Virtual instrumentation (LabVIEW)

Course Name :Virtual Instrumentation
Course Code: AEI-802
6 May 2015 1
Subject Incharge:
Ms. Princy Randhawa
Assistant Professor

Introduction
What is an Instrument?
 Collect the data
Analysis Data
Display Information
e.g. Transducer, Oscilloscopes, Digital
Multi-meter
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Virtual Instrumentation- Definition
 To Test, Control and Design
applications making accurate analog
and digital measurements.
 Using VI, can also control external
hardware devices from desktop
computer and for displaying unit.
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Virtual Instrumentation Model
Design
(Modeling/Simulat
ion)
Prototype Deployment
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ResultsAnalysis/Control
Data Acquisition
(Reference Data)

Virtual Instrumentation-Architecture
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Sensor Module
Sensing (or Transducer)
Signal conditioning
A/D conversion
Processing Module
Sensor Interface
Data Base
Interface
Medical
Information
System
Interface
User Interface-Display and Control

Historical Perspective
Analog Measurement Devices
Data Acquisition and Processing
Devices
Digital processing based on general
purpose computing platform
Distributed virtual instrumentation
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Distributed Virtual Instrumentation
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Internet
Information
System Interface
Private
Networks
Mobile
Telephony
WAP
Gateway
Extranet
SMS Gateway

Contd…
 Medical Information System Networks
and Private Networks
 Medical information systems, such as hospital
information systems, are usually integrated as Intranets
using Local Area Network (LAN).
 Advanced virtual instrumentation solutions could be
implemented using existing local and private networks.
6 May 2015 8

Contd…
 Internet
 Various remote devices, such as tele-robots or remote
experimental apparatus, can be directly controlled from
the Internet.
Many of virtual instrumentation development tools, such
as Lab VIEW, directly support integration of virtual
instruments in the Internet environment.
6 May 2015 9

Contd…
 Cellular Networks
 Wireless Access Protocol (WAP) is platform-independent
wireless technology, which enables mobile devices to effectively
access Internet content and services, as well as to communicate
with each other.
 Emergency WAP push, which sends WML messages to
physicians or medical call enter in case of medical emergency.
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Traditional Vs Virtual Instruments
Traditional Instruments Virtual Instruments
Vendor-defined User-defined
Function-specific, stand-alone with
limited connectivity
Application-oriented system with
connectivity to networks, peripherals,
and applications
Hardware is the key Software is the key
Expensive Low-cost, reusable
Closed, fixed functionality Open, flexible functionality leveraging
off familiar computer technology
Slow turn on technology (5–10 year life
cycle)
Fast turn on technology (1–2 year life
cycle)
Minimal economics of scale Maximum economics of scale
High development and maintenance
costs
Software minimizes development and
maintenance costs
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Advantages of VI
 Performance
 Platform-Independent Nature
 Flexibility
 Lower Cost
 Plug-In and Networked Hardware
 The Costs of a Measurement Application
 Reducing System Specification Time Cost
 Lowering the Cost of Hardware and Software
 Minimizing Set-Up and Configuration Time Costs
 Decreasing Application Software development
Time Costs
6 May 2015 12

LABVIEW-Introduction
 Laboratory Virtual Instrument Engineering
Workbench (Lab VIEW)
 Lab VIEW 1.0 was launched in 1986.
 Lab VIEW is a graphical programming language (G)
that uses icons instead of lines of text to create
applications.
 Lab VIEW Programs Are Called Virtual Instruments
(VIs) because their appearance and operation imitate
physical instruments like Oscilloscopes, Digital
Multi-meter.
 Lab VIEW contains a set of VIs and functions for
acquiring , analyzing , displaying and storing data.
6 May 2015 13

Contd…
 It includes analysis functions for differential
equations, optimization, curve fitting, calculus,
linear algebra, statistics and so on.
 It also includes the tools to present the data on the
computers: Charts, Graphs, Tables, Gauges,
Meters,Tanks,3D controls, 3D Graphs, Picture
Control etc.
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Using Lab VIEW in the Real World
 Lab VIEW can command plug-in data acquisition, or DAQ,
devices to acquire or generate analog and digital signals
 Using DAQ devices and Lab VIEW to monitor a
temperature, send signals to an external system, or determine
the frequency of an unknown signal.
 Lab VIEW also facilitates data transfer over the General
Purpose Interface Bus (GPIB), or through your computer's
built-in USB, Ethernet, Firm wire (also known as IEEE 1394),
or serial port.
 GPIB is frequently used to communicate with oscilloscopes,
scanners, and multi meters, and to drive instruments from
remote locations.
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Contd….
6 May 2015 16
Figure 1.1 The Space Industries Sheet Float Zone Furnace is used for high-
temperature superconductor materials processing research in a microgravity
environment aboard the NASA KC-135 parabolic aircraft. Lab VIEW controls the
industrialized Mac OS-based system.

