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Industrial

Process

Sensors

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IndustrialProcess

Sensors

David M. ScottDupont Company

Experimental Station

Wilmington, Delaware, U.S.A.

CRC Press is an imprint of the

Taylor & Francis Group, an informa business

Boca Raton London New York

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CRC PressTaylor & Francis Group6000 Broken Sound Parkway NW, Suite 300Boca Raton, FL 33487-2742

2008 by Taylor & Francis Group, LLCCRC Press is an imprint of Taylor & Francis Group, an Informa business

No claim to original U.S. Government worksPrinted in the United States of America on acid-free paper10 9 8 7 6 5 4 3 2 1

International Standard Book Number-13: 978-1-4200-4416-4 (Hardcover)

is book contains information obtained from authentic and highly regarded sources. Reprintedmaterial is quoted with permission, and sources are indicated. A wide variety of references arelisted. Reasonable efforts have been made to publish reliable data and information, but the authorand the publisher cannot assume responsibility for the validity of all materials or for the conse-quences of their use.

No part of this book may be reprinted, reproduced, transmitted, or utilized in any form by anyelectronic, mechanical, or other means, now known or hereafter invented, including photocopying,microfilming, and recording, or in any information storage or retrieval system, without writtenpermission from the publishers.

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Trademark Notice: Product or corporate names may be trademarks or registered trademarks, andare used only for identification and explanation without intent to infringe.

Library of Congress Cataloging-in-Publication Data

Scott, David M.Industrial process sensors / David M. Scott.

p. cm.Includes bibliographical references and index.ISBN 978-1-4200-4416-4 (alk. paper)1. Engineering instruments. 2. Detectors. I. Title.

TA165.S38 2007670.427--dc22 2007034223

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Dedication

To

L. A. Lundgrenteacher, mentor, and friend

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ii

Contents

Preace...........................................................................................................................xi

Acknowledgments..................................................................................................... xiii

AbouttheAuthor................................................................................................................... xv

1Introduction1.1 MotivationorProcessMeasurement................................................................1

1.2 ProcessSensors......................................................................................................2

1.3 TePhysicsoMeasurement................................................................................4

2 Measurement2.1 TeSensorModel..................................................................................................7

2.2 UnitsoMeasure....................................................................................................8

2.3 SimpleStatistics.....................................................................................................9

2.4 SourcesoError...................................................................................................11

2.5 AnalysisoError..................................................................................................13

3 SoundandWavePhenomena3.1 Sound.....................................................................................................................17

3.2 Waves.....................................................................................................................19

3.3 TeWaveEquationandItsSolutions...............................................................21

3.4 WavePhenomena................................................................................................ 23

3.4.1 Reection............................................................................................... 23

3.4.2 Reraction............................................................................................... 23

3.4.3 SuperpositionandIntererence.......................................................... 25

3.4.4 Resonance.............................................................................................. 27

3.4.5 DopplerShi.......................................................................................... 27

3.4.6 Diraction.............................................................................................. 29

3.5 SoundGenerationandDetection.................................................................... 30

3.6 AppendixontheWaveEquation......................................................................31

4 Light4.1 ElectromagneticWaves.......................................................................................35

4.2 OpticalElements................................................................................................. 38

4.2.1 Mirrors................................................................................................... 38

4.2.2 PrismsandGratings..............................................................................39

4.2.3 BeamSplitters.........................................................................................39

4.2.4 Lenses...................................................................................................... 40

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4.2.5 Apertures.................................................................................................41

4.2.6 Filters.......................................................................................................41

4.2.7 Modulators............................................................................................. 42

4.3 LightGenerationandDetection...................................................................... 444.3.1 IncoherentSources............................................................................... 44

4.3.2 Lasers...................................................................................................... 45

4.3.3 Detectors................................................................................................ 46

5 ElectricityandElectronicDevices5.1 Electricity............................................................................................................. 49

