National Instruments LabVIEW Application Note

User Manual

LabVIEW User Manual

January 1998 Edition

Part Number 320999B-01

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© Copyright 1992, 1998 National Instruments Corporation. All rights reserved.

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Contents

About This Manual

Organization of This Manual................................................ ...... .....................................xxiii

Part I, Introduction to G Programming..............................................................xxiii

Part II, I/O Interfaces.........................................................................................xxiv

Part III, Analysis................................................................................................xxiv

Part IV, Network and Interapplication Communication....................................xxv

Part V, Advanced G Programming....................................................................xxvi

Appendices, Glossary, and Index......................................................................xxvi

Conventions Used in This Manual...................................................................................xxvii

Related Documentation....................................................................................................xxviii

Customer Communication...............................................................................................xxviii

Chapter 1
Introduction

What Is LabVIEW? .........................................................................................................1-1

How Does LabVIEW Work?................................................ ...... ..... ................................1-1

G Programming.................................................................................................1-2

Organization of the LabVIEW System (Windows).........................................................1-4

Startup Screen on Windows..............................................................................1-5

Organization of the LabVIEW System (Macintosh).......................................................1-6

Organization of the LabVIEW System (UNIX)..............................................................1-7

Toolkit Support................................................................................................................1-9

Where Should I Start?......................................................................................................1-9

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Introduction to G Programming

Chapter 2
Creating VIs

What is a Virtual Instrument?..........................................................................................2-1

How Do You Build a VI?................................................................................................2-1

VI Hierarchy..................................... ....................................... ..........................2-1

Controls, Constants, and Indicators...................................................................2-2

Terminals...........................................................................................................2-3

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Wires.................................................................................................................2-4

VI Documentation............................................................ ..... ...... ......................2-10

What is a SubVI?.............................................................................................................2-12

Hierarchy Window............................................................................................2-12

Icon and Connector...........................................................................................2-14

Opening, Operating, and Changing SubVIs......................................................2-19

Front Panel........................................................................................................2-19

Block Diagram..................................................................................................2-20

How Do You Debug a VI?.............................................................................................. 2-21

Chapter 3
Loops and Charts

What is a Structure?.........................................................................................................3-1

Charts...............................................................................................................................3-2

Chart Modes......................................................................................................3-2

Faster Chart Updates.........................................................................................3-3

Overlaid Versus Stacked Plots.......................................................................... 3-3

While Loops ....................................................................................................................3-4

Front Panel........................................................................................................3-5

Block Diagram..................................................................................................3-6

Mechanical Action of Boolean Switches..........................................................3-8

Timing...............................................................................................................3-10

Preventing Code Execution in the First Iteration..............................................3-12

Shift Registers .................................................................................................................3-13

Front Panel........................................................................................................3-15

Block Diagram..................................................................................................3-15

Using Uninitialized Shift Registers...................................................................3-17

Front Panel........................................................................................................3-19

Block Diagram..................................................................................................3-20

For Loops.........................................................................................................................3-22

Numeric Conversion.........................................................................................3-24

Front Panel........................................................................................................3-25

Block Diagram..................................................................................................3-26

Tip Strips ............................................................................................2-4

Wire Stretching...................................................................................2-5

Selecting and Deleting Wires.............................................................2-5

Bad Wires...........................................................................................2-6

Search Hierarchy ................................................................................2-14

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Chapter 4
Case and Sequence Structures and the Formula Node

Case Structure...................................................... ...... ...... ................................................4-2

Front Panel.........................................................................................................4-2

Block Diagram...................................................................................................4-3

VI Logic................................ ...... ....................................... ................................4-4

Sequence Structures.........................................................................................................4-5

Front Panel.........................................................................................................4-5

Modifying the Numeric Format..........................................................4-6

Setting the Data Range........................................................................4-7

Block Diagram...................................................................................................4-7

Formula Node.................................................................................................................. 4-11

Front Panel.........................................................................................................4-14

Block Diagram...................................................................................................4-14

Artificial Data Dependency.............................................................................................4-15

Chapter 5
Arrays, Clusters, and Graphs

Arrays...............................................................................................................................5-1

How Do You Create and Initialize Arrays? ......................................................5-1

Array Controls, Constants, and Indicators..........................................5-2

Auto-Indexing....................................................................................................5-2

Front Panel.........................................................................................................5-3

Block Diagram...................................................................................................5-4

Multiplot Graphs ...............................................................................................5-7

Using Auto-Indexing to Set the For Loop Count..............................................5-10

Using Array Functions ......................................................................................5-10

Build Array .........................................................................................5-10

Initialize Array....................................................................................5-11

Array Size ...........................................................................................5-12

Array Subset........................................................................................5-13

Index Array.........................................................................................5-14

Front Panel.........................................................................................................5-17

Block Diagram...................................................................................................5-18

Efficient Memory Usage: Minimizing Data Copies..........................................5-18

What is Polymorphism?...................................................................................................5-19

Clusters ............................................................................................................................ 5-20

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Graphs..............................................................................................................................5-20

Customizing Graphs..........................................................................................5-20

Data Acquisition Arrays....................................................................................5-22

Front Panel........................................................................................................5-22

Block Diagram..................................................................................................5-23

Intensity Plots..................................................................................................................5-25

Chapter 6
Strings and File I/O

Strings.............................................................................................................................. 6-1

Creating String Controls and Indicators............................................................6-1

Strings and File I/O........................................................................................... 6-2

Front Panel........................................................................................................6-2

Block Diagram..................................................................................................6-3

Front Panel........................................................................................................6-4

Block Diagram..................................................................................................6-4

Front Panel........................................................................................................6-7

Block Diagram..................................................................................................6-8

File I/O.............................................................................................................................6-9