Advantages of LAB VIEW
 Graphical User Interface
 Easy to use and Learn
 Drag and Drop built-in functions
 Modular Design and hierarchical design
 Multiple high level development tools
 Professional Development tools
 Multi platforms
 Reduces Cost and preserves investment
 Flexibility and scalability
 Connectivity and Instrument control
 Open Environment
 Distributed Development
 Visualization capabilities
 Rapid development with express technology
 Compiled language for fast execution
 Simple application distribution
 Target management
 Object Oriented Design
 Algorithm Design
6 May 2015 17

Virtual Instrumentation in the
Engineering process
6 May 2015 18
Development
Test and
Validation
Research and
Design
Manufacturing
Test
Manufacturing

Comparison of Text Based and
Graphical Programming
Text Based Programming Graphical Programming
Syntax must be known to do programming Syntax is knowledge but is not required for
programming
The execution of the program is from top to
bottom
The execution of the program is from left to
right
To check for the error the program has to be
compiled or executed
Errors are indicated as we wire the blocks
Front panel design needs extra coding or
needs extra work
Front panel design is a part of programming
Text based programming is not interactive Graphical programming is highly interactive
This is the text based programming where
the programming is not conventional
method
The programming is data flow programming
Logical error finding is easy in large
programs
Logical error finding in large programs is
quiet complicated
Program flow is not visible Data flow is visible
It is Text based Programming It is icon based programming and wiring
Passing parameters to sub routine is difficult Passing Parameters to sub VI is easy
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Lab VIEW Terms and Their
Conventional Equivalents
Lab VIEW Conventional Language
VI Program
Function Function or Method
Sub VI Subroutine, Sub Program or
Object
front panel user interface
Block Diagram Program Code
G C, C++, Java, Pascal, BASIC, etc.
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Lab VIEW Programs Are Called
Virtual Instruments (VIs)
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 Front Panel
•Controls = Inputs
•Indicators = Outputs
 Block Diagram
•Accompanying “program” for front panel
•Components “wired” together

Front Panel
 The front panel is the user interface of the VI. You
build the front panel with controls and indicators,
which are the interactive input and output
terminals of the VI, respectively.
 Controls are knobs, push buttons, dials, and other
input devices. Indicators are graphs, LEDs, and
other displays.
 Controls simulate instrument input devices and
supply data to the block diagram of the VI.
Indicators simulate instrument output devices and
display data the block diagram acquires or
generates.
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Lab VIEW front panel
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Block Diagram
 Every control or indicator on the front panel has a
corresponding terminal on the block diagram.
 It contains-Terminals, Nodes, Wires
 Wires connect each of the nodes on the block diagram,
including control and indicator terminals, functions and
structures.
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Node
Wire
Terminal

Basic wires used in block diagrams
and corresponding types
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Each wire has different style or color, depending on the data
type that flows through the wire:

Tools Palette
 The Tools palette is available on the front panel and the block
diagram.
 A tool is a special operating mode of the mouse cursor. When
you select a tool, the cursor icon changes to the tool icon.
 Use the tools to operate and modify front panel and block
diagram objects.
 Select View» Tools Palette from the taskbar to display the
Tools palette.
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Controls Palette
 The Controls palette is only available on the front panel. The
Controls palette contains the front panel controls and
indicators you use to create the user interface.
 Select View» Controls Palette or right-click the front panel
workspace to display the Controls palette.
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Functions Palette
 The Functions palette is available only on the block diagram.
The Functions palette contains the objects you use to program
your VI, such as arithmetic, instrument I/O, file I/O, and
data acquisition operations.
 Select View» Functions Palette from the taskbar or right-click
the block diagram workspace to display the Functions
palette.
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Status Toolbar
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Run Button
Continuous Run Button
Abort Execution
Pause Button
Text Settings
Align Objects
Distribute Objects
Reorder
Resize front panel objects
Execution Highlighting Button
Step Into Button
Step over Button
Step Out Button

Types of Controls and Indicators
6 May 2015 30

Data flow programming
Block diagram does NOT execute left to right
Node executes when data is available to ALL input
terminals
Nodes supply data to all output terminals when
done
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Keyboard Shortcuts while
working with Lab VIEW
 <Ctrl-S > Save a VI
 <Ctrl-R> Run a VI
 <Ctrl-F> Find object
<Ctrl-H> – Activate/Deactivate Context Help
Window
<Ctrl-B> – Remove Broken Wires From Block
Diagram
<Ctrl-E> – Toggle Between Front Panel and Block
Diagram
 <Ctrl-Z> – Undo (Also in Edit Menu)
6 May 2015 32