5.1.1 PotentialandCurrent.......................................................................... 49

5.1.2 Resistance............................................................................................... 54

5.1.3 CapacitanceandInductance................................................................555.2 SemiconductorDevices..................................................................................... 58

5.2.1 Diodes..................................................................................................... 58

5.2.2 ransistors...............................................................................................59

5.2.3 IntegratedCircuits................................................................................ 60

5.3 Amplifers............................................................................................................ 60

5.4 Digitization.......................................................................................................... 63

6 IonizingRadiation6.1 Introduction........................................................................................................ 67

6.2 ypesoIonizingRadiation.............................................................................. 69

6.2.1 EnergeticElectromagneticWaves...................................................... 69

6.2.2 EnergeticParticles.................................................................................70

6.3 Sources...................................................................................................................71

6.3.1 NuclearDecay........................................................................................71

6.3.2 X-RayGenerators.................................................................................. 72

6.3.3 CosmicRays........................................................................................... 73

6.4 Detectors.............................................................................................................. 73

6.4.1 Counters................................................................................................. 736.4.2 ImagingDevices....................................................................................74

6.5 SaetyConsiderations........................................................................................ 77

7 ConventionalSensors7.1 Introduction........................................................................................................ 79

7.2 emperatureSensors.......................................................................................... 79

7.2.1 Termistors............................................................................................ 80

7.2.2 Termocouples...................................................................................... 82

7.2.3 InraredTermometers....................................................................... 83

7.3 PressureSensors.................................................................................................. 85

7.3.1 Diaphragms........................................................................................... 85

7.3.2 CapacitanceManometers.................................................................... 87

7.3.3 StrainGauges......................................................................................... 87

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7.4 LevelSensors....................................................................................................... 87

7.4.1 CapacitiveSensors................................................................................ 88

7.4.2 UltrasonicandAcousticSensors........................................................ 88

7.4.3 Radarime-DomainReectometers................................................. 897.5 FlowRateSensors............................................................................................... 89

7.5.1 HeatranserSensors.......................................................................... 89

7.5.2 UltrasonicSensors................................................................................ 90

7.5.3 ElectromagneticSensors...................................................................... 93

7.5.4 DierentialPressureSensors.............................................................. 94

8 ParticleSize8.1 Introduction........................................................................................................ 97

8.1.1 RepresentationoParticleSize........................................................... 978.1.2 ypesoPSDInstruments..................................................................101

8.2 ParticleCounting............................................................................................. 102

8.2.1 ElectricalCounting............................................................................ 102

8.2.2 OpticalCounting................................................................................ 102

8.2.3 TeNormalizationoCountingData............................................. 104

8.2.4 FocusedBack-ReectionMethod.................................................... 107

8.3 OpticalScatteringechniques........................................................................ 108

8.3.1 StaticLightScattering........................................................................ 108

8.3.2 DynamicLightScattering..................................................................1118.4 UltrasonicAttenuationSpectroscopy............................................................113

8.4.1 TeoreticalBackground......................................................................114

8.4.2 HardwareConsiderations...................................................................119

8.4.3 APracticalUltrasonicSpectrometer................................................121

8.4.4 Validationotheechnique.............................................................. 126

8.4.5 Applications......................................................................................... 128

8.5 AppendixonRecoveryothePSD................................................................. 135

8.6 AppendixontheX-rayDiscCentriuge....................................................... 139

9 ProcessImaging9.1 Introduction.......................................................................................................141

9.2 DirectImaging.................................................................................................. 142

9.3 omographicImaging......................................................................................143

9.4 CaseStudy:Crystallization..............................................................................147

9.5 CaseStudy:Granulation...................................................................................149

9.6 CaseStudy:MediaMilling.............................................................................. 154

10hicknessGauging10.1 RadiationGauges.............................................................................................. 159