File I/O Functions .............................................................................................6-9

Writing to a Spreadsheet File..........................................................................................6-11

Front Panel........................................................................................................6-12

Block Diagram..................................................................................................6-12

Front Panel........................................................................................................6-14

Block Diagram..................................................................................................6-15

Front Panel........................................................................................................6-16

Block Diagram..................................................................................................6-17

Using the File I/O Functions...........................................................................................6-18

Specifying a File ................................................... ..... ...... .................................6-18

Paths and Refnums............................................................................................ 6-19

File I/O Examples .............................................................................................6-19

Datalog Files....................................................................................................................6-20

Graph Cursors.....................................................................................5-21

Graph Axes.........................................................................................5-22

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I/O Interfaces

Chapter 7
Getting Started with a LabVIEW Instrument Driver

What is a LabVIEW Instrument Driver?.........................................................................7-1

Where Can I Get Instrument Drivers?.............................................................................7-2

Where Should I Install My LabVIEW Instrument Driver? .............................................7-2

How Do I Access the Instrument Driver VIs?.................................................................7-3

Instrument Driver Structure........................................................ .....................................7-4

Obtaining Help for Your Instrument Driver VIs .............................................................7-6

Running the Getting Started VI Interactively

(Selecting the GPIB Address, Serial Port, and Logical Address).................................7-7

Interactively Testing Component VIs..............................................................................7-8

Building Your Application ..............................................................................................7-9

Related Topics .................................................................................................................7-10

Open VISA Session Monitor VI........................................................................7-10

Error Handling...................................................................................................7-11

Testing Communication with Your Instrument.................................................7-11

Developing a Quick and Simple LabVIEW Instrument Driver.......................................7-12

Modifying an Existing Driver ...........................................................................7-12

Developing a Simple Driver..............................................................................7-13

Developing a Full-Featured Driver ...................................................................7-17

Using LabVIEW with IVI Instrument Drivers..................................................7-17

Contents

Chapter 8
LabVIEW VISA Tutorial

What is VISA?.................................................................................................................8-1

Supported Platforms and Environments............................................................ 8-1

Why Use VISA? ........................................................ ...... ..... ...........................................8-2

VISA Is the Standard.........................................................................................8-2

Interface Independence...................................... ....................................... .........8-2

Platform Independence......................................................................................8-2

Easily Adapted to the Future.............................................................................8-2

Basic VISA Concepts ......................................................................................................8-3

Default Resource Manager, Session, and Instrument Descriptors....................8-3

How Do I Search for Resources?......................................................................8-4

What is a VISA Class?......................................................................................8-5

Popping Up on a VISA Control..........................................................8-6

Opening a Session ............................................. ..... ........................................ ...8-6

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How Do the Default Resource Manager, Instrument Descriptors,

and Sessions Relate?......................................................................................8-7

Closing a Session..............................................................................................8-8

When Is It a Good Idea to Leave a Session Open?.............................8-8

Error Handling with VISA................................................................................8-9

Easy VISA VIs.................................. ..... ...... ...... ....................................... ......................8-11

Message-Based Communication.....................................................................................8-11

How Do I Write To and Read From a Message-Based Device?......................8-12

Register-Based Communication (VXI only)...................................................................8-12

Basic Register Access.......................................................................................8-14

Basic Register Move.........................................................................................8-15

Low-Level Access Functions............................................................................8-15

Using VISA to Perform Low-Level Register Accesses ..................... 8-15

Bus Errors........................................................................................... 8-17

Comparison of High-Level and Low-Level Access ......................................... 8-17

Speed .................................................................................................. 8-17

Ease of Use.........................................................................................8-18

Accessing Multiple Address Spaces...................................................8-18

VISA Properties...............................................................................................................8-18

Serial .................................................................................................................8-20

GPIB.................................................................................................................. 8-21

VXI....................................................................................................................8-21

VISA Property Examples..................................................................................8-22

Serial Write and Read.........................................................................8-22

How Do I Set a Termination Character for a Read Operation?.......... 8-22

VXI Properties.................................................................................... 8-23

Events..............................................................................................................................8-24

GPIB SRQ Events.............................................................................................8-24

Trigger Events...................................................................................................8-25

Interrupt Events.................................................................................................8-25

Locking............................................................................................................................8-26

Shared Locking.................................................................................................8-28

Platform-Specific Issues..................................................................................................8-28

Programming Considerations............................................................................8-29

Multiple Applications Using the NI-VISA Driver............................. 8-29

Multiple Interface Support Issues.....................................................................8-29

VXI and GPIB Platforms....................................................................8-29

Multiple GPIB-VXI Support .................................. ...... ...... ................8-30

Serial Port Support..............................................................................8-30

VME Support...................................................................................... 8-30

Debugging A VISA Program..........................................................................................8-31

Debugging Tool for Windows 95/NT...............................................................8-32

VISAIC............................................................................................................................8-32

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Chapter 9
Introduction to LabVIEW GPIB Functions

Types of Messages...........................................................................................................9-1

The Controller-In-Charge and System Controller...........................................................9-3

Compatible GPIB Hardware............................................................................................9-3

LabVIEW for Windows 95 and Windows 95-Japanese....................................9-3

LabVIEW for Windows NT............. ..... ...... ....................................... ...............9-3

LabVIEW for Windows 3.1 .................................................... ..........................9-4

LabVIEW for Mac OS....................................... ..... ........................................ ...9-4

LabVIEW for HP-UX.................................................................... ....................9-4

LabVIEW for Sun............................. ....................................... ..........................9-5

LabVIEW for Concurrent PowerMAX........................ .....................................9-5

Chapter 10
Serial Port VIs

Handshaking Modes ........................................................................................................10-2