Examples
☺ Divide two numbers and find the remainder
and quotient.
☺ Convert Celsius to Fahrenheit.
☺ Find whether the given number is odd or
even.
☺ Convert a binary number to a decimal
number.
☺Compute the given equations (X1+2)*log(X1)
using functions, Expression node and Express
formula for the given inputs.
☺Add two binary numbers and find the sum
and carry( half adder).
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Creating SUBVIs
 A SubVI is a VI that can be used within another VI
 Advantages
◦ Modular
◦ Easier to debug
◦ Don’t have to recreate code
◦ Require less memory
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Icon and Connector
6 May 2015 35
Icon
Connector
Terminals
An icon represents a VI in other block
diagrams
A connector shows available terminals for
data transfer

Steps to Create SubVI
Create the Icon
Create the Connector
Assign Terminals
Save the VI
Insert the VI into a Top Level VI
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Create the icon
6 May 2015 37
Right-click on the icon in the diagram or front panel

Create the Connector
6 May 2015 38
Right click on the icon pane (front panel only)

Assign Terminals
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Saving the VI
 Choose an Easy to Remember Location
 Organize by Functionality
◦ Save Similar VIs into one directory (e.g. Math Utilities)
 Organize by Application
◦ Save all VIs Used for a Specific Application into one
directory or library file (e.g. Lab 1 – Frequency Response)
◦ Library Files (.llbs) combine many VI’s into a single file,
ideal for transferring entire applications across computers
6 May 2015 40

Examples
 Create a VI to find the average of two
numbers and convert a section of VI
into SubVI.
Create a VI to find roots of a quadratic
equation using SubVIs . Find both the
values of roots and the nature of roots.
6 May 2015 41

Programming Concepts of VI
 Control Structures- For Loop and While Loop
 Shift Registers and their functions
 Feedback Nodes
 Structures- Sequence and Case Structure
 Formula Node
 Arrays- Single and Multidimensional Array
Auto-indexing of Arrays
Functions for Manipulating Arrays
 Creating Clusters Controls and Indicators
 Waveform Charts
 Single plot and Multiple Plot Waveform Graphs
 XY Graphs and Intensity Graphs
 Strings ,String Functions
 File Input/output, File I/O Vis Functions
6 May 2015 42

Loops
 Nearly all programs involve some sort of loop where all or
sections of the program must be repeated.
 Both the While and For Loops are located on the Functions»
Structures palette.
 The For Loop differs from the While Loop in that the For
Loop executes a set number of times.
 A While Loop stops executing the sub diagram only if the
value at the conditional terminal exists.
6 May 2015 43FOR Loop While Loop

Drawing Loops
 Select the structure required
 Enclose the code to be
repeated (looped)
 Wire the appropriate loop
conditions
o Runs according to input N number of
iterations
o Counts the number of iterations
6 May 2015 44

LAB VIEW Functions
 What types of function are available
◦ Analysis
 Signal processing
 Statistics
 Advanced math &
formulae
◦ Storage
 File I/O
 Zip
◦ ARM specific
 Simulation
 Read digital I/O
◦ +Many more!
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Wait Functions
6 May 2015 46
Wait until next ms Multiple
Functions» Time & Dialog palette

Contd….
6 May 2015 47
Wait (ms)
Functions»Time & Dialog palette
Time Delay
Functions»Time & Dialog palette

Accessing Previous Loop Data – Shift
Register
 Available at left or right border of loop structures
 Right-click the border and select Add Shift Register
 Right terminal stores data on completion of iteration
 Left terminal provides stored data at beginning of next
iteration
6 May 2015 48
Value 3
First Iteration Second Iteration Last Iteration
Initial Value
Before Loop
Begins

Additional Shift Register Elements
6 May 2015 49
Right-click the
left terminal
to add new
elements
Right-click the border
for a new shift register

Feedback Nodes
 Appears automatically in a For Loop or While
Loop if you wire the output of a subVI, function, or
group of subVIs and functions to the input of that
same VI, function, or group.
 Stores data when the loop completes an iteration,
sends that value to the next iteration of the loop,
and transfers any data type
6 May 2015 50

Contd…
6 May 2015 51
Wire from output to input to automatically create a feedback node
OR
 Place a feedback node from the Functions»Structures palette

Local and Global Variables
Local Variable allows you to read or
write to a control or indicator on the
front panel.
It allows you to force a control’s value
with the code, or use an indicator to
store data.
 It can store all types of data, such as
numeric values, strings, T/F values,
or arrays
6 May 2015 52

Contd….
A Global variable is identical in function to
a local variable. The difference between
them is where the data is saved.
A local variable saves the data to the front
panel of the VI that it’s in; this makes them
only be useable in that VI.
A global variable is used to pass
information from one VI to another
6 May 2015 53

Contd…
 Global variable is located under structure
 The global variable only has a front panel with no
block diagram
*if a certain data type is needed, the indicator
representation must be changed within the Global
Variable VI
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Encode Message Program
6 May 2015 55