10.2 UltrasonicTicknessGaugingoUltrathinFilms...................................... 160

10.2.1 TeoryoMeasurement......................................................................161

10.2.2 MeasurementSensitivity....................................................................163

10.2.3 EectoAmbientConditions............................................................163

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10.2.4 ransducerEects.............................................................................. 168

10.2.5 Summary.............................................................................................. 177

10.3 OpticalTicknessMeasurementsorSingleandMultilayerFilms...........178

10.3.1 PrincipleoOperation........................................................................17910.3.2 TeOpticalSensorandestBlock................................................... 180

10.3.3 SingleFilmTicknessMeasurements..............................................182

10.3.4 ApplicationtoMultilayerFilms....................................................... 184

10.4 AppendixontheTin-PlateApproximation................................................185

10.5 AppendixonDepthoFocus.......................................................................... 190

10.5.1 LaserBeamsandGaussianOptics................................................... 190

10.5.2 BeamConcentration.......................................................................... 192

10.5.3 DepthoFocus.................................................................................... 192

10.6 AppendixonTicknessCorrection............................................................... 19310.6.1 Single-PlyFilms.................................................................................. 194

10.6.2 Multi-PlyLaminates........................................................................... 195

11 PlasticsandCompositeMaterials11.1 IdentifcationoPolymerype....................................................................... 199

11.1.1 NIRAbsorbanceSpectra................................................................... 200

11.1.2 NeuralNetworks................................................................................. 202

11.1.3 HardwareImplementation................................................................ 203

11.2 ContaminationDetectioninMoltenPolymer............................................. 205

11.3 CharacterizationoReinorcedPolymers.................................................... 207

11.3.1 ApplicationsoReinorcedPolymers.............................................. 207

11.3.2 MeasurementPrinciples.................................................................... 209

11.3.3 HardwareImplementation.................................................................211

11.3.4 ExperimentalResults..........................................................................212

11.4 MeasurementoPartDimensionsUsingRadioscopy.................................214

11.4.1 Concept.................................................................................................21511.4.2 Implementation....................................................................................216

11.4.3 Depth-o-FlawMeasurements...........................................................216

11.4.4 WallTicknessMeasurements..........................................................218

11.5 AppendixontheCalculationoLoading......................................................219

Notes....................................................................................................... 223

Reerences.......... ........... .......... ........... ........... .......... ........... .......... ....... 227

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Preface

Industryusesavarietyosensorstocontrolitsoperations;themostamiliardevices

includethermocouplesandpressuregauges,whichmeasureasinglevariableatasingle

pointintheprocess.Asmanuacturingprocesseshavebecomemorecomplex,addi-

tionaltypesoinormationarerequired.ypicalprocessesnowneedmeasurementso

flmthickness,particlesize,solidsconcentration,andcontaminationdetection.Most

othesesensorsoperateonrelativelysimpleprinciplesthatarebasedontheinteractionbetweenmatterandsound,light,orelectricfelds.Tisbookexplainsthephysicsupon

whichthesemeasurementsarebasedandprovidesadditionaldetailsaboutsensoroper-

ationandinterpretationothedata.Limitsosensitivityandsignifcancearediscussed,

andexamplesareprovidedthatillustratehowthesedeviceshavebeenusedorprocess

controltoimproveproductivityorproductuniormity.

Tereisoenmorethanonetypeosensorthatwillunctionadequatelyinagiven

application.Forinstance,thegauging(thicknessmeasurement)opolyesterflmcan

beaccomplishedbyusinglight,sound,orradiation.Insuchcasesthechoiceosensor

alwaysdependsonthespecifcdetailsotheapplication,soitisimperativetounder-standtheoperationandlimitationsoeachdevice.Clearly,otheractorssuchascostor

vendorissuesneedtobeconsidered,butromapurelytechnicalpointoviewthebest

choiceosensororagivenapplicationultimatelydependsonthedetailsothemea-

surementprocess.Tepurposeothisbookistoexploretherelevantphysicsinorderto

acilitatethatchoice.

