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VIRTUAL INSTRUMENTATION USING

LABVIEW

BY

S.ANITHA KUMARI A.P(O.G)DEPT. OF EIE


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Virtual Instrument

LabVIEW works on adata flow modelin which information

within a LabVIEW program, called a virtual instrument (VI),

flows from data sources to data sinks connected by wires.

LabVIEW supports two types of VIs--internal VIs and user

created VIs.

Internal VIs are packaged with LabVIEW and perform simple

functions like adding numbers or opening files.

User created VIs consist of both a graphical user interface

called the front panel and a code pipeline called the block

diagram.


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FRONT PANEL

Every user created VI

has a front panel that

contains the graphical

interface with which a

user interacts. The front

panel can house various

graphical objects ranging

from simple buttons to

complex graphs. It alsoincludes nonfunctioning

items such as free labels

and decorations.


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Block diagram

TheBlock Diagram is a window

where the graphical code is

created.


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Accessing the Functions

Palette in the Block

Diagram


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Popping-Up on Controls

and Indicators


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The Tool Palette

To manage, modify, and debugVI's .


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Automatic

Tool

Selection

Automatically

selects

between

the

Operate

Value,Position/Size/Select,EditTextandConnectWireTools.Itisthe

mostcommonlySelecteditemontheToolsPalette.

OperateValue ManipulatesthevaluesofFrontPanelControlsand

Indicators.GenerallyselectedwhilerunningaVI.

Position/Size/Select SelectsobjectsinaVI,movesthemandresizes

them.

EditText CreatesFreeLabelsontheFrontPanelandeditstheirtext.

Alsoedits

text

in

Owned

Labels.

ConnectWire WiresBlockDiagramnodesandobjectstogether.

ObjectShortcutMenu Displaysanobject'spopupmenuwiththeleft

mousebutton.

ScrollWindow PansthecontentonaVIwindowwithoutusingthe

window'sscrollbars.


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Set/ClearBreakpoint CreatebreakpointsinaVIBlock

Diagramfor

debugging

purposes.

Breakpoints

cause

the

VI

tosuspendexecutionataparticularpoint.

ProbeData PlacesProbesonwiresintheBlockDiagramfor

debuggingpurposes.AProbedisplaysthedataonawire

whereit

is

placed.

GetColor CopiescolorsfromVIobjectstopastingwiththe

SetColorTool.

SetColor ColorsobjectsinaVIanddisplaystheforeground

andbackground

colors

of

the

object.


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DATA TYPES

There are three possible data types in a VI

Number- This data type contains numbers thatcan be either floating point or integer.

Boolean - This data type contains logical

combinations of TRUE/FALSE, AND, OR, NOT,Etc.

String - Contains alpha-numeric characters only

All of these data types can be in either Scalar, 1DArray or 2D Array form.


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Wire Types

There are different wire colors and types that depict

what kind of data is flowing through a particular wireand if it is in Scalar, 1D Array or 2D Array form:


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Numeric Control

Representation

REPRESENTION ABBREVATION TERMINAL SIZE(BYTES)

Representation Abbreviation Terminal Size (bytes)

byte I8 1

unsigned byte U8 1

word I16 2

unsigned word U16 2

long I32 4

unsigned long U32 4

single precision SGL 4

double precision DBL 8

extend precision EXT 16


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complex single CSG 8

complex double CDB 16

complex extended CXT 32


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CHANGING

REPRESENTATIONS


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WIRING

Wires are data flow paths between Block Diagram components.

Block Diagram nodes are wired together for logical functioning of the VI.

Creatingwires:selecttheConnectWiretoolonthetoolspalette

Wire Stretching: move a wired node on the Block Diagram, thewires will stretch to follow the node

Selecting wires:

Deleting wires:


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Align and Distribute

Objects Rings

To quickly and easily make the objects on your Front Panel or Block Diagram nice

and neat.


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RUNNING VI

click on a Broken Run button,to get a list of errors in a

pop-up window


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DEBUGGING VIs

Debugging Tools on the Block Diagram Debugging Tools on the Tools Palette


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ExecutionHighlight when pressed, turns bright and allows you to view

the data flow through the Block Diagram slowly asit goes from one Block Diagram component to the

next.

StepOver activates the single-step mode which steps the

execution of the VI from node to node. Each nodeblinks then it executes one at a time.