Select a Global Variable that is
already created
 In order to select a Global Variable that has already been
created, right click on the block diagram and select “select a
VI”
 Locate the created Global Variable and place it on the block
diagram
6 May 2015 56

Decode Message Program
6 May 2015 57

Examples
 Create a VI to find the factorial of the given number using
FOR loop and While Loop
 Create a VI to find the sum of first n natural numbers using a
while loop with a feedback node.
 Create a VI to change the state of the Boolean indicator n
times between TRUE and FALSE.
 Create a Global VI which consists of a knob and a stop
button. Create another VI consisting of a waveform chart.
Update the values of Global Vis knob and plot Vis side in the
waveform chart. Press the stop button of the Global VI to stop
both the Vis.
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Arrays
6 May 2015 59
An array is like a list.
An array is a collection of elements
 All elements in the array have the
same data type: Boolean, Double,
Int, String

Thinking About Arrays
Index 0 1 2 3 4 5 6 7
Element 2.4 5 6.7 4.8 1.4 3.6 7.4 1.3
6 May 2015 60
 Array elements are accessed by their
index
 Indices start at 0, not 1
 This is a one dimensional array
Arrays can have more dimensions
2 dimensional array, like a table of
data

Arrays in LabVIEW
Arrays can be created
on the block diagram
On block diagram select
arrays sub palette
 Select array constant and
drag onto block diagram
This creates an array shell
6 May 2015 61

Creating an Array on Block
Diagram
To finish creating the array
the data type the array
holds must be determined.
Drag a constant from a sub
palette into the elements
portion
 This determines the data
type of the array
6 May 2015 62
index elements
after dragging numeric constant
into elements

6 May 2015 63
Array expanded to show elements 0 through 10
Clicking on index array display other elements. The element on the far
left (or top) of the array has the index shown in the index box.
Light blue elements are elements that have not been initialized.
Array Constants on Block Diagram

Two dimensional array
6 May 2015 64

3-dimensional Array
6 May 2015 65
Index (0,0,3)

6 May 2015 66
Creating Arrays Via the Front Panel
 Arrays can also be created via the
front panel
 Click on the Array and Cluster sub
palette
 click and drag an array to the
front panel and this creates an
array control shell

6 May 2015 67
Creating Arrays Via the Front Panel
 A data type must be added to the
array shell
 drag a control or indicator of the
data type you want into the shell
Can change from double to int by
right clicking on elements and
selecting “data range”
click on icon under
“representation” and change to an
integer type
array shell

6 May 2015 68
Array Functions
 Build an array
Size an array
Form an array from a cluster or a cluster into
an array
Index an array
Find the max an min of an array
Insert and delete from an array or reshape
Sort a lD array
Convert an array to matrix, or a matrix to
array

Build and sizing an array
Complies multiple arrays or appends
elements to an n-dimensional array.
 Sizing an array just shows the
number of elements in the array on
the front panel.

Index Array
 Returns the element or sub-array of n-
dimension array at index.
When you wire an array to this function,
the function resizes automatically to display
index inputs for each dimension in the
array you wire to n-dimension array.
You also can add additional element or sub-
array terminals by resizing it.

Max and Min of an Array
 Returns the maximum and minimum values
found in array, along with the indexes for each
value. The array can be an n-dimensional array
of any type.
 Max/min index(es) is the index for the first
max/min value. If array is multidimensional,
max/min index(es) is an array whose elements
are the indexes for the first maximum/min
value in array.
 Would be good to use if you needed to know
when a graph peaked or lowest value

Sorting an Array
 Returns a sorted version of array with the
elements arranged in ascending order.
 If array is an array of clusters, the function
sorts the elements by comparing the first
elements.
 If the first elements match, the function
compares the second and subsequent elements.

Converting an Array to a Matrix
Converts an array to a matrix of
elements of the same type as the array
elements .
Can make each of the following
* to real matrix
* to column vector
* to complex matrix
* to complex column vector

Array => cluster or cluster =>array
Bundles each component input into a cluster
and assembles all component clusters into an
array of clusters. Each cluster contains a
single component. Input components must
be of the same type as the value wired to the
topmost component terminal.
Array to cluster converts a 1D array to a
cluster of elements of the same type as the
array elements.

Visual Programming Arrays in LabVIEW 75
Auto indexing
LabVIEW has a feature with loops
and arrays called auto indexing.
If you wish to carry out an operation
on every element of an array a loop is
required.
Assume we have an array and we
want to double every element.

