PC Interfacing and Data Acquisition This Page Intentionally Left Blank PC Interfacing and Data Acquisition: Techniques for Measurement, Instrumentation and Control Kevin James Newnes OXFORD AUCKLAND BOSTON JOHANNESBURG MELBOURNE NEWDELHI Newnes AnimprintofButterworth-Heinemann LinacreHouse,JordanHill,OxfordOX28DP 225WildwoodAvenue,Woburn,MA01801-2041 AdivisionofReedEducationalandProfessionalPublishingLtd Firstpublished2000 ©KevinJames2000 Allrightsreserved.Nopartofthispublicationmaybereproducedin anymaterialform(includingphotocopyingorstoringinanymediumby electronicmeansandwhetherornottransientlyorincidentallytosome otheruseofthispublication)withoutthewrittenpermissionofthe copyrightholderexceptinaccordancewiththeprovisionsoftheCopyright, DesignsandPatentsAct1988orunderthetermsofalicenceissuedbythe CopyrightLicensingAgencyLtd,90TottenhamCourtRoad,London, EnglandW1P9HE.Applicationsforthecopyrightholder’swritten permissiontoreproduceanypartofthispublicationshouldbeaddressed tothepublishers BritishLibraryCataloguinginPublicationData AcataloguerecordforthisbookisavailablefromtheBritishLibrary ISBN0750646241 TypesetbyLaserWords,Madras,India PrintedandboundinGreatBritain Contents Preface ix Anoteonsoftwareexamples x Part1:IntroductiontoDataAcquisitiononthePC 1 ThePCasaplatformfordataacquisition 3 1.1 TypesofPC 4 1.2 Theprocessor 5 1.3 Memory 11 1.4 Input/outputports 15 1.5 Busesandadaptorcardslots 17 2 Softwareconsiderations 26 2.1 AnoverviewofDA&Csoftware 26 2.2 Dataacquisitionandcontrolinrealtime 30 2.3 Implementingreal-timesystemsonthePC 45 2.4 Robustness,reliabilityandsafety 61 Part2:SamplingFundamentals 3 Sensorsandinterfacing 71 3.1 Introduction 71 3.2 DigitalI/O 76 3.3 Sensorsforanaloguesignals 81 3.4 Handlinganaloguesignals 95 3.5 Digitizationandsignalconversion 103 3.6 Analoguemeasurements 124 3.7 Timersandpacing 128 4 Sampling,noiseandfiltering 131 4.1 Samplingandaliasing 131 4.2 Noiseandfiltering 142 vi Contents Part3:I/OTechniquesandBuses 5 Theinterruptsystem 163 5.1 Interruptvectors 164 5.2 Hardwareinterrupts 169 5.3 Softwareinterruptsandprocessorexceptions 185 5.4 Interruptpriorities 189 5.5 Writinginterrupthandlers 190 5.6 Re-entrancyandaccessingsharedresources 199 5.7 Interruptresponsetimes 200 6 Datatransfer 205 6.1 Data-acquisitioninterfacedevices 205 6.2 Datatransfertechniquesandprotocols 211 6.3 BuffersandbufferedI/O 244 7 Parallelbuses 251 7.1 Introduction 252 7.2 Dataacquisitionusingaparallelbus 253 7.3 ThePC’sparallelport 254 7.4 TheIEEE-488(GPIB)bus 270 8 Serialcommunications 284 8.1 Somecommonterms 284 8.2 Introductiontoasynchronouscommunication 286 8.3 Dataacquisitionviaaseriallink 291 8.4 Serialinterfacestandards 296 8.5 AsynchronousserialI/OonthePC 308 Part4:InterpretingandUsingAcquiredData 9 Scalingandlinearization 345 9.1 Scalingoflinearresponsecurves 346 9.2 Linearization 356 9.3 Polynomiallinearization 357 9.4 Interpolationbetweenpointsinalook-uptable 373 9.5 Interpolationvs.power-seriespolynomials 381 9.6 Interactivecalibrationprograms 381 9.7 Practicalissues 383 10 Basiccontroltechniques 387 10.1 Terminology 387 10.2 Anoverviewofcontrolsystems 388 10.3 Programmablelogiccontrollers 390 10.4 Safetyandreliabilityofcontrolsystems 391 10.5 Discontinuouscontrolsystems 392 10.6 Continuouscontrolsystems 396 Contents vii Part5:Examples 11 Exampleprojects 411 11.1 Dimensionalgaugingofrailwaycarriagewheels 411 11.2 In-situsensorcalibrationonatube-straightening machine 413 11.3 Dimensionalgaugingofturbineblades 416 11.4 Torsionalrigiditytestingofcarbodies 420 11.5 Winchtestingsystem 423 11.6 Brakeactuatortestsystem 426 11.7 Monitoringofbush-insertionload 429 11.8 Laboratoryfurnacetemperaturecontrol 432 11.9 Thermoluminescencespectrometry 434 Part6:Appendices AppendixA Adaptorinstallationreference 441 AppendixB Charactercodes 447 References 453 Index 457 This Page Intentionally Left Blank Preface Untilfairlyrecentlymostscientificdata-gatheringsystemsandindus- trial control procedures were based on electromechanical devices such as chart recorders and analogue gauges. The capability to processandanalysedatawasratherlimited(andinsomecaseserror prone) unless one had access to a minicomputer or mainframe. Today,thatsituation haschangedconsiderably.I amsurethatmost potential readers of this book will be aware of the profound effect thePChashadonthewayinwhichengineersandscientistsareable toapproachdata-gatheringtasks. Despite the now widespread use of various types of PC for automated data capture, there has been only a small number of publications on PC-based DA&C. Most if not all of these texts have concentrated on the hardware aspects of interfacing and measure- ment. A book emphasizing the design of DA&C software is long overdue. One of the reasons for this has become increasingly apparent to me during the course of writing the present text. The subject spans numerous conventional disciplines and no single book can really do full justice to every aspect of this interdisciplinary subject. DA&C programming tends to require skills in (or at least a basic knowledge of) a range of subjects and, for this reason, the book draws together elements of programming, PC architecture, oper- ating systems, interfacing, communications, sampling theory and processcontrol. My task has been complicated because of the wide range of backgrounds from which DA&C programmers tend to originate. Amongst the readership there will, no doubt, be fairly experienced programmers as well as engineers and scientists whose main area of expertise lies in fields other than computer programming. Some readerswillalreadyhaveasoundknowledgeofdataacquisition,while for others the principles of interfacing, measurement and control will be relatively new. With such a broad spectrum of potential