Virtual Instrumentation With LabVIEW

Course Goals
Understand the components of a Virtual Instrument Introduce LabVIEW and common LabVIEW functions Build a simple data acquisition application Create a subroutine in LabVIEW Work with Arrays, Clusters, and Structures Learn About Printing & Documentation Features Develop in Basic Programming Architectures Publish VIs on the Web

Section I
LabVIEW terms Components of a LabVIEW application LabVIEW programming tools Creating an application in LabVIEW

LabVIEW Programs Are Called Virtual Instruments (VIs)

Front Panel
Controls = Inputs Indicators = Outputs

Block Diagram
Accompanying program for front panel Components wired together

VI Front Panel
Front Panel Toolbar Boolean Control Icon

Graph Legend

Waveform Graph Plot Legend Scale Legend

VI Block Diagram
Block Diagram Toolbar Divide Function

SubVI Graph Terminal Wire Data

While Loop Structure

Numeric Constant

Timing Function

Boolean Control Terminal

Express VIs, VIs and Functions

Express VIs: interactive VIs with configurable dialog page Standard VIs: modularized VIs customized by wiring Functions: fundamental operating elements of LabVIEW; no front panel or block diagram

Function

Express VI

Standard VI

Controls and Functions Palettes

Controls Palette
(Front Panel Window)

Functions Palette
(Block Diagram Window)

Tools Palette
Floating Palette Used to operate and modify front panel and block diagram objects.
Automatic Selection Tool Operating Tool Positioning/Resizing Tool Labeling Tool Wiring Tool Shortcut Menu Tool Scrolling Tool Breakpoint Tool Probe Tool Color Copy Tool Coloring Tool

Status Toolbar
Run Button Continuous Run Button Abort Execution Pause/Continue Button Text Settings Align Objects Distribute Objects Reorder Resize front panel objects Execution Highlighting Button Step Into Button Step Over Button Step Out Button

Additional Buttons on the Diagram Toolbar

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Open and Run a Virtual Instrument

Example finder

Creating a VI
Front Panel Window

Block Diagram Window

Control Terminals

Indicator Terminals

Creating a VI Block Diagram

Wiring Tips Block Diagram

Wiring Hot Spot Click To Select Wires

Use Automatic Wire Routing

Clean Up Wiring

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Dataflow Programming
Block diagram executes dependent on the flow of data; 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

Help Options
Context Help
Online help Lock help Simple/Complex Diagram help Ctrl + H

Online reference
All menus online Pop up on functions in diagram to access online info directly

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Exercise 1 - Convert C to F

Debugging Techniques
Finding Errors
Click on broken Run button Window showing error appears

Execution Highlighting
Click on Execution Highlighting button; data flow is animated using bubbles. Values are displayed on wires.

Probe
Right-click on wire to display probe and it shows data as it flows through wire segment You can also select Probe tool from Tools palette and click on wire

Section II SubVIs

What is a subVI? Making an icon and connector for a subVI Using a VI as a subVI

Block Diagram Nodes

Icon Expandable Node Expanded Node

Function Generator VI Same VI, viewed three different ways Yellow field designates a standard VI Blue field designates an Express VI

SubVIs
A SubVI is a VI that can be used within another VI Similar to a subroutine Advantages
Modular Easier to debug Dont have to recreate code Require less memory

Icon and Connector

Icon Terminals

An icon represents a VI in other block diagrams A connector shows available terminals for data transfer

Connector

SubVIs

Sub VIs

Steps to Create a SubVI

Create the Icon Create the Connector Assign Terminals Save the VI Insert the VI into a Top Level VI

Create the Icon

Right-click on the icon in the block diagram or front panel

Create the Connector

Right click on the icon pane (front panel only)

Assign Terminals

Save 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 VIs into a single file, ideal for transferring entire applications across computers

Insert the SubVI into a Top Level VI

Accessing user-made subVIs
Functions >>All Functions >> Select a VI Or Drag icon onto target diagram

Tips for Working in LabVIEW

Keystroke Shortcuts
<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)

Tools Options Set Preferences in LabVIEW VI Properties Configure VI Appearance, Documentation, etc.

Section III Data Acquisition

Data acquisition (DAQ) basics Connecting Signals Simple DAQ application
Sensors
Cable Terminal Block DAQ Device

Computer

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

DAQ Data Acquisition

Temperature Acquisition using the DAQ Assistant

Data Acquisition Terminology

Resolution - Determines How Many Different Voltage Changes Can Be Measured
Larger Resolution Smaller range More Precise Representation of Signal More Precise Representation of Signal

Range - Minimum and Maximum Voltages Gain - Amplifies or Attenuates Signal for Best Fit in Range

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Hardware Connections
BNC-2120 SC-2075 NI-ELVIS SCB-68

Exercise 2 Simple Data Acquisition

Complete Convert C to F.vi, then create Thermometer.vi.