Using Auto indexing
Array Indicator

Notes on Previous slide
No value wired to count terminal
 Count based on length of array
 Thick wire going in and coming out,
but thin inside the loop
◦ working with a single element of the
array
Must create array indicator to show
array when finished
◦ can be a bit tricky

Manipulating Arrays
Many functions for
working with arrays
initialize array
initial value
for all elements
size of the array

Getting the Length of an Array
array input
output is size
of array

Changing Values of Elements
Giving an array, set the value at position
2 (actually the 3rd element of the array)
to 1 more than its previous value
Uses Index Array and Replace Array
Subset
Index Array
array
index
value at element
Replace Array
Subset
array
index
new value for
element
resulting
array

Clusters
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Data structure that groups data together.
Data may be of different types.
Analogous to struct in C or a record in Pascal.
Elements must be either all controls or all
indicators.
Thought of as wires bundled into a cable.

Clusters Controls and Indicators
6 May 2015 82
1. Select a Cluster shell from
the Array & Cluster
subpalette
2. Place objects inside the shell

Building a Cluster
Clusters are built by bundling up a
collection of inputs and they are
complied into a cluster which can
then be manipulated to your liking.
They are perfect for organization and
complying data in a neat and uniform
way that is easily represented in the
front panel.

Bundling and Unbundling
 Assembles a cluster from individual elements.
 It can also be use to change the values of
individual elements in an existing cluster without
having to specify new values for all elements. To
do so, wire the cluster you want to change to the
middle cluster terminal of this function. When you
wire a cluster to this function, the function resizes
automatically to display inputs for each element in
the cluster. Also when you wire to the middle
terminal, all other inputs are optional.

Indexing A Cluster
Indexes a set of arrays and creates a
cluster array in which matches the
value of each element to a
corresponding location.

86
Cluster Order
 Elements have a logical order (start with 0).
 To change order, right-click the border and select
Reorder Controls in Cluster...

87
Using Clusters to Pass Data
to SubVIs
 Use clusters to pass
several values to one
terminal
Overcomes 28-terminal
limit
Simplifies wiring

88
Cluster Functions - Bundle
BundleBundle
ByNameCreate new cluster Modify existing cluster
Must have an existing
cluster to use this
function.

89
Cluster Functions - Unbundle
Unbundle Unbundle By Name

90
Error Cluster
Use the error in and error out clusters in each VI
you use or build to handle errors in the VI.
 The error clusters located on the
Controls»Array & Cluster palette include the
components of information shown.

91
Error Cluster Details
 Status is a Boolean value that
reports TRUE if an error occurred.
Most VIs, functions, and structures
that accept Boolean data also
recognize this parameter.
 Code is a signed 32-bit integer that
identifies the error numerically. A
non-zero error code coupled with a
status of FALSE signals a warning
rather than a fatal error.
 Source is a string that identifies
where the error occurred.

92
Error Handling with Clusters
 LabVIEW does not handle errors automatically.
In LabVIEW, you can make these error handling
decisions on the block diagram of the VI.
 Error handling in LabVIEW follows the dataflow
model. Just as data flow through a VI, so can
error information.
 Wire the error information from the beginning of
the VI to the end.
Error Cluster

Plotting Data
6 May 2015 93
Waveform Charts
Waveform and X-Y Graphs
Intensity Graphs

94
Waveform Charts
Selected from the Controls»Graphs and Charts palette

95
Wiring to Charts
Single-Plot Chart
Multiple-Plot Chart

96
Modifying Chart Properties
•Change the
appearance
•Set the format
and precision of
the axis
•Choose the plot
type
•Edit the scales
•Document the
chart

97
Customizing Charts and
GraphsRight-click and select Visible Items to view the
following items:
 Plot Legend
 Digital Display
 Scrollbar
 X and Y Scale
 Graph Palette
 Scale Legend
Graph Palette
Scale
Legend
Zoom
Subpalette

98
• Selected from the Graph subpalette
• Waveform Graph – Plot an array of numbers
against their indices
• XY Graph – Plot one array against another
Plot Legend
(point and line
styles)
Graph PaletteScale Legend
Graphs

99
Uniform X axis
Initial X = 0.0
Delta X = 1.0
Uniform X axis
you specify point
spacing
Single-Plot Waveform Graphs

100
Multiple-Plot Waveform Graphs
Each row is a
separate plot:
Initial X = 0
Delta X = 1
Each row is a
separate plot:
Bundle specifies
point spacing of the
X axis

101
• Non-uniform X axis
• Separate X and Y arrays
define data points
XY Graphs

102
Intensity Plots and Graphs
 Useful in displaying terrain, temperature patterns,
spectrum analysis, and image processing
 Data type is a 2D array of numbers; each number
represents a color
 Use these options to set and display color mapping
scheme
 Cursor also adds a third dimension

103
•The waveform chart is a special numeric indicator
that displays one or more plots. The waveform
chart has the following three update modes:
–A strip chart shows running data continuously scrolling from left
to right across the chart.
–A scope chart shows one item of data, such as a pulse or wave,
scrolling partway across the chart from left to the right.
–A sweep works similarly to a scope except it shows the old data on
the right and the new data on the left separated by a vertical line.
•Waveform graphs and XY graphs display data
from arrays.
•Right-click a waveform chart or graph or its
components to set attributes of the chart and its
plots.
Summary

6 May 2015 104
Structures
 Structures are graphical representations of the
loops and case statements of text based
programming languages.
 In text based programs, this can be accomplished
with statements like if else, case and so on.
 Decision making with the select function.

