Giáo trình Introduction to LabVIEW

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IntroductiontoLabVIEW
Hans-PetterHalvorsen



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IntroductiontoLabVIEW


Hans-PetterHalvorsen
Copyright©2017


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Preface
ThisdocumentexplainsthebasicconceptsofLabVIEW.

Youfindadditionalresources,code,etc.here:

g/documents/programming/labview/






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TableofContents
Preface.....................................................................................................................................iii
TableofContents.....................................................................................................................iv
1

2

Introduction......................................................................................................................1
1.1

DataflowProgramming...............................................................................................1

1.2

GraphicalProgramming..............................................................................................1

1.3

Benefits.......................................................................................................................2

StartusingLabVIEW..........................................................................................................4
2.1

TheLabVIEWEnvironment.........................................................................................4

2.2

FrontPanel.................................................................................................................5

2.3

BlockDiagram.............................................................................................................7

2.4

ControlsPalette........................................................................................................10

2.4.1

NumericSubPalette..........................................................................................12

2.4.2

BooleanSubPalette..........................................................................................12

2.4.3

String&PathSubPalette..................................................................................13

2.5

FunctionPalette........................................................................................................13

2.6

ToolsPalette.............................................................................................................14

2.7

Wiring.......................................................................................................................16

2.8

Toolbar......................................................................................................................16

2.9

Execution..................................................................................................................17

2.10

TheObjectsshort-cutmenu.................................................................................18

2.11

DataflowProgramming.........................................................................................19

2.12

Help.......................................................................................................................20

Exercises..............................................................................................................................20
iv



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TableofContents

SubVIs.............................................................................................................................24
3.1

CreateNewSubVIfromScratch...............................................................................25

3.1.1

InputandOutputSubVIConnectors.................................................................26

3.1.2

IconEditor.........................................................................................................28

3.2

CreateSubVIfromexistingcode..............................................................................29

3.3

UsingSubVIs............................................................................................................30

Exercises..............................................................................................................................31
4

CustomizeLabVIEW.........................................................................................................33
Exercises..............................................................................................................................34

5

LoopsandStructures.......................................................................................................35
5.1

Loops.........................................................................................................................35

5.1.1

ForLoop.............................................................................................................36

5.1.2

WhileLoop........................................................................................................37

5.2

Structures.................................................................................................................38

5.2.1

CaseStructure...................................................................................................38

5.2.2

SequenceStructure...........................................................................................39

5.2.3

EventStructure..................................................................................................40

Exercises..............................................................................................................................42
6

TroubleshootingandDebugging.....................................................................................45
6.1

Howtofinderrors....................................................................................................45

6.2

HighlightExecution...................................................................................................45

6.3

Probes.......................................................................................................................46

6.4

Breakpoints...............................................................................................................47

6.5

Stepinto/over/outdebugging..................................................................................48

Exercises..............................................................................................................................48

Tutorial:AnIntroductiontoLabVIEW


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TableofContents

WorkingwithData..........................................................................................................50
7.1

Arrays........................................................................................................................50

7.1.1

Auto-Indexing....................................................................................................50

7.1.2

ArrayFunctions.................................................................................................51

7.2

Cluster.......................................................................................................................53

7.2.1

ClusterOrder.....................................................................................................54

7.2.2

ClusterElements................................................................................................55

Exercises..............................................................................................................................56
8

WorkingwithStrings.......................................................................................................58
Exercises..............................................................................................................................60

9

ErrorHandling.................................................................................................................62
9.1

FindingError.............................................................................................................62

9.2

ErrorWiring..............................................................................................................62

9.3

ErrorHandlinginSubVIs...........................................................................................63

9.4

ErrorHandling...........................................................................................................64

Exercises..............................................................................................................................65
10

WorkingwithProjects..................................................................................................66

10.1

ProjectExplorer.....................................................................................................66

10.2

Deployment...........................................................................................................67

Exercises..............................................................................................................................69
11

DesignTechniques........................................................................................................71

11.1

ForceProgramFlow..............................................................................................71

11.2

ShiftRegister.........................................................................................................72

11.3

StateProgrammingArchitecture..........................................................................73

11.4

MultipleLoops/Parallelprogramming..................................................................75

Tutorial:AnIntroductiontoLabVIEW


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11.5

TableofContents

Templates..............................................................................................................77

Exercises..............................................................................................................................78
12

UserInterface...............................................................................................................80

12.1

VIProperties.........................................................................................................81

Exercises..............................................................................................................................84
13

PlottingData.................................................................................................................85