StepInto activates the single-step mode and is used to step intoa loop or Sub VI so you can single step inside them.

StepOut used to step out of a loop or Sub VI and to end theexecution of a VI.

BreakpointTool used to set breakpoints or stopping points in a VI,especially in a Sub VIs, functions, structures and

wires.

ProbeTool

creates probes on wires in the Block Diagram. It

shows the data at that point in a wire at a particular

time. It is used for checking intermediate data inside a

VI.


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SUB VIs

The Sub VI is considered as a lower-level VIinside of an upper-level VI.

This reduces the number of Block Diagram icons, which simplifies and modularizes the VI. Sub VIsare much like functions or subroutines in conventional text-based programming languages.

Steps in creating sub vi:

create sub vi icon

Assign sub vi connectors


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STRUCTURES

In addition to controls, indicators, and VIs, the block diagram

can also contain a number of programming structures that

modify the sequence of data flow on the block diagram.

LabVIEW currently supports six different structures, -while-

loops, case structures, event structures, for-loops, sequence

structures, and formula nodes.


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WHILE LOOP

A While Loop executes all or a portion of

your Block Diagram code multiple times.

pseudo-code:

Do

Execute diagram Inside the loopWhile the condition is TRUE/FALSE

Create a While Loop

Block Diagram > Functions > Structures > While

Loop

Drag a rectangle area around the portion of Block

Diagram code that is to be included in the while

loop


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While loop components

The Conditional Terminal

Continue if True condition. thewhile loop will continue to repeat the

code until a boolean value of FALSE is

passed to the conditional terminal.

Stop if True condition. the whileloop will continue to repeat the codeuntil a boolean value of TRUE is

passed to the conditional terminal.

The Iteration Terminal

outputs the number of times the loophas been executed


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Controlling a while loop

The conditional terminal is wired to a Boolean Terminal. This terminal represents a

Boolean Control (switch) on the Front Panel for the user to control the operation of thewhile loop.


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FOR LOOP

The For Loop repeats Block Diagram code a

predetermined number of counted times.When the number of iterations equals the

predetermined count, the loop stops.

pseudo-code:

For i = 0 to N-1

Execute diagram inside the loop

Create a For Loop

Block Diagram > Functions > Structures >

For Loop:

then drag a rectangle area around the portionof Block Diagram code that is to be included

in the for loop


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For loop components

The Count TerminalThe Count Terminal is

where the predetermined

count is placed. to control

the number of iterations.

The Iteration TerminalTheIteration Terminal in a

for loop It is a terminal that

outputs the number of times

the loop has been executed.

The count starts at zero (thefirst iteration of the loop is

Iteration Zero)


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Case structures

The Case Structure is a method of

executing conditional statements. TheCase Structure is similar to if ... then ...

else statements in conventional

programming languages.

pseudo code:

If (Condition = Something) Then

Do This

Else

Do That

Endif

Case Structure is configured like a deck of cards. Labview only executes one at a

time. case executed is determined by the value wired to the selector terminal


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CASE STRUCTURE DATA TYPES


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Creating a Case Structure

Creating a Case Structure is much like creating While Loops and For Loops. To create

a Case Structure, Pop-up in the Block Diagram > Structures > Case Structure.Drag an area for the Case Structure to encompass.

Managing case structure


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The Select Function

In simple if-then-else cases, you can use the Selectfunction:

This function:

Returns the value wired to the t terminal if the value at the s terminal is TRUE

Returns the value wired to the fterminal if the value at the s terminal is

FALSE.


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SEQUENCE STRUCTURES

used to control the order of execution of nodes that are not data dependent on each other. The

nodes within each frame are data dependent The output tunnels of Sequence Structures can only have one data source which, unlike Case

Structures, has outputs that must have one data source per case. The output can come from

any frame, but the data will not leave the structure until the last frame in the structure has

completed it's execution. Data input is available to all frames. CREATING SEQUENCE STRUCTURE:Pop-up in the Block Diagram > Structures >Sequence Structure.

Toaddmoreframes,popuponthesequenceboundary>AddFrameAfter

SEQUENCE LOCAL: variablesthatallowyoutopassdatabetweenframesofaSequence

Structure


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Example for sequence local


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FORMULAE NODE

AFormulaNodeisaboxwhereyouenter

algebraicformulas

directly

into

the

Block

Diagram.Itisusefulwhenanequationis

complicatedorhasmanyvariables.