105
Simple Decision: Select Function
 If Temp Scale is TRUE, pass top input;
if temp scale is FALSE, pass bottom input.
 If the decision to be made is more complex than
a Select function can execute, a Case Structure
may be what is required.

6 May 2015 106
Structures…..
For Loop
While Loop
Case Structure
Sequence structure
Event Structure
Timed Structure

6 May 2015 107
Case Structure
 Contains multiple sub diagrams, only one of
which executes depending on the input value
passed to the structure.
Boolean Case Structure Example:
If Temp Scale is TRUE, execute True case;
if temp scale is FALSE, execute False case.

108
Boolean and Numeric Cases
Wire all possible outputs of the case structure

109
String Case
 String input. Like the numeric input case, the value of the
string
 determines which box to execute. Stress that the value much
match exactly or
 the structure will execute the default case.

Sequence Structure
Flat Sequence Structure: It displays all the
frames at once and executes the frames from left to
right and when all the data values wired to a frame
are available, until the last frame executes.
6 May 2015 110

Contd…
Stacked Sequence Structure: It stacks each frame so
you see only one frame at a time and executes
frame 0, then frame 1,and so on until the last frame
executes.
6 May 2015 111
 It can easily convert one into the other by selecting from its
pop-up menu, Replace with Stacked Sequence (to convert
from Flat to Stacked) or Replace>>Replace with Flat Sequence
(to convert from Stacked to Flat).

Event Structure
 It waits until an event happens and then
executes the appropriate case to handle that
event.
6 May 2015 112

Contd…
6 May 2015 113
 An event is an action that triggers a change
in state
User initiated
Button press
Mouse click
OS initiated
timeout
Software initiated
Message from another program
Variable reaches a specific value

Formula Node
 In the Structures sub-palette .
 Implement complicated equations.
 Variables created at border.
 Variable names are case sensitive.
 Each statement must terminate with a semicolon (;)
 Context Help Window shows available functions.
6 May 2015 114

115
Decision Making with Formula Nodes
Two different ways of using an if-then statement in a Formula Node.
Both structures produce the same result.

6 May 2015 116
String and File I/O
TOPICS:
How to create string controls and indicators
How to use several String functions
About file I/O operations
How to use the high-level File I/O VIs
How to use the low-level File I/O VIs
How to format text files for use in spreadsheets

6 May 2015 117
Strings
A string is a sequence of displayable or non-displayable (ASCII)
characters.
 Strings often are used to send commands to instruments, to
supply information about a test (such as operator name and
date), or to display results to the user.
Applications:
 Creating simple text messages.
Passing numeric data as character strings to instruments and converting
the strings to numeric values.
 Storing numeric data to disk. To store numeric data in an ASCII file,you
must convert numeric data to strings before writing the data to a disk
file.

6 May 2015 118
Creating String Controls and
Indicators
 String control/indicator is in the Controls»String
subpalette.
Normal display code display
Hex display
Password Display

119
Concatenate Strings
String Length
String Functions

120
String Functions
String Subset
Match Pattern

121
Converting Numerics to Strings:
Build String

122
Converting Strings to Numerics:
Scan From String

6 May 2015 123
Formatting Strings
 Array to Spreadsheet String
 Spreadsheet String To Array
 Scan from string
 Format into string
 Format value
 Scan value
 Scan from File
 Format into file

6 May 2015 124
File Input and Output ( I/O)
Four Hierarchy Levels:
High-level File VIs
Intermediate File VIs and
Functions
Advanced File Functions
sub-palette
Express VIs

125
• Write to Spreadsheet File
• Read from Spreadsheet File
• Write Characters to File
• Read Characters from File
• Read Lines from File
High-level File I/O VIs

126
Write to File Example
• Open/Create/Replace opens the existing file TEST1.DAT
and generates refnum and error cluster
• Write File writes the data
• Close File closes the file
• Simple Error Handler checks for errors.