Software Handshaking—XON/XOFF...............................................................10-2

Error Codes......................................................................................................................10-2

Port Number.................................................... ..... ........................................ ....................10-3

Windows 95 and 3.x..........................................................................................10-3

Macintosh..........................................................................................................10-3

UNIX.................................................................................................................10-3

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Analysis

Chapter 11
Introduction to Analysis in LabVIEW

The Importance of Data Analysis....................................................................................11-1

Full Development System................................................................................................11-3

Analysis VI Overview .....................................................................................................11-3

Notation and Naming Conventions..................................................................................11-6

Data Sampling.................................................................................................................. 11-9

Sampling Signals...............................................................................................11-9

Sampling Considerations...................................................................................11-10

Why Do You Need Anti-Aliasing Filters?........................................................11-13

Why Use Decibels? ................................................ ...........................................11-14

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Chapter 12
Signal Generation

Normalized Frequency....................................................................................................12-1

Front Panel........................................................................................................12-5

Block Diagram..................................................................................................12-6

Wave and Pattern VIs......................................................................................................12-7

Phase Control.................................................................................................... 12-7

Front Panel........................................................................................................12-8

Block Diagram..................................................................................................12-9

Front Panel........................................................................................................12-11

Block Diagram..................................................................................................12-12

Chapter 13
Digital Signal Processing

The Fast Fourier Transform (FFT)..................................................................................13-1

DFT Calculation Example ................................................................................13-2

Magnitude and Phase Information....................................................................13-4

Frequency Spacing between DFT/FFT Samples.............................................................13-5

Fast Fourier Transforms....................................................................................13-7

Zero Padding.....................................................................................................13-8

FFT VIs in the Analysis Library.......................................................................13-9

Front Panel........................................................................................................13-10

Block Diagram..................................................................................................13-11

Two-Sided FFT.................................................................................................13-12

One-Sided FFT..................................................................................................13-12

The Power Spectrum .......................................................................................................13-14

Loss of Phase Information................................................................................13-14

Frequency Spacing between Samples...............................................................13-14

Summary..........................................................................................................................13-15

Chapter 14
Smoothing Windows

Introduction to Smoothing Windows..............................................................................14-1

About Spectral Leakage and Smoothing Windows.........................................................14-2

Windowing Applications.................................................................................................14-7

Characteristics of Different Types of Window Functions...............................................14-7

Rectangular (None)...........................................................................................14-7

Hanning.............................................................................................................14-8

Hamming...........................................................................................................14-9

Kaiser-Bessel ....................................................................................................14-10

Triangle.............................................................................................................14-11

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Flattop................................................................................................................14-11

Exponential........................................................................................................14-12

Windows for Spectral Analysis Versus Windows for Coefficient Design......................14-13

What Type of Window Do I Use?.....................................................................14-16

Front Panel.........................................................................................................14-17

Block Diagram...................................................................................................14-18

Chapter 15
Spectrum Analysis and Measurement

Introduction to Measurement VIs....................................................................................15-1

You Will Learn................................................................................................................15-4

Spectrum Analysis...........................................................................................................15-4

Calculating the Amplitude and Phase Spectrum of a Signal.............................15-4

Front Panel.........................................................................................................15-5

Block Diagram...................................................................................................15-6

Calculating the Frequency Response of a System.............................................15-7

Front Panel.........................................................................................................15-8

Block Diagram...................................................................................................15-9

Harmonic Distortion........................................................................................................15-10

Total Harmonic Distortion ................................................................................15-11

Using the Harmonic Analyzer VI......................................................................15-12

Block Diagram...................................................................................................15-14

Front Panel.........................................................................................................15-15

Summary..........................................................................................................................15-16

Contents

Chapter 16
Filtering

Introduction to Digital Filtering Functions ......................................................................16-1

Ideal Filters ......................................................................................................................16-3

Practical (Nonideal) Filters..............................................................................................16-4

The Transition Band.......................................................................................... 16-4

Passband Ripple and Stopband Attenuation......................................................16-5

IIR and FIR Filters...........................................................................................................16-6

Filter Coefficients..............................................................................................16-8

Infinite Impulse Response Filters....................................................................................16-8

Cascade Form IIR Filtering...............................................................................16-10

Butterworth Filters.............................................................................................16-12

Chebyshev Filters..............................................................................................16-12

Chebyshev II or Inverse Chebyshev Filters.......................................................16-13

Elliptic (or Cauer) Filters...................................................................................16-14

Bessel Filters .....................................................................................................16-15

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Finite Impulse Response Filters......................................................................................16-16

Nonlinear Filters..............................................................................................................16-20

How Do I Decide Which Filter to Use?..........................................................................16-20

Summary..........................................................................................................................16-24

Chapter 17
Curve Fitting

Introduction to Curve Fitting...........................................................................................17-1

General LS Linear Fit Theory.........................................................................................17-6

How to Use the General LS Linear Fit VI........................................... ............................17-11

Nonlinear Lev-Mar Fit Theory........................................................................................17-18

Using the Nonlinear Lev-Mar Fit VI...............................................................................17-19

Designing FIR Filters by Windowing...............................................................16-17

Designing Optimum FIR Filters Using the Parks-McClellan Algorithm.........16-18

Designing Narrowband FIR Filters...................................................................16-18

Windowed FIR Filters....................................................................................... 16-19

Optimum FIR Filters.........................................................................................16-19

FIR Narrowband Filters....................................................................................16-19

Front Panel........................................................................................................16-22

Block Diagram..................................................................................................16-23

Applications of Curve Fitting ...........................................................................17-3

Front Panel........................................................................................................17-4

Block Diagram..................................................................................................17-5

Building the Observation Matrix......................................................................17-15

