter-gram-second-abampere)
6.ESU(Electrostatic)(centimeter-gram-second-abcoulomb)
7.Atomic(bohr-electronmass-atomicsecond-electron)
8.MTS(meter-tonne-second)
24

25. Standards of Measurement:
Inmetrology(thescienceofmeasurement),astandard(oretalon)isanobject,system,
orexperimentthatbearsadefinedrelationshiptoaunitofmeasurementofaphysical
quantity.
Standardsarethefundamentalreferenceforasystemofweightsandmeasures,against
whichallothermeasuringdevicesarecompared.
Thereisathree-levelhierarchyofphysicalmeasurementstandards.
1.PrimaryStandardsmadetothehighestmetrologicalqualityandarethedefinitive
definitionorrealizationoftheirunitofmeasure.
2.SecondaryStandardsareverycloseapproximationsofprimaryreferencestandards
whicharecalibratedagainsttheprimarystandards.
3.WorkingStandardsareusedforcheckingitsmeasuringinstrumentsusedinindustries
havingatraceablerelationshiptothesecondaryandprimarystandardsandthey
deteriorateovertime.
25

26. Dimensions of Measurement:
Dimensionsofaphysicalquantityarethepowerstowhichthefundamentalquantities
mustberaisedtorepresentthegivenphysicalquantity.
Inmechanics,allphysicalquantitiescanbeexpressedintermsofmass(M),length(L)
andtime(T).
Dimensionalmeasurementishowweknowandquantifythesizeandshapeofthings.
Itinvolveslengthsandanglesaswellasgeometricalpropertiessuchasflatnessand
straightness.
Dimensionalmeasurementisoffundamentalimportanceforinterchangeabilityand
globaltrade.Itishowweensurethatthingswillfittogether.
Withoutgloballengthstandardsasthebasisforstandardizedpartsglobalizedindustry
wouldnotbepossible.
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27. Errors in Measurement:
Themeasurementerrorisdefinedasthedifferencebetweenthetrueoractualvalue
andthemeasuredvalue.
Thetruevalueistheaverageoftheinfinitenumberofmeasurements,andthe
measuredvalueistheprecisevalue.
27

28. Errors in Measurement –Types 1… of 4
Thegrosserrorwhichoccursbecauseofthehumanmistakes.Itcanonlybeavoidedby
takingthereadingcarefully.
SystematicErrors
1.InstrumentalErrors(inherent,Misuse,Loading)
2.EnvironmentalErrors
3.ObservationalErrors
RandomErrorswhicharecausedbythesuddenchangeintheatmosphericcondition,
arecalledrandomerror.Thesetypesoferrorremainevenaftertheremovalofthe
systematicerror.Hencethistypeoferrorisalsocalledresidualerror.
28

29. Errors in Measurement –Types 2... of 4
InstrumentalErrorarisesduetothreemainreasons:
1.InherentShortcomingsofInstruments–Suchtypesoferrorsareinbuiltininstruments
becauseoftheirmechanicalstructure.
2.MisuseofInstrument–Theerroroccursintheinstrumentbecauseofthefaultofthe
operator.Agoodinstrumentusedinanunintelligentwaymaygiveanenormous
result.
3.LoadingEffect–Itisthemostcommontypeoferrorwhichiscausedbythe
instrumentwhilemeasuring.Forexample,whenthevoltmeterisconnectedtothe
highresistancecircuititgivesamisleadingreading,andwhenitisconnectedtothe
lowresistancecircuit,itgivesthedependablereading.Thismeansthatthevoltmeter
hasaloadingeffectonthecircuit.
29

30. Errors in Measurement –Types 3… of 4
EnvironmentalErrors
Theseerrorsareduetotheexternalconditionofthemeasuringdevices.Suchtypesof
errorsmainlyoccurduetotheeffectoftemperature,pressure,humidity,dust,vibration
orbecauseofthemagneticorelectrostaticfield.Thecorrectivemeasuresemployedto
eliminateortoreducetheseundesirableeffectsare
1.Thearrangementshouldbemadetokeeptheconditionsasconstantaspossible.
2.Usingtheequipmentwhichisfreefromtheseeffects.
3.Byusingthetechniqueswhicheliminatetheeffectofthesedisturbances.
4.Byapplyingthecomputedcorrections.
ObservationalErrors
Suchtypesoferrorsareduetothewrongobservationofthereading.Therearemany
sourcesofobservationalerror.Forexample,thepointerofavoltmeterresetsslightly
abovethesurfaceofthescale.Thusanerroroccurs(becauseofparallax)unlesstheline
ofvisionoftheobserverisexactlyabovethepointer.Tominimisetheparallaxerror
highlyaccuratemetersareprovidedwithmirroredscales.
30