127
Reading Data from a File
•Open/Create/Replace opens the file
•Read File reads the specified number of bytes from the file
•Close File closes the file
•Simple Error Handler checks for errors

128
Formatting a Spreadsheet String
• Spreadsheets are popular tools for data handling and
analysis
• There are many formats for spreadsheet data. One of the
most popular is tab-delimited:
– Columns are separated by a tab character
– Rows are separated by an end-of-line
character
Tab End of Line
A spreadsheet yields:

129
Creating a Spreadsheet File
Can replace Format Into String
and
Write File with Format Into File
in above example

130
Write LabVIEW Measurement File
 Includes the open, write, close and error
handling functions
 Handles formatting the string with either a tab
or comma delimiter
 Merge Signals function is used to combine data
into the dynamic data type

 About plug-in data acquisition (DAQ)
boards.
 About the organization of the DAQ VIs.
 How to acquire and display an analog
signal.
 How to perform a timed data acquisition.
 How to acquire data from multiple analog
channels.
 How to drive the digital I/O lines, and the
basics of buffered data acquisition.
DAQ Scope

133
Overview and Configuration
Fundamental task of a DAQ
system is to measure or generate
real-world physical signals
DAQ system consists of:
•Transducers
•Signal Conditioning
•Plug-in DAQ device
•Driver
•Software

 DAQ boards:
Analog I/O
Digital I/O
Counter/timer I/O
 DAQ library supports all DAQ boards
 LabVIEW uses the NI-DAQ driver-level software
Data Acquisition System Components
PLUG-IN DAQ BOARD: Measures (acquires),
processes, stores, and generates signals, as instructed
by software program. Examples: Analog and digital
signals’ input and output, counters, timers, etc.
COMPUTER with SOFTWARE: Control the DAQ board,
process, store, and display data, as instructed by software
program. Examples: LabVIEW application programs to acquire
data, simulate instruments, and generate results, etc.
SIGNAL CONDITIONING: Modify transducer signals
to match DAQ board specs/ranges. Examples: amplification
or attenuation, filtering, excitation, etc.
TRANSDUCERS: Sense the measured quantities
and change their properties or generate corresponding
electrical signals. Examples: strain gage, thermocouple,
accelerometer, potentiometer, etc.
Data Acquisition - DAQ

Transducers
Sense Phenomena
Produce Electrical Signal
Examples:
 Thermocouples, Thermistors
 Strain Gauges, RTDs
 Pressure Transducers, Load Cells
 Accellerometers, Microphones
 Potentiometers, Etc..

Signal Conditioning
Condition Transducer Signals
Make Signal Suitable for DAQ Board
Examples:
 Amplification/Attenuation
 Linearization/Calibration
 Filtering
 Multiplexing (up to 3,072 channels)
 Isolation, Excitations, Etc.

DAQ Hardware & Software
Configurations
Hardware:
 Setting DIP Switches and Jumpers for Particular
Options/Applications
 Newer and Plug-and-Play Boards are Software
Configured
 Cabling, Signal Conditioning, Terminal Blocks, etc.
Software:
 Set-up and Configuration Programs
 Drivers: Interface between DAQ Board and Computer
 DAQ Application Software (LabVIEW, C, Basic, etc.)
 Data Acquisition
 Data Analysis (Statistics, FFT, DSP, etc.)
 Data Presentation (Graphing, Plotting, Tabulation, etc.)

138
DAQ Hardware Configuration
Measurement & Automation Explorer (MAX)

139
Channels and Tasks
Signals
ai 0
ai 1
ai 2
Sine Wave 1
Sine Wave 2
Sine Wave 3
Channel names
Tasks
Timing and Triggering

141
Data Acquisition in LabVIEW
Traditional NI-DAQ
Specific VIs for
performing:
• Analog Input
• Analog Output
• Digital I/O
• Counter operations
NI-DAQmx
Next generation driver:
• VIs for performing a
task
• One set of VIs for all
measurement types

142
NI-DAQmx Data Acquisition
Single set of VIs used to perform
analog I/O, digital I/O, and counter
operations
DAQ Assistant Express VI
• Quickly and easily program the DAQ
device
• Creates a local task
• Most applications can use the DAQ
Assistant Express VI

143
NI-DAQmx Data Acquisition
Task Types
Measurement
type
can be:
•Analog Input
•Analog Output
•Counter Input
•Counter Output
•Digital I/O

144
Analog Input
Analog Input
task is
specific to the
measurement

Analog Input Considerations
• Single-Ended vs. Differential
• Resolution
• Range
• Sampling Rate / Aliasing
• Averaging / Noise reduction
10
1 * 212
= 2.4 mV
20
1 * 212
= 4.8 mV
Adequately sampled
Aliased due to undersampling
8
3-bit ADC 16-bit ADC
Time
.
10 V range
12 bit
resolution
1X Gain
Aliasing
.