13.1

Customizing...........................................................................................................87

Exercises..............................................................................................................................89
14

Tips&Tricks.................................................................................................................91

14.1

10functionsyouneedtoknowabout..................................................................91

14.2

The10mostusefulShort-cuts..............................................................................96

15

ExampleApplication.....................................................................................................97

16

AdditionalExercises...................................................................................................101

17

What’sNext?..............................................................................................................106

17.1

MyBlog...............................................................................................................106

17.2

Tutorials..............................................................................................................106

17.3

AdditionalResources..........................................................................................106

17.4

Examples.............................................................................................................107

QuickReference....................................................................................................................108


Tutorial:AnIntroductiontoLabVIEW




1 Introduction
LabVIEW(shortforLaboratoryVirtualInstrumentationEngineeringWorkbench)isa
platformanddevelopmentenvironmentforavisualprogramminglanguagefromNational
Instruments.Thegraphicallanguageisnamed"G".OriginallyreleasedfortheApple
Macintoshin1986,LabVIEWiscommonlyusedfordataacquisition,instrumentcontrol,and
industrialautomationonavarietyofplatformsincludingMicrosoftWindows,variousflavors
ofUNIX,Linux,andMacOSX.ThelatestversionofLabVIEWisversionLabVIEW2011.Visit
NationalInstrumentsatwww.ni.com.
Thecodefileshavetheextension“.vi”,whichisanabbreviationfor“VirtualInstrument”.
LabVIEWofferslotsofadditionalAdd-OnsandToolkits.

1.1 DataflowProgramming
TheprogramminglanguageusedinLabVIEW,alsoreferredtoasG,isadataflow
programminglanguage.Executionisdeterminedbythestructureofagraphicalblock

diagram(theLV-sourcecode)onwhichtheprogrammerconnectsdifferentfunction-nodes
bydrawingwires.Thesewirespropagatevariablesandanynodecanexecuteassoonasall
itsinputdatabecomeavailable.Sincethismightbethecaseformultiplenodes
simultaneously,Gisinherentlycapableofparallelexecution.Multi-processingandmultithreadinghardwareisautomaticallyexploitedbythebuilt-inscheduler,whichmultiplexes
multipleOSthreadsoverthenodesreadyforexecution.

1.2 GraphicalProgramming
LabVIEWtiesthecreationofuserinterfaces(calledfrontpanels)intothedevelopmentcycle.
LabVIEWprograms/subroutinesarecalledvirtualinstruments(VIs).EachVIhasthree
components:ablockdiagram,afrontpanel,andaconnectorpanel.Thelastisusedto
representtheVIintheblockdiagramsofother,callingVIs.Controlsandindicatorsonthe
frontpanelallowanoperatortoinputdataintoorextractdatafromarunningvirtual
instrument.However,thefrontpanelcanalsoserveasaprogrammaticinterface.Thusa
virtualinstrumentcaneitherberunasaprogram,withthefrontpanelservingasauser
interface,or,whendroppedasanodeontotheblockdiagram,thefrontpaneldefinesthe
inputsandoutputsforthegivennodethroughtheconnectorpane.ThisimplieseachVIcan
beeasilytestedbeforebeingembeddedasasubroutineintoalargerprogram.
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Introduction

Thegraphicalapproachalsoallowsnon-programmerstobuildprogramssimplybydragging
anddroppingvirtualrepresentationsoflabequipmentwithwhichtheyarealreadyfamiliar.
TheLabVIEWprogrammingenvironment,withtheincludedexamplesandthe

documentation,makesitsimpletocreatesmallapplications.Thisisabenefitononeside,
butthereisalsoacertaindangerofunderestimatingtheexpertiseneededforgoodquality
"G"programming.Forcomplexalgorithmsorlarge-scalecode,itisimportantthatthe
programmerpossessanextensiveknowledgeofthespecialLabVIEWsyntaxandthe
topologyofitsmemorymanagement.ThemostadvancedLabVIEWdevelopmentsystems
offerthepossibilityofbuildingstand-aloneapplications.Furthermore,itispossibletocreate
distributedapplications,whichcommunicatebyaclient/serverscheme,andaretherefore
easiertoimplementduetotheinherentlyparallelnatureofG-code.