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Section IV Loops and Charts

For Loop While Loop Charts Multiplots

Loops
While Loops
Have Iteration Terminal Always Run at least Once Run According to Conditional Terminal

For Loops
Have Iteration Terminal Run According to input N of Count Terminal

Loops (cont.)
1. Select the loop 2. Enclose code to be repeated

3. Drop or drag additional nodes and then wire

Charts

Waveform chart special numeric indicator that can display a history of values Controls >> Graph Indicators >> Waveform Chart

Wiring Data into Charts

Single Plot Charts Multiplot Charts

Exercise 3 Using loops

Students build Use a loop.vi.

Section V Arrays & File I/O

Build arrays manually Have LabVIEW build arrays automatically Write to a spreadsheet file Read from a spreadsheet file

Adding an Array to the Front Panel

From the Controls >> All Controls >> Array and Cluster subpalette, select the Array Shell

Drop it on the screen.

Adding an Array (cont.)

Place data object into shell (i.e. Numeric Control)

Creating an Array with a Loop

Loops accumulate arrays at their boundaries

Creating 2D Arrays

File I/O
File I/O passing data to and from files - Files can be binary, text, or spreadsheet - Write/Read LabVIEW Measurements file (*.lvm) Writing to LVM file Reading from LVM file

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

Exercise 4 Analyzing and Logging Data

Students build Temperature Logger.vi

Section VI Array Functions & Graphs

Basic Array Functions Use graphs Create multiplots with graphs

Array Functions Basics

Functions >> All functions>> Array

Array Functions Build Array

Graphs
Selected from the Graph palette of Controls menu
Controls>>All Controls>>Graphs Waveform Graph Plot an array of numbers against their indices Express XY Graph Plot one array against another Digital Waveform Graph Plot bits from binary data

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Graphs

Right-Click on the Graph and choose Properties to Interactively Customize

Exercise 5 Using Waveform Graphs

Section VII Strings, Clusters, & Error Handling

Strings Creating Clusters Cluster Functions Error I/O

Strings
A string is a sequence of displayable or nondisplayable characters (ASCII) Many uses displaying messages, instrument control, file I/O String control/indicator is in the Controls Text Control or Text Indicator

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

Creating a Cluster
1. Select a Cluster shell 2. Place objects inside the shell Controls >> All Controls >> Array & Cluster

Cluster Functions
In the Cluster subpalette of the Functions>>All functions palette Can also be accessed by right-clicking on the cluster terminal

(Terminal labels reflect data type) Bundle

Bundle By Name

Cluster Functions
Unbundle

Unbundle By Name
Unbundled cluster in the diagram

Error Clusters
Error cluster contains the following information: Boolean to report whether error occurred Integer to report a specific error code String to give information about the error

Error Handling Techniques

Error information is passed from one subVI to the next If an error occurs in one subVI, all subsequent subVIs are not executed in the usual manner Error Clusters contain all error conditions Automatic Error Handling

error clusters

Section VIII - Case & Sequence Structures, Formula Nodes

Case Structures
In the Structures subpalette of Functions palette Enclose nodes or drag them inside the structure Stacked like a deck of cards, only one case visible Functions >> Execution control

Exercise 6 Error Clusters & Handling

Sequence Structures
In the Execution Control subpalette of Functions palette Executes diagrams sequentially Right-click to add new frame

Formula Nodes
In the Structures subpalette 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
Note semicolon

Section IX Printing & Documentation

Print From File Menu to Printer, HTML, Rich Text File Programmatically Print Graphs or Front Panel Images Document VIs in VI Properties Documentation Dialog Add Comments Using Free Labels on Front Panel & Block Diagram

Printing
File Print Gives Many Printing Options
Choose to Print Icon, Front Panel, Block Diagram, VI Hierarchy, Included SubVIs, VI History

Print Panel.vi (Programmatically Prints a Front Panel)

Functions All Functions Application Control

Generate & Print Reports (Functions Output Report)

Documenting VIs
VI Properties Documentation
Provide a Description and Help Information for a VI

VI Properties Revision History

Track Changes Between Versions of a VI

Individual Controls Description and Tip

Right Click to Provide Description and Tip Strip

Use Labeling Tool to Document Front Panels & Block Diagrams

Section X Basic Programming Architecture

Simple VI Architecture General VI Architecture State Machine Architecture

Simple VI Architecture
Functional VI that produces results when run No start or stop options Suitable for lab tests, calculations Example: Convert C to F.vi

General VI Architecture
Three Main Steps
Startup Main Application Shutdown

State Machine Architecture

Advantages
Can go from any state from any other Easy to modify and debug

Disadvantages
Can lose events if two occur at the same time
States: 0: Startup 1: Idle 2: Event 1 3: Event 2 4: Shutdown

Exercise 7 Simple State Machine

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Section XI Remote Front Panels

View & Control LabVIEW Front Panels from a Web Browser Requires no programming Remote clients see live front panel updates Multiple clients can view the same panel simultaneously Only one client can control