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Below is an example of how you would implement y= x^2 + x + 1 with regular block diagram nodes

It is much easier to use the Formula Node.


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CreatingaFormulaNode

Pop-up in the Block Diagram > Structures > Formula Node.

Add an Input and an Output on the left and right vertical sides of the Formula

Node's boundary. The nodes must also be named to match the variables used in the equation.

Add them by popping-up on a vertical boundary > Add Input or Add Output.

Label them correctly and wire them to the appropriate nodes.

Thentype

equation

using

the

correct

operators

and

functions.

A

semicolon

always

followseachformulastatement.


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ARRAYS

Anarrayisacollectionofdataelements. The

dataelements

in

an

array

can

be

numeric,

boolean,stringorcluster,butalldataelementsmustbeofthesametypewithinan

array.Arrays

can

be

one

or

two

dimensional.


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ARRAY FUNCTIONS

Arrays can also be created andcontrolled byArray

Functions. They are all found by

popping-up in the Block Diagram

> Functions > Array:


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ARRAY SIZE returns the number of

elements in an array it

is wired to.

INITIALIZE

ARRAY

createsanarrayof

dimensionsize

elementscontaining

theelementvalue.

BUILD ARRAY linksmultiplearrays.It

appendselements

to

anarray.

itconcatenates

multiplearrays

ARRAY SUBSET returnsaportionofan

arraystarting

at indexand

containing length elements


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ARRAY

SEARCHING

searchesthenamearray

forthe

target

and

reports

ifthetargetisfoundas

wellasitspositioninthe

array.


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Creating One-Dimensional Arrays With a Loop

Manually creating and

adding data to arrays

can be tedious work.

So loops are often

used to create one-

dimensional and two-

dimensional arrays.

Both ForLoops and

While Loops can

create arrays and their

boundaries

automatically with

auto indexing.


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Creating TWO-Dimensional Arrays With nested Loop

The outer

loop creates

the row

elements andthe inner loop

creates thecolumn

elements.


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To clear an array of data,

pop-up on any Index Display >

Empty Array:

Clearing Array Data


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INDEXING Indexing is a feature that can be enabled for input and output tunnels of both while-

loops and for-loop

When an array wire passes into a loop through a tunnel that does not have indexingenabled, the entire array is placed on the wire and can be accessed during each loop

iteration. When indexing is enabled, only the array element at the index

corresponding to the current loop iteration is available from that tunnel.s by right

clicking on a tunnel.


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INPUT INDEXING

OUTPUT INDEXING


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Polymorphism

Labview arithmetic functions like Add, Multiply,

Divide. Etc. are polymorphic. This means that

the data structures on their inputs can be either

scalar or array. If any inputs are of the array data

structure, the output will be an array data

structure. If the inputs have array structures ofdifferent sizes, the output will be an array that is

the same size as the smallest input array.


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Controlling Boolean Controls

BooleanControls

usually operate likeswitches. Most of them

are in the off position

by default (NormallyOpen). You can control

the mechanical action

of the Boolean Controlby popping-up on it >

Mechanical Action


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SwitchWhenPressed TheControl'svalueischangedeachtimethecontrolispressed.Thisworksmuchlikeastandardlightswitch.

SwitchWhenReleased TheControl'svalueischangedwhenthemouse

buttonis

released.

SwitchUntilReleased TheControl'svalueischangedwhenthecontrol

isclickedandretainsthatvalueuntilthemousebuttonisreleased.

Latch

When

Pressed

The

Control's

value

changes

when

it

is

clicked,

retainsthatvalueuntiltheVIreadsitonceandthenreverts backtoit'soriginalvalue.


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LatchWhenReleased TheControl'svaluechangeswhen

themousebuttonisreleased,retainsthatvalueuntilthe

VIreads

it

once

and

then

reverts

back

to

it's

original

value.

LatchUntilReleased TheControl'svaluechangeswhenit

isclicked,retainsthatvalueuntiltheVIreadsitonceor

untilthe

mouse

button

is

released,

whicheveroccurslast.


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Showing a Boolean

Controls State

popping up on the control >

Visible Items > Boolean Text


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THANK YOU

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