1.3 Benefits
OnebenefitofLabVIEWoverotherdevelopmentenvironmentsistheextensivesupportfor
accessinginstrumentationhardware.Driversandabstractionlayersformanydifferenttypes
ofinstrumentsandbusesareincludedorareavailableforinclusion.Thesepresent
themselvesasgraphicalnodes.Theabstractionlayersofferstandardsoftwareinterfacesto
communicatewithhardwaredevices.Theprovideddriverinterfacessaveprogram
developmenttime.ThesalespitchofNationalInstrumentsis,therefore,thatevenpeople
withlimitedcodingexperiencecanwriteprogramsanddeploytestsolutionsinareduced
timeframewhencomparedtomoreconventionalorcompetingsystems.Anewhardware
drivertopology(DAQmxBase),whichconsistsmainlyofG-codedcomponentswithonlya
fewregistercallsthroughNIMeasurementHardwareDDK(DriverDevelopmentKit)
functions,providesplatformindependenthardwareaccesstonumerousdataacquisition
andinstrumentationdevices.TheDAQmxBasedriverisavailableforLabVIEWonWindows,
MacOSXandLinuxplatforms.
Thisdocumentintroducingthefollowingthemes:
•

•
•
•
•

StartusingLabVIEW
o TheLabVIEWEnvironment
o FrontPanelandBlockDiagram
o Palettes:ControlPalette,FunctionsPalette,ToolsPalette
o DataTypes
o PropertyNodes
SubVIs
LoopsandStructures
TroubleshootingandDebugging
WorkingwithData
Tutorial:AnIntroductiontoLabVIEW


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•
•
•
•

•
•
•
•

•

•

o Arrays
§ ArrayFunctions
o Cluster
WorkingwithStrings
ErrorHandling
WorkingwithProjectsusingProjectExplorer
DesignTechniques
o ShiftRegister
o StateMachine
o MultipleLoops
UserInterface
PlottingData
Deployment:BuildingExecutableApplications(.exe)
IntroductiontoAdd-OnsandToolkits
o Brieflyexplanations…
o MoredetailaboutControlandSimulationModuleinlater
IntroductiontoDAQ-DataAcquisition
o MAX–MeasurementandAutomationExplorer
o NI-DAQmx
QuickReferencewithKeyboardShort-cuts



FormoreinformationaboutLabVIEW,visitmyBlog:

g

Tutorial:AnIntroductiontoLabVIEW

Introduction




2 StartusingLabVIEW
ThischapterexplainsthebasicconceptsinLabVIEW.
Thetopicsareasfollows:
•
•
•
•
•

TheLabVIEWEnvironment
FrontPanelandBlockDiagram
Palettes:ControlPalette,FunctionsPalette,ToolsPalette
DataTypes
PropertyNodes

2.1 TheLabVIEWEnvironment
LabVIEWprogramsarecalledVirtualInstruments,orVIs,becausetheirappearanceand
operationimitatephysicalinstruments,suchasoscilloscopesandmultimeters.LabVIEW
containsacomprehensivesetoftoolsforacquiringanalyzing,displaying,andstoringdata,as
wellastoolstohelpyoutroubleshootyourcode.
WhenopeningLabVIEW,youfirstcometothe“GettingStarted”window.


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StartusingLabVIEW

InordertocreateanewVI,select“BlankVI”orinordertocreateanewLabVIEWproject,
select“Emptyproject”.
WhenyouopenablankVI,anuntitledfrontpanelwindowappears.Thiswindowdisplays
thefrontpanelandisoneofthetwoLabVIEWwindowsyouusetobuildaVI.Theother
windowcontainstheblockdiagram.Thesectionsbelowdescribethefrontpanelandthe
blockdiagram.

2.2 FrontPanel
WhenyouhavecreatedanewVIorselectedanexistingVI,theFrontPanelandtheBlock
DiagramforthatspecificVIwillappear.


InLabVIEW,youbuildauserinterface,orfrontpanel,withcontrolsandindicators.Controls
areknobs,pushbuttons,dials,andotherinputdevices.Indicatorsaregraphs,LEDs,and
otherdisplays.
Youbuildthefrontpanelwithcontrolsandindicators,whicharetheinteractiveinputand
outputterminalsoftheVI,respectively.Controlsareknobs,pushbuttons,dials,andother
inputdevices.Indicatorsaregraphs,LEDs,andotherdisplays.Controlssimulateinstrument

Tutorial:AnIntroductiontoLabVIEW

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StartusingLabVIEW

inputdevicesandsupplydatatotheblockdiagramoftheVI.Indicatorssimulateinstrument
outputdevicesanddisplaydatatheblockdiagramacquiresorgenerates.
E.g.,a“Numeric”caneitherbea“NumericControl”ora“NumericIndicator”,asseenbelow.