31. Errors in Measurement –Types 4… of 4 31

32. Instrument Characteristics:
InstrumentCharacteristicsallowuserstoselectthemostsuitableinstrumentfor
specificmeasuringjobs.
Therearetwobasicperformancecharacteristicsofmeasuringinstrument:
1.StaticCharacteristics:valueofthemeasuredvariablechangeslowly.
2.DynamicCharacteristics:valueofthemeasuredvariablechangeveryfast.
Thestaticcharacteristicsandparametersofmeasuringinstrumentsdescribethe
performanceoftheinstrumentsrelatedtothesteady-stateinput/outputvariablesonly.
Thevariousstaticcharacteristicsandparametersaredestinedforquantitative
descriptionoftheinstrument.
Dynamiccharacteristicshowsthetimeresponsebehavioroftheinstrumenttothe
changesinthemagnitudeofinterestbyobservingthesignaloutputwithtime.
32

33. Static Characteristics:
1.Accuracy:Closenessofameasurementtothetruevalue.
2.Precision:Closenessofagreementamongasetofresults.
3.Sensitivity:Incrementoftheoutputsignal(orresponse)totheincrementoftheinput
measuredsignal.
4.Repeatability:Variationinmeasurementstakenonthesameitemunderthesame
conditions.
5.Reproducibility:Abilityofameasurementtobeduplicated,eitherbythesameperson
orbysomeoneelseunderchangedconditions.
6.Drift:Changeininstrumentoutputovertime-whenthetruevalueisconstant.
7.Resolution:Minimumchangeininputthatisrequiredforchangeinoutput.
8.Threshold:Theminimumlimitoftheinputreading.
33

34. Static Characteristics:
9.Range:Inputrangeofameasuringdevicespecifiedbytheminimumandmaximum
valuesofinputvariable.
10.Span:Differencebetweenthemaximumandtheminimumvaluesofinputvariables.
11.Linearity:Maximumdeviationfromlinearrelationbetweeninputandoutput.
12.Error:Deviationofthetruevaluefromthedesiredvalue.
13.Hysteresis:Whenunloadingappliedinputdonotcreatethesameoutput.
14.Creep:Timeaninstrumentneedstoadapttochangeinappliedinput.
15.Trueness:Closenessofthemeanofasetofmeasurementresultstotheactual(true)
value.
16.Calibration:
34

35. Dynamic Characteristics:
Speedofresponse
DynamicError:Thedifferencebetweenthetrueandmeasuredvaluewithnostatic
error.
Lag:Responsedelay
Fidelity:Thedegreetowhichaninstrumentindicatesthechangesinthemeasured
variablewithoutdynamicerror(faithfulreproduction).
35

36. Calibration & Traceability of Instruments:
Calibrationisacomparisonbetweenaknownmeasurement(thestandard)andthe
measurementcarriedoutusinganotherinstrument.
Calibrationisthewaythatthestandardsaretransferredfromonecountrytoanother,andfrom
oneinstrumenttoanother.
TheprimaryreferencestandardsfortheSIunitsofmeasurementareheldinFranceandeach
countrycomparestheirnationalstandardsagainstthese.
Calibrationofmeasuringinstrumentshasthreeobjectives.
1.Checkingfortheaccuracyoftheinstrument.
2.Determiningthetraceabilityofthemeasurement.
3.Repairingofthedeviceifitisoutofcalibration.
Measurementtraceabilityisusedtorefertoanunbrokenchainofcomparisonsrelatingan
instrument'smeasurementstoaknownstandard.
Traceabilityofinstrumentsisusedtodetermineitsbias,accuracyandprecision.
Atraceablemeasurementisonewhichhasanunbrokenchainofcalibrationsgoingbacktothe
primaryreferencestandard,withuncertaintiescalculatedforeachcalibration.
36

37. References:
https://www.livewebtutors.com/assignment-help/electrical-engineering/electrical-and-
electronic-instrumentation
https://circuitglobe.com/classification-of-measuring-instruments.html
https://circuitglobe.com/measurement-error.html
https://www.thoughtco.com/metric-units-base-units-604140
https://www.maplesoft.com/support/help/Maple/view.aspx?path=Units%2FSystems
https://www.muelaner.com/dimensional-measurement/
https://www.muelaner.com/metrology/
https://www.muelaner.com/metrology/#calibration
https://www.engineeringtoolbox.com/instruments-static-characteristics-d_1985.html
http://ecoursesonline.iasri.res.in/mod/resource/view.php?id=3311
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