Front Panel........................................................................................................17-21

Block Diagram..................................................................................................17-22

Chapter 18
Linear Algebra

Linear Systems and Matrix Analysis...............................................................................18-1

Types of Matrices..............................................................................................18-1

Determinant of a Matrix....................................................................................18-2

Transpose of a Matrix.......................................................................................18-3

Can You Obtain One Vector as a Linear Combination

of Other Vectors? (Linear Independence).......................................18-3

How Can You Determine Linear Independence? (Matrix Rank).......18-4

“Magnitude” (Norms) of Matrices....................................................................18-5

Determining Singularity (Condition Number)..................................................18-7

Basic Matrix Operations and Eigenvalues-Eigenvector Problems..................................18-9

Dot Product and Outer Product............................................. ...... ......................18-10

Eigenvalues and Eigenvectors ..........................................................................18-12

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Matrix Inverse and Solving Systems of Linear Equations ..............................................18-14

Solutions of Systems of Linear Equations.........................................................18-15

Front Panel.........................................................................................................18-17

Block Diagram...................................................................................................18-18

Matrix Factorization ........................................................................................................18-20

Pseudoinverse....................................................................................................18-21

Summary..........................................................................................................................18-21

Chapter 19
Probability and Statistics

Probability and Statistics .................................................................................................19-1

Statistics...........................................................................................................................19-3

Mean..................................................................................................................19-3

Median...............................................................................................................19-3

Sample Variance.......................................... ...... ..... ........................................ ...19-4

Standard Deviation............................................................................................19-5

Mode..................................................................................................................19-6

Moment About Mean ........................................................................................19-6

Histogram..........................................................................................................19-7

Mean Square Error (MSE).................................................................................19-10

Root Mean Square (RMS).................................................................................19-11

Probability........................................................................................................................19-12

Random Variables.............................................................................................19-12

Normal Distribution...........................................................................................19-15

Front Panel.........................................................................................................19-17

Block Diagram...................................................................................................19-18

Summary..........................................................................................................................19-20

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Network and Interapplication Communication

Chapter 20
Introduction to Communication

LabVIEW Communication Overview............................. ..... ........................................ ...20-1

Introduction to Communication Protocols.......................................................................20-1

File Sharing Versus Communication Protocols...............................................................20-2

Client/Server Model.........................................................................................................20-3

A General Model for a Client............................................................................20-3

A General Model for a Server...........................................................................20-4

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Chapter 21
TCP and UDP

Overview .........................................................................................................................21-1

Internet Protocol (IP) .......................................................................................................21-2

User Datagram Protocol (UDP).......................................................................................21-3

Transmission Control Protocol (TCP).............................................................................21-4

LabVIEW and TCP/IP .................................... ..................................................21-2

Internet Addresses............................................................................................. 21-2

Using UDP........................................................................................................21-3

Using TCP.........................................................................................................21-4

TCP Versus UDP................................................................................21-5

TCP Client Example...........................................................................21-5

Timeouts and Errors ...........................................................................21-6

TCP Server Example..........................................................................21-6

TCP Server with Multiple Connections..............................................21-7

Setup..................................................................................................................21-7

UNIX ..................................................................................................21-7

Macintosh ...........................................................................................21-8

Windows 3.x.......................................................................................21-8

Windows 95 and Windows NT ..........................................................21-8

Chapter 22
ActiveX Support

ActiveX Automation Server Functionality......................................................................22-2

ActiveX Server Properties and Methods.........................................................................22-3

ActiveX Automation Client Functionality...................................................................... 22-3

ActiveX Client Examples................................................................................................22-4

Converting ActiveX Variant Data to G Data....................................................22-4

Adding a Workbook to Microsoft Excel from LabVIEW ................................22-5

Chapter 23
Using DDE

DDE Overview................................................................................................................23-1

Services, Topics, and Data Items......................................................................23-2

Examples of Client Communication with Excel...............................................23-2

LabVIEW VIs as DDE Servers.........................................................................23-4

Requesting Data Versus Advising Data................................ ...... ...... ................23-6

Synchronization of Data......................................................................... ...........23-7

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Networked DDE................................................................................................23-8

Using NetDDE....................................................................................23-10

Server Machine.....................................................................23-10

Client Machine .....................................................................23-12

Chapter 24
AppleEvents

AppleEvents .....................................................................................................................24-1

Sending AppleEvents........................................................................................24-2

Client Server Model ..........................................................................................24-2

AppleEvent Client Examples ............................................................................24-3

Launching Other Applications............................................................24-3

Sending Events to Other Applications................................................24-3

Dynamically Loading and Running a VI............................................24-4

Chapter 25
Program-to-Program Communication

Introduction to PPC .........................................................................................................25-1

Ports, Target IDs, and Sessions.........................................................................25-2

PPC Client Example..........................................................................................25-3

PPC Server Example .........................................................................................25-4

PPC Server with Multiple Connections.............................................................25-5

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Advanced G Programming

Chapter 26
Customizing VIs

How Do You Customize a VI?........................................................................................26-1

Set Window Options..........................................................................................26-1

SubVI Node Setup.............................................................................................26-2

Front Panel.........................................................................................................26-2

Block Diagram...................................................................................................26-3

Front Panel.........................................................................................................26-6

Block Diagram...................................................................................................26-7

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Chapter 27
Front Panel Object Attributes

Front Panel........................................................................................................27-3

Block Diagram..................................................................................................27-3

Chapter 28
Program Design

Use Top-Down Design....................................................................................................28-1

Make a List of User Requirements ...................................................................28-1

Design the VI Hierarchy...................................................................................28-1

Create the Program............................................................................................28-3

Plan Ahead with Connector Panes .................................................................................. 28-3