Tismonographisbasedon20yearsopersonalexperiencegainedromworking

asaphysicistinthechemicalprocessindustry,andtheexamplespresentedhereare

basedonactualinstallationsatnearlyadozensites.Separateaccountsotheseexamples

havebeenpublishedpreviously,buttheaimhereistoprovideacoherentreviewothephysicalmechanismsoprocesssensors.Tisbookwillbeointeresttoprocessowners,

chemical engineers, electrical engineers, instrumentation developers, vendors, plant

engineers,andplantoperatorsromthechemical,mineral,ood,andnuclearindustries.

Ihopethatthisinormationwillprovetobeuseulastheytackleevenmorechallenging

measurementneeds.

David M. ScottDuPont Company, Experimental Station,

Wilmington, Delaware, U.S.A.

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Acknowledgments

Tisvolumecoverssuchalongtimespanthatitisquiteimpossibletonameallothe

peoplewhohavecontributedinsomeashiontothework.ItiscertainlytruethatIowe

agreatdealtomycolleaguesattheExperimentalStation,attheDuPontplants,and

atvariousacademicinstitutionshereandabroad,butthelistwouldbelongindeed.

Ishould,however,acknowledge theolkswhocollaboratedwith metobuild andtest

thesensorsdescribedherein:ArthurBoxman,ChuckFisher,OliverGutsche,JohnHarrington,EdJochen,WouterKuiper,JerryLee,BobMoneta,LouRosen,Gregg

Sunshine,andRobertWaterland.IamalsograteultoRajeevGorowara,JohnModla,

andChristopherScottorreviewingchapterdras.Finally,Ithankmywie,Sue,orher

patienceandsupportduringthewritingothismanuscript.

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About the Author

David ScottisaphysicistattheDuPontCompanysmainresearchacilityinWilmington,

Delaware,wherehehasbeendevelopingindustrialsensorsandonlinemeasurement

applicationsortwodecades.HejoinedDuPontin1986aercompletinghisPh.D.in

atomicandmolecularphysicsattheCollegeoWilliamandMary;healsoholds the

B.A.(EarlhamCollege,1981)andM.S.(WilliamandMary,1984)degreesinphysics.He

initiallyworkedontomographyandreal-timeradiographyornondestructiveevalua-tionoadvancedcompositematerials,andlaterdevelopedopticalsensorsorindustrial

processapplications.

In1996Dr.Scottwasinvitedtoestablisharesearchgroupintheareaoparticle

characterization;sincethattime,thescopeohisgrouphasexpandedtoincludeinter-

acialengineeringandcharacterizationonanoparticlesystems.Hisprimaryresearch

interestisonlinecharacterizationoparticulatesystems,andhisresearchactivitieshave

includedprocessimaging(includingprocesstomography)andin-lineultrasonicmea-

surementoparticlesize.Heholdsseveralpatents,andhaspublishedover30technical

papersinpeer-reviewedjournals,presentedkeynoteandplenarylecturesatmanyinter-nationalconerences,andeditedseveralspecialjournalissues.

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223

Chapter 2

1. Ithedataarenotnormallydistributed(i.e.,theydonotollowtheprobabilitydis-

tributionoequation1.5),thenChebyshevsinequalitystatesthatatleast94%othe

dataallwithin4 o the meanvalue.Tis resultmeans thata deviation mustbe

twiceaslarge(comparedtothecaseonormallydistributeddata)inordertobecon-

sideredstatisticallysignicant.

2.

Seethediscussionocurrent,resistance,andvoltageinchapter5.3. Aboxcar average(alsocalledamoving average)isdenedasthemeanothelastN

readings.

Chapter 3

1. TisunitisnamedaerHeinrichHertz,whodemonstratedtheexistenceoradio

waves.

Chapter 41. Teacceptedvalueiscloseto2.998108m/s,butroundingitupto3 108m/s

simpliesthemathandintroducesonly0.1%error.