Iyouselecta“NumericControl”,itcaneasybechangedtoan“NumericIndicator”byright
clickontheobjectanselect“ChangetoIndicator”


Oropposite,Iyouselecta“NumericIndicator”,itcaneasybechangedtoan“Numeric
Control”byrightclickontheobjectanselect“ChangetoControl”

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StartusingLabVIEW

Thedifferencebetweena“NumericControl”anda“NumericIndicator”isthatfora
“NumericControl”youmayenteravalue,whilethe“NumericIndicator”isread-only,i.e.,
youmayonlyreadthevalue,notchangeit.


Theappearanceisalsoslightlydifferent,the“NumericControl”hasanincrementandan
decrementbuttoninfront,whilethe“NumericIndicator”hasadarkerbackgroundcolorin
ordertoindicatethatitsread-only.

2.3 BlockDiagram
Afteryoubuildtheuserinterface,youaddcodeusingVIsandstructurestocontrolthefront
panelobjects.Theblockdiagramcontainsthiscode.Insomeways,theblockdiagram
resemblesaflowchart.

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StartusingLabVIEW



Afteryoubuildthefrontpanel,youaddcodeusinggraphicalrepresentationsoffunctionsto
controlthefrontpanelobjects.Theblockdiagramcontainsthisgraphicalsourcecode.Front
panelobjectsappearasterminals,ontheblockdiagram.Blockdiagramobjectsinclude
terminals,SubVIs,functions,constants,structures,andwires,whichtransferdataamong
otherblockdiagramobjects.

TheFigurebelowshowsafrontpanelanditscorrespondingblockdiagramwithfrontpanel
andblockdiagramcomponents.

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StartusingLabVIEW


Thedifferentcomponentsareasfollows:
1. Toolbar
2. OwnedLabel
3. NumericControl
4. FreeLabel
5. NumericControlTerminal
6. KnobTerminal
7. NumericConstant
8. MultiplyFunction
9. Icon
10. KnobControl
11. PlotLegend
12. XYGraph
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StartusingLabVIEW

13. WireDataPath
14. XYGraphTerminal
15. BundleFunction
16. SubVI
17. ForLoopStructure

2.4 ControlsPalette
TheControlsandFunctionspalettescontainsubpalettesofobjectsyoucanusetocreatea
VI.Whenyouclickasubpaletteicon,theentirepalettechangestothesubpaletteyou
selected.Touseanobjectonthepalettes,clicktheobjectandplaceitonthefrontpanelor
blockdiagram.TheControlspaletteisavailableonlyonthefrontpanel.TheControlspalette
containsthecontrolsandindicatorsyouusetobuildthefrontpanel.


ThemostusedSubPalettesaretheNumericSubPalette,theBooleanSubPaletteandthe
String&PathSubPalette.
YoumaychangetheappearanceandthecontentsoftheControlspalette:

Tutorial:AnIntroductiontoLabVIEW


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StartusingLabVIEW

YoumayPinthepalette,soitisalwaysvisible,justclickthelittlepinbutton
upperleftcornerofthepalette:

inthe


Ifyouwanttochangethecontentandappearanceofthepalette,clickthe“View”button.


Hereyoumaychangethewaythepaletteshouldlook.


Ifyouclick“ChangeVisibleCategories…”youmaychangewhichCategoriesyouwanttohave
visible.



Tutorial:AnIntroductiontoLabVIEW


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2.4.1



StartusingLabVIEW

NumericSubPalette

“NumericalControl”and“NumericalIndicator”arethemostusedobjectsinthenumericsub
palette.



2.4.2

BooleanSubPalette

Thispalettehaslotsofdifferentbuttonsyoumayuse.OK,CancelandStopbuttonsare
useful.

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StartusingLabVIEW



2.4.3

String&PathSubPalette

IntheStringandPathpalettewehaveStringControls,ComboBox,etc.

2.5 FunctionPalette
TheFunctionspaletteisavailableonlyontheblockdiagram.TheFunctionspalettecontains
theVIsandfunctionsyouusetobuildtheblockdiagram.

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StartusingLabVIEW



2.6 ToolsPalette
Youcancreate,modify,anddebugVIsusingthetoolslocatedonthefloatingToolspalette.
TheToolspaletteisavailableonboththefrontpanelandtheblockdiagram.Atoolisa
specialoperatingmodeofthemousecursor.Thecursorcorrespondstotheiconofthetool
selectedintheToolspalette.Usethetoolstooperateandmodifyfrontpanelandblock
diagramobjects.

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StartusingLabVIEW


TheToolspaletteisavailablefromtheViewmenu:


Ifyoumakesure“Automaticwiring”isdisabled(Irecommendyoudoso!)youmayuse
theTabkeyonyourkeyboardinordertoswitchbetweenthemostcommontools.
Themostusedtoolsare:
UsetheOperatingtool,shownatleft,tochangethevaluesofacontrolorselect
thetextwithinacontrol.TheOperatingtoolchangestotheiconshownatleftwhenit
movesoveratextcontrol,suchasanumericorstringcontrol.
UsethePositioningtool,shownatleft,toselect,move,orresizeobjects.The
Positioningtoolchangestoresizinghandleswhenitmovesovertheedgeofaresizable
object.
UsetheLabelingtool,shownatleft,toedittextandcreatefreelabels.The
Labelingtoolchangestothefollowingicon

whenyoucreatefreelabels.

UsetheWiringtool,shownatleft,towireobjectstogetherontheblockdiagram.

Tutorial:AnIntroductiontoLabVIEW


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StartusingLabVIEW

2.7 Wiring
InordertocreatethelogicalflowbetweentheobjectontheBlockDiagram,youneedtouse
theWiringtoolinordertoconnectthedifferentobjectstogether.
UsetheWiringtooltowireobjectstogetherontheblockdiagram.
AvailableKeyboardShortcutswhendealingwithWiring:


Ctrl-Bisveryuseful.Thisshort-cutremovesallbrokenwiresontheBlockDiagram.

2.8 Toolbar
BelowweseetheLabVIEWToolbar:

Thebehaviorsofthedifferentbuttonsareasfollows:

Tutorial:AnIntroductiontoLabVIEW


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StartusingLabVIEW

ClicktheRunbuttontorunaVI.LabVIEWcompilestheVI,ifnecessary.YoucanrunaVI
iftheRunbuttonappearsasasolidwhitearrow.Thesolidwhitearrow,shownabove,also
indicatesyoucanusetheVIasasubVIifyoucreateaconnectorpanefortheVI.
WhiletheVIruns,theRunbuttonappearsasshownatleftiftheVIisatop-levelVI,

meaningithasnocallersandthereforeisnotasubVI.
IftheVIthatisrunningisasubVI,theRunbuttonappearsasshownatleft.
TheRunbuttonappearsbroken,shownatleft,whentheVIyouarecreatingorediting
containserrors.IftheRunbuttonstillappearsbrokenafteryoufinishwiringtheblock
diagram,theVIisbrokenandcannotrun.ClickthisbuttontodisplaytheErrorlistwindow,
whichlistsallerrorsandwarnings.
ClicktheRunContinuouslybutton,shownatleft,toruntheVIuntilyouabortorpause
execution.Youalsocanclickthebuttonagaintodisablecontinuousrunning.
WhiletheVIruns,theAbortExecutionbutton,shownatleft,appears.Clickthisbutton
tostoptheVIimmediatelyifthereisnootherwaytostoptheVI.Ifmorethanonerunning
top-levelVIusestheVI,thebuttonisdimmed.
Note:AvoidusingtheAbortExecutionbuttontostopaVI.EitherlettheVIcompleteitsdata
owordesignamethodtostoptheVIprogrammatically.Bydoingso,theVIisataknown
state.Forexample,placeabuttononthefrontpanelthatstopstheVIwhenyouclickit.
ClickthePausebutton,shownatleft,topausearunningVI.WhenyouclickthePause
button,LabVIEWhighlightsontheblockdiagramthelocationwhereyoupausedexecution,
andthePausebuttonappearsred.ClickthebuttonagaintocontinuerunningtheVI.

2.9 Execution
InadditiontotheToolbarbuttonsabovethefollowingKeyboardShortcutsareavailable
whendealingwithExecution:


Tutorial:AnIntroductiontoLabVIEW


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StartusingLabVIEW



2.10

TheObjectsshort-cutmenu

Themostoften-usedmenuistheobjectshortcutmenu.AllLabVIEWobjectsandempty
spaceonthefrontpanelandblockdiagramhaveassociatedshortcutmenus.Usethe
shortcutmenuitemstochangethelookorbehavioroffrontpanelandblockdiagram
objects.Toaccesstheshortcutmenu,right-clicktheobject,frontpanel,orblockdiagram.
TheNumericcontrolhasthefollowingshort-cut/right-clickmenu:


Theshort-cutmenuwillbedifferentforthedifferentcontrolsorobjects.

Tutorial:AnIntroductiontoLabVIEW