SubVIs with Required Inputs........................................... ..... ............................28-4

Good Diagram Style........................................................................................................28-4

Watch for Common Operations........................................................................28-5

Use Left-to-Right Layouts................................................................................28-5

Check for Errors................................................................................................28-6

Watch Out for Missing Dependencies..............................................................28-7

Avoid Overuse of Sequence Structures............................................................28-8

Study the Examples...........................................................................................28-9

Chapter 29
Where to Go from Here

Other Useful Resources...................................................................................................29-1

Solution Wizard and Search Examples............................................................. 29-1

Data Acquisition Applications..........................................................................29-1

G Programming Techniques.............................................................................29-1

Function and VI Reference...............................................................................29-2

Resources for Advanced Topics......................................................................................29-2

Attribute Nodes.................................................................................................29-2

VI Setup and Preferences..................................................................................29-2

Local and Global Variables...............................................................................29-3

Creating SubVIs........................................ ........................................ ................29-3

VI Profiles....................................................... ...... ....................................... .....29-3

Control Editor ...................................................................................................29-4

List and Ring Controls......................................................................................29-4

Call Library Function.................................................................. ......................29-4

Code Interface Nodes............................................................ ...... ......................29-4

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Appendices, Glossary, and Index

Appendix A
Analysis References

Appendix B
Common Questions

Appendix C
Customer Communication

Glossary

Index

Figures, Tables, and Activities

Figures

Figure 11-1. Analog Signal and Corresponding Sampled Version..............................11-9

Figure 11-2. Aliasing Effects of an Improper Sampling Rate.....................................11-10

Figure 11-3. Actual Signal Frequency Components....................................................11-11

Figure 11-4. Signal Frequency Components and Aliases............................................11-12

Figure 11-5. Effects of Sampling at Different Rates....................................................11-13

Contents

Figure 14-1. Periodic Waveform Created from Sampled Period.................................14-2

Figure 14-2. Sine Wave and Corresponding Fourier Transform .................................14-3

Figure 14-3. Spectral Representation When Sampling a Nonintegral Number

of Samples............................................................................................14-4

Figure 14-4. Time Signal Windowed Using a Hamming Window..............................14-6

Figure 22-1. Preferences Dialog Box, Server Configuration.......................................22-2

Figure 22-2. Block Diagram Displaying ActiveX Variant Data to G Data.................22-4

Figure 22-3. Adding a Workbook to Microsoft Excel.................................................22-5

Figure 25-1. PPC VI Execution Order (Used by Permission

of Apple Computer, Inc.)......................................................................25-5

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Contents

Tables

Table 22-1. Functions for ActiveX Automation Client Support................................ 22-3

Table 23-1. Values to Add in Place of Default..........................................................23-11

Activities

Activity 2-1. Create a VI..............................................................................................2-7

Activity 2-2. Document a VI........................................................................................2-10

Activity 2-3. Create an Icon and Connector.................................................................2-17

Activity 2-4. Call a SubVI............................................................................................2-19

Activity 2-5. Debug a VI in LabVIEW........................................................................2-22

Activity 3-1. Experiment with Chart Modes................................................................3-3

Activity 3-2. Use a While Loop and a Chart................................................................3-5

Activity 3-3. Change the Mechanical Action of a Boolean Switch.............................3-9

Activity 3-4. Control Loop Timing..............................................................................3-10

Activity 3-5. Use a Shift Register ................................................................................3-15

Activity 3-6. Create a Multiplot Chart .........................................................................3-19

Activity 3-7. Use a For Loop........................................................................................3-25

Activity 4-1. Use the Case Structure............................................................................4-2

Activity 4-2. Use a Sequence Structure........................................................................ 4-5

Activity 4-3. Use the Formula Node............................................................................4-13

Activity 5-1. Create an Array with Auto-Indexing ......................................................5-3

Activity 5-2. Use Auto-Indexing on Input Arrays .......................................................5-8

Activity 5-3. Use the Build Array Function.................................................................5-17

Activity 5-4. Use the Graph and Analysis VIs.............................................................5-22

Activity 6-1. Concatenate a String...............................................................................6-2

Activity 6-2. Use Format Strings .................................................................................6-4

Activity 6-3. String Subsets and Number Extraction...................................................6-7

Activity 6-4. Write to a Spreadsheet File.....................................................................6-12

Activity 6-5. Append Data to a File.............................................................................6-14

Activity 6-6. Read Data from a File.............................................................................6-16

Activity 12-1. Learn More about Normalized Frequency..............................................12-5

Activity 12-2. Use the Sine Wave and Sine Pattern VIs................................................12-8

Activity 12-3. Build a Function Generator.....................................................................12-11

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Contents

Activity 13-1. Use the Real FFT VI ...............................................................................13-10

Activity 14-1. Compare a Windowed and Nonwindowed Signal ..................................14-17

Activity 15-1. Use the Amplitude and Phase Spectrum VI............................................15-5

Activity 15-2. Compute the Frequency and Impulse Response......................................15-8

Activity 15-3. Calculate Harmonic Distortion................................................................15-14

Activity 16-1. Extract a Sine Wave................................................................................16-22

Activity 17-1. Use the Curve Fitting VIs........................................................................17-4

Activity 17-2. Use the General LS Linear Fit VI ...........................................................17-14

Activity 17-3. Use the Nonlinear Lev-Mar Fit VI..........................................................17-20

Activity 18-1. Compute the Inverse of a Matrix.............................................................18-17

Activity 18-2. Solve a System of Linear Equations........................................................18-19

Activity 19-1. Use the Normal Distribution VI..............................................................19-17

Activity 26-1. Use Setup Options for a SubVI...............................................................26-2

Activity 27-1. Use an Attribute Node.............................................................................27-3

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National Instruments Corporation xxi LabVIEW User Manual

About This Manual

The LabVIEW User Manual provides information about creating virtual
instruments (VIs). This manual also includes information about the
interfaces to which you can input and output data, using LabVIEW VIs to
perform analysis operations, and how LabVIEW handles network and
interapplication communication. Please read the LabVIEW Release Notes
before you use the LabVIEW User Manual.