Chapter 5

1. Adiscussionovalencebandelectronsandconductionbandelectronswouldtakeus

tooarotopic.Interestedreadersshouldconsultatextbookonsolidstatephysics,

suchasKittel(2005).2. InterestedreadersshouldconsultHallidayetal.(2005),chaps.2829.

3. SeethediscussioninHorowitzandHill(1980)pp.2529.

4. Tep-typeregionissometimesdescribedashavingholesthatcanbelledbyelec-

tronsinaprocesscalledrecombination.Untiltheholesarelled,theyactasaposi-

tivechargecarrier.

5. Inacathode-raytube,thesecolorsareprovidedbydierentphosphorsthatglowred,

blueorgreenwhenstruckbytheelectronbeam;colorisdeterminedbymodulating

theintensityotheelectronbeamasitsweepsacrossthescreen.Plasmaandeld-

emissiondisplaysusedierentmethodsoaddressingeachpixel,butthey,too,excitethreetypesophosphortocreatecolor.

6. See,orexample,thediscussioninHorowitzandHill(1980),chapter3.

Notes

Copyright 2008 by Taylor and Francis Group, LLC

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224 Industrial Process Sensors

7. TisdigitizerisanAD1671ICromAnalogDevicesoNorwood,Massachusetts.

8. Forexample,theAD12401isa12-bitDACthatdigitizesat400MHz.

Chapter 6

1. Teorbitalvelocityotheelectroninahydrogenatom,orexample,isroughly2.2

106m/s(about1/137thespeedolightinvacuum).

2. See,orexample,Feynmanetal.(2006),vol.3,Lecture19.

3. TeinterestedreadercanndmoreinormationonthesedetailsinGriths(1995)

orWinter(1986).

4. Itisalsopossibleoranelectrontobecomeweaklyboundtoaneutralatom,thereby

creatingananion,whichisanegativeion.Anionsarenotconsideredhere.5. Microocustubeswithspotsizesontheorderoabout10morsmallerareavailable

ordemandingimagingapplications.

6. Largecrystalsosodiumiodideandcertainplasticsareoenusedasscintillator

material.

7. Lmaxisgenerallydeterminedbythenumberobitsusedtorepresentthegraylevelsin

theimage.Manyolderimagingsystemsuse8bits,whereLmaxis255;newersystems

use10bits(Lmax=1023)ormoretostorethegraylevel.

Chapter 7

1. Teabsenceoheatdoesnotimplytheabsenceoenergy;at0Kquantummechani-

calsystemsstillhaveazero-pointenergy.

2. See,orexample,Baker(2000),chap.12.

Chapter 8

1. Te term Coulter counter specically means a device that uses the electricalcountingmethod;itshouldnotbeconusedwithotherPSDinstrumentssoldby

Beckman-Coulter.

2. TeFBRMisavailableromMettleroledooColumbus,Ohio.

3. SeeMie(1908).AcomprehensivetreatmentotheproblemisgiveninKerker(1969).

4. SomeSLSinstrumentdesignsplacealensbeore,ratherthanaer,thesamplecell.

5. SeeorexampleKerker(1969)chap.3orIshimaru(1997)chap.2.Computerpro-

gramsorcalculatingtheMiescatteringunctionsaregivenintheappendixo

BohrenandHuman(1983).

6. DLScanalsodeterminemolecularweightandradiusogyrationinpolymersandproteins.

7. Teequationsaretoocomplextobeincludedhere;seeChallisetal.(1998).

8. Asareminder,themagnitudeoacomplexnumber ( )a ib+ ,whereiistheimaginary

number,isgivenby a b2 2+ .Strictlyspeaking,thedecibelscalemeasuresthesignal

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Notes 225

amplitudeA1withrespecttoareerencelevelA2.IA1>A2,thesignalgainequals

20 10 1 2log ( / )A A ;iA1