146
Analog Input Task Timing and
Triggering
Configures the number of samples
and sample rate for the task
Configures the start and reference
triggers for the task

147
Data Logging
 It is often necessary to permanently store data
that is acquired from the DAQ device
 LabVIEW includes the ability to read and write
a LabVIEW Measurement File
 LabVIEW Measurement File is an ASCII text
file

148
Analog Output
Analog Output
task is specific
to the
generation type

149
Analog Output Task Timing and
Triggering
Configures the number of
samples and sample rate for
the task
Configures the start and
reference triggers for the task

HOW do I make a DAQ device
provide a voltage???

 The BASICS: You need 3 things…..
LabVIEW Application
MAX
DAQ Device

Voltage Output
Note the ANALOG side
of the USB devices near
your computers.
There should be terminals
labeled AO0 and AO1
AO stands for Analog
Output.
Most of the NI devices
have at least 2 such
terminals
For output we wire a
terminal and a ground.

Voltage Output
• We access the analog output functions via
LabVIEW. To do this we can access the DAQ
Assistant.
• We can right-mouse click and access
Functions on the Block Diagram.
• Select the DAQ Assistant on the OUTPUT
Menu

Voltage Output
• When the DAQ Assistant is selected you get 2 choices:
• “Acquire Signals”…what we have used so far
• “Generate Signals” choose this one for voltage output!

• Once you select Generate Signals choose Voltage
• The device or devices will appear. Choose either
one or both channels (depending on how many
signals must be generated.)

157
Counters
A counter is a digital timing
device
Typical uses of a counter:
• Event counting
• Frequency measurement
• Period measurement
• Position measurement
• Pulse generation
Gate
Source
Output
Count Register
Count register – Stores the current count of the counter
Source – Input that causes the counter to increment each time it toggles
Gate – Input that is used to enable or disable the function of the counter
Output – Signal that generates pulses or a series of pulses

158
Digital Input and Output
 Digital I/O
can read
from or write
to a line or an
entire digital
port
 A digital port
is a collection
of digital
lines

Analog Input and Output VIs
AI Sample Channel
AO Update Channel

Waveform Input and Output VIs
AI Acquire Waveform
AO Generate Waveform

Digital Input and Output
Write to Digital Line Read from Digital Line
Write to Digital Port Read from Digital Port

DAQ Summary
 Identify I/O Signal Types:
Transducers/Controllers
 Choose a Signal Conditioning Method
 Select a Data Acquisition (DAQ)
Device
 Choose Terminals/Cables for the
Hardware
 Select DAQ Software

Signal/Sampling Resolution
Sampling/Time Resolution (Speed)
Signal/MagnitudeResolution

Real measurements
of a simple sine-harmonic
How come this if the measured signal
is a simple sine-harmonic wave?

DEMO Application
 Sometimes we need more than just 5
or 10 volts
 How can the LabVIEW output
function help us to run a pump or
motor?
Application: We need to use LabVIEW
to control a motor. The motor uses a
variable voltage from 60 to 120 volts
to adjust from top speed to low speed.

Contd..
In this case we would use a device with
the motor’s manual control electronics.
The controller will accept a grounded DC
signal and generates a proportional
output voltage.
This output can be supplied to the speed
setting circuit of the motor’s controller.
This will drive the motor at a speed
proportional to the signal that LabVIEW
sends to it.

DEMO Application
Main power supplied
By 120 VAC outlet
Control box
With SCR-based
potentiometers
0-10 VDC “control” volts from
LabVIEW
Power line
from control
Drive Motor
Turn-Table with experiment

Fast Fourier Transform
6 May 2015 169
 It is a tool to connect between time domain
and frequency domain
 Any waveform in the time domain can be
represented by weighted sum of sines and
cosines.
The sum waveform appears in the frequency
domain as amplitude and phase values at
each component (fo,2fo,3fo)

Why we exchange between time
domain and frequency domain?
6 May 2015 170

Why Fourier Transform?
6 May 2015 171
This example is a sound record analysis. The left picture is the sound
signal changing with time. However, we have no any idea about this
sound by the time record. By the Fourier transform, we know that this
sound is generated at 50Hz and 120Hz mixed with other noises.

Contd…
6 May 2015 172
 It is used for analyzing and measuring
signals from plug in data acquisition
(DAQ) devices
It can measure the frequency components
within the signal.
FFT based measurements requires
digitization of a continues signal.
Acc to Nyquist Criteria ,the sampling
frequency Fs> 2Fm.if this criteria violated
a phenomenon k/s ALIASING.

Application
6 May 2015 176
Require fast response time such as
 Transient analysis,
Vibrations and
Shock Testing using FFT Analysis

Power Spectrum
6 May 2015 177
Calculate the harmonics power in a signal
The power spectrum Sxx(f) of a time
domain signal x(t) is defined as
Sxx(f) =X(f)X*(f)
=|X(f)2|
X*(f)=complex conjugate
 Power Spectrum is identical to the real part
of FFT.
It calculates the harmonic power in discrete
time real values sequence.

Virtual instrumentation (LabVIEW)

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