Organization of This Manual

The LabVIEW User Manual is organized as follows.

• Chapter 1, Introduction, introduces the unique LabVIEW approa ch to
programming. It also e xplains ho w to start us ing LabVIEW to de v elop
programs.

Part I, Introduction to G Programming

This section contains basic information ab out creating virtual instruments
(VIs), using VIs in other VIs, programming structures such as loops, and
data structures such as arrays and strings.

Part I, Introduction to G Programming, contains the following chapters.

• Chapter 2, Creating VIs, explains how to create a VI including the
front panel, which is the user interface, and the block diagram, which
is the source code. Once you create a VI, you can use it in other VIs.

• Chapter 3, Loops and Charts, shows you how to rep eat portio ns of the
block diagram using a While Loop and a For Loop. This chapter also
explains how to display graphically multiple points, one at a time, on
a chart.

• Chapter 4, Case and Sequence Structures and the Formula Node,
explains how to use the Case structure, which is a conditional structure,
the Sequence structure, which aids in establishing ex ecution order , and
the Formula Node, which aids in executing mathematical formulas.

• Chapter 5, Arrays, Cl usters, and Gr aphs, shows how to display a
group or array of data points on a graph. You can pass scale parameters
as well as an array of data points to a graph by creating a cluster, which
is a group of data different data types.

• Chapter 6, Strings and File I/O, introduces string controls and
indicators and file i npu t and out pu t operat io ns .

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National Instruments Corporation xxiii LabVIEW User Manual

About This Manual

Part II, I/O Interfaces

This section contains basic information on the interfaces to which you can
input and output data, which are data acquisition, GPIB, serial, and VXI.
Refer to the Data Acquisition Basics Manual for basic information on
real-time data acquisition. VISA (Virtual Instrument Software
Architecture) is a single software library that interfaces with GPIB, serial,
and VXI instruments. LabVIEW applications developed especially for a
specific instrument are called instrument drivers. National Instruments
provides several instrument drivers using the VISA library , but you can also
build your own instrument drivers.

Part II, I/O Interfaces, contains the following chapters.

• Chapter 7, Getting Started with a LabVIEW Instrument Driver,

• Chapter 8, LabVIEW VISA Tutorial, shows you how to implement

• Chapter 9, Introduction to LabVIEW GPIB Functions, explains how

• Chapter10, Serial Port VIs, explains the important factors that affect

explains how to create and use National Instruments instrument
drivers.

common VISA applications using message-based and register-based
communication as well as events and locking.

the GPIB operates and the difference between the IEEE 488 and
IEEE 488.2 interface.

serial communication.

Part III, Analysis

This section contains basic information on analysis of data, signal
processing, signal generation, linear algebra, curve fitting, probability, and
statistics.

Part III, Analysis, contains the following chapters.

• Chapter11, Introduction to Analysis in LabVIEW, introduces concepts
that apply to all analysis applications, including supported
functionality, notation and naming conventions, and sampling signal
methods.

• Chapter12, Signal Generation, explains how to produce signals using
the normalized frequency and how to build a simulated function
generator.

• Chapter13, Digital Signal Processing, shows the difference
between the Fast Fourier Transform (FFT) and the Discrete Fourier
Transform (DFT).

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• Chapter14, Smoothing Wind ow s, explains how using windows
prevents spectral leakage and improves the analysis of acquired
signals.

• Chapter15, Spectrum Analysis and Measurement, shows how to
determine the amplitude and phase sp ectrum, develop a spectrum
analyzer, and determine the total harmonic distortion (THD).

• Chapter16, Filtering, explains how to filter unnecessary frequencies
from signals using infinite impulse response filters (IIR), finite
impulse response filters (FIR), and nonlinear filters.

• Chapter17, Curve Fitting, shows how to extract information from a
data set to create a data trend description.

• Chapter18, Linear Algebra, explains how to perform matrix
computation and analysis.

• Chapter19, Probability and Statistics, explains some fundamental
concepts of probability and statistics, and shows how to use these
concepts in solving real-world problems.

Part IV, Network and Interapplication Communication

This section contai ns basic inform ation abou t network an d interapp lication
communication.

About This Manual

Part IV, Network and Interapplication Communication, contains the
following chapters.

• Chapter20, Introduction to Communication, introduces the way
LabVIEW handles networking and interapplication communication.

• Chapter21, TCP and UDP, explains basic concepts of Transmission
Control Protocol (TCP), Internet Protocol (IP ), and internet addres ses.

• Chapter22, Acti veX Support, shows how LabVIEW can be an ActiveX
server and client. ActiveX is the same as OLE Automation
communication.

• Chapter23, Using DDE, explains ho w to use Dynamic Data Exchange
(DDE) to communicate between Windows applications. DDE can be
used in a client, a server, and across a network.

• Chapter24, AppleEvents, shows how AppleEvents are used to
communicate between LabVIEW and other Macintosh applications.
LabVIEW can be an AppleEvents server and client.

• Chapter25, Program-to-Program Communication, explains how
LabVIEW can communicate to other Macintosh applications using
Program-to-Program Communication (PPC).

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About This Manual

Part V, Advanced G Programming

This section contains information on VI customization; programmatic
control of front panel objects, VIs, and LabVIEW; and tips on how to
design complex applications.

Part V, Advanced G Programming, contains the following chapters.

• Chapter26, Customizing VIs, shows how to use VI Setup… and
VI Node Setup… to customize the appearance and execution behavior
of a VI when it is running.

• Chapter27, Front Panel Object Attributes, describes objects called
attribute nodes, which are special block diagram nodes that control the
appearance and functional characteristics of controls and indicators.

• Chapter28, Program Design, explains techniques to use when
creating programs and offers programming-style guidelines.

• Chapter29, Where to Go from Here, provides information about
resources you can use to create your applications successfully.

Appendices, Glossary, and Index

•AppendixA, Analysis References, lists the reference material used to
produce the Analysis VIs in LabVIEW . These references contain more
information on the theories and algorithms implemented in the
analysis library.

•AppendixB, Common Questions, answers common questions about
LabVIEW networking communications and Instrument I/O ,
specifically GPIB and serial I/O.

•AppendixC, Customer Communication, contains forms to help you
gather the information necessary to help us solve your technical
problems and a form you can use to comment on the product
documentation.

•The Glossary contains an alphabetical list of terms used in this manual,
including abbreviations, acronyms, metric prefixes, mnemonics, and
symbols.

•The Index contains an alphabetical list of key terms and topics in this
manual, including the page where you can find each one.

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About This Manual

Conventions Used in This Manual

The following conventions are used in this manual:

< > Angle brackets enclose the name of a key on the keyboard—for example,

<shift>. Angle brackets containing numbers separated by an ellipsis
represent a range of values associated with a bit or signal name—
for example, DBIO<3..0>.

- A hyphen between two or more key names enclosed in angle brackets
denotes that you should simultaneously press the named keys—
for example, <Control-Alt-Delete>.

» The » symb ol leads you throu gh nested menu ite ms and dialog box op tions

to a final action. The sequence File»Page Setup»Options» Substitute
Fonts directs you to pull down the File menu, select the Page Setup item,
select Options, and finally select the Substitute Fonts options from the
last dialog box.

This icon to the left of bold te xt denotes the be ginning of an acti vity, which
contains step-by-step instructions you can follow to learn more about
LabVIEW.

This icon to the left of bold text denotes the end of an activity, which
contains step-by-step instructions you can follow to learn more about
LabVIEW.

This icon to the left of bold italicized text denotes a note, which alerts you
to important information.

!

bold Bold text denotes the names of menus, menu items, parameters, dialo g

bold italic Bold italic text denotes an activity objective, note, caution, or warning.

bold monospace Bold monospace text denotes messages and responses that the computer

italic Italic text denotes variables, emphasis, a cross reference, or an introduction

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National Instruments Corporation xxvii LabVIEW User Manual

This icon to the left of bold italicized text denotes a caution, which advises
you of precautions to take to avoid injury, data loss, or a system crash.

boxes, dialog box buttons or options, icons, windows, Windows 95 tabs,
or LEDs.

automatically prints to the screen.

to a key concept. This font also denotes text from which you supply the
appropriate word or value, as in Windows 3.x.

About This Manual

monospace Text in this font denotes text or characters that you should literally enter

from the keyboard, sections of code, programming examples, and syntax
examples. This font is also used for the proper n ames of disk d ri ves, p aths,
directories, progr ams, su bprog rams, s ubrouti nes, d e vice n ames, functio ns,
operations, variables, filenames and extensions, and for statements and
comments taken from programs.

paths Paths in this manual are denoted using backslashes (\) to separate drive

names, director i es, fol ders, and files.

Platform Text in this font denotes information related to a specific platform.

Related Documentation

• G Programming Reference Manual

• LabVIEW Data Acquisition Basics Manual

• LabVIEW Function and VI Reference Manual

• LabVIEW QuickStart Guide

• LabVIEW Online Reference, available by selecting

Help»Online Reference

• LabVIEW Online Tutorial
LabVIEW dialog box

• G Programming Quick Reference Card

• LabVIEW Getting Starte d Card

• LabVIEW Release Notes

• LabVIEW Upgrade Notes

(Windows only), which you launch f rom t he

Customer Communication

National Instruments wants to receive your comments on our products
and manuals. We are interested in the applications you develop with our
products, and we want to help if you have problems with them. To make it
easy for you to contact us, this manual contains comment and configuration
forms for you to complete. These forms are in Appendix C, Customer

Communication, at the end of this manual.

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Introduction

This chapter introduces the unique LabVIEW approach to programming.
It also explains how to start using LabVIEW to develop programs. The
chapter refers you to other chapters or manuals for more information.

What Is LabVIEW?

LabVIEW is a program development enviro nment, much like modern C
or BASIC development environments, and National Instr uments
LabWindows/CVI. However, LabVIEW is different from those
applications in one important respect. Other programming systems use

text-based languages to create lines of code, while LabVIEW uses a
graphical programming language, G, to create programs in block diagram

form.
LabVIEW, like C or BASIC, is a general-purpose programming system

with extensive libraries of functions for any programming task. LabVIEW
includes libraries for data acquisition, GPIB and serial instrument control,
data analysis, data presentation, and data storage. LabVIEW also includes
conventional program development tools, so you can set breakpoints,
animate the execution to see how data passes through the program, and
single-step through the program to make debugging and program
development easier.

1

How Does LabVIEW Work?

LabVIEW is a general-purpose programming system, but it also includes
libraries of functions and devel opment tool s designed specifically fo r data
acquisition and instrument control. LabVIEW programs are called virtual
instruments (VIs) because their appearance and operation can imitate actual
instruments. However, VIs are similar to the functions of conventional
language programs.

A VI consists of an interactive user interface, a dataflow diagram that
serves as the source code, and icon connections that allow the VI to be

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National Instruments Corporation 1-1 LabVIEW User Manual

Chapter 1 Introduction

called from higher level VIs. More specifically, VIs are structured as
follows:

• The interactive user interface of a VI is called the front panel,
because it simulates the pane l o f a physica l instru ment. T he fr ont
panel can contain knobs, push buttons, graphs, and othe r controls
and indicators. Yo u ente r data using a m ouse and k eyboa rd , and
then view th e re su lt s o n t h e co mpu ter sc re en .

• The VI receives instructions from a block diagram, which you
construct in G. The block diagram is a pictorial solution to a
programming problem. The block diagram is also the sourc e code
for the VI.

• VIs are hierarchical and modular. You can use them as top-level
programs, or as sub pro gram s within o the r p rogra ms. A VI w ithin
another VI is called a su bVI. The icon and connector of a VI work
like a graphical parameter list so that other VIs can pass data to a
subVI.

With these features, LabVIEW promotes and adheres to the concept of
modular programming. You divide an application into a series of tasks,
which you can divide again until a complicated application becomes a
series of simple subtasks. You build a VI to accomplish each subtask and
then combine those VIs on another block diagram to accomplish the larger
task. Finally, your top-level VI contains a collection of subVIs that
represent application functions.

Because you can execute each subVI by itself, apart from the rest of the
application, debugging is much easier. Furthermore, many low-level
subVIs often perform tas ks common to sev eral applications, s o that you can
develop a specialized set of subVIs well-suited to applications you are
likely to construct.

G Programming

G is the easy to use graphical data flow programming language on which
LabVIEW is based. G simplifies scientific computation , process
monitoring and control, and test and measurement applications, and you
also can use it for a wide variety of other applications.

Part I, Introduction to G Programming, covers the functionality of G that

you need to get started with most LabVIEW applications . For a more
extensive explanation of LabVIEW functionality, see the G Programming
Reference Manual.

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Chapter 1 Introduction

The basic concepts of G that are covered in this manual are described in the
following list.

• VIs—Virtual instruments (VIs) have three main parts: the front panel,
the block diagram, and the icon/connector. The front panel specifies
the user interface of the VI. The block diagram consists of the
executable code that you create using nodes, terminals, and wires.
With the icon/connector, you can use a VI as a subVI in the block
diagram of another VI. For more information about VIs, refer to
Chapter 2, Creating VIs and Chapter 26, Customizing VIs.

• Loops and Charts—G has two structures to repeat execution of a
sub-diagram—the While Loop and the For Loop. Both structures are
resizable boxes. You place the subdiagram to be repeated inside the
border of the loop structure. The While Loop executes as long as the
value at the conditional terminal is TRUE. The For Loop executes a set
number of times. Charts are used to d isplay real-time trend information
to the operator. For more information about loops and charts, refer to
Chapter 3, Loops and Charts.

• Case and Sequence Structures—The Case structure is a co nditional
branching control structure, which executes a subdiagram based on
certain input. A Sequence structure is a program control structure that
executes its subdiagrams in numeric order. For more information about
Case or Sequence structures, refer to Chapter 4, Case and Sequence

Structures and the Formula Node.

• Attribute Nodes—Attribute nodes are special block diagra m nodes
that you can use to control the appearance and functional
characteristics of controls and indicators. For mor e info rmation abo ut
attribute nodes, refer to Chapter 27, Front Panel Object Attributes.

• Arrays, Clusters and Graphs—An array is a resizable collection of
data elements of the same type. A cluster is a statically sized collection
of data elements of the same or different types. Graphs commo nly are
used to display data. For more informa tion about arrays, clusters, and
graphs, refer to Chapter 5, Arrays, Clusters, and Graphs.

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National Instruments Corporation 1-3 LabVIEW User Manual

Chapter 1 Introduction

Organization of the LabVIEW System (Windows)

After you have completed the installation, as described in th e LabVIEW
Release Notes that come with your software, your LabVIEW directory

should contain the following files.

•

LABVIEW.EXE—This is the LabVI EW program. Launch this progr am

to start LabVIEW .

•

vi.lib directory—Contains libraries of VIs that are included with

LabVIEW , including GPIB, analysis, and data acquisition (DAQ) VIs.
Most of these are available from the Functions palette.

•

examples directory—Contains numerous subdirectories of e xamples.

This directory also contains a VI called
guide to the examples.

•

serpdrv and daqdrv—These files serve as part of LabVIEW’s

interface to the serial port, and DAQ communication, respectively.
These files must be in the same directory as

•

resource directory

–

labview.rsc, lvstring.rsc, and lvicon.rsc—Data files

used by the LabVIEW application

–

(Windows 3.1)

lvdevice.dll—This file provides timing services
to LabVIEW and must be in the same directory as
LabVIEW to run.

–

(Windows 3.1)

lvimage.dll

images created using a variety of graphics programs.

–

labview50

.tlb

—This file is a type library to enable LabVIEW

to act as an ActiveX server.

–

ole_container.dll—This file enables LabVIEW to display

and update ActiveX containers.

–

lvwutil32.dll—This file is used by the Solution Wizard,

which builds DAQ and Instrument I/O examples based on your
criteria.

–

lvjpeg.dll and lvpng.dll—These files provide support to

display JPEG and PNG graphics in HTML files when you print VI
documentation to an HTML file.

•

Cintools directory—Contains files necessary to build Code Inter face

Nodes (CINs), which are a means to link C code to LabVIEW VIs.

•

visarc file—Serves as part of LabVIEW’s interface to VISA (V irtual

Instrument Software Architecture). VISA provides a single interface
library for controlling VXI, GPIB, and Serial instruments.

readme.vi that serves as a

vi.lib.

—This file allows LabVIEW to load

vi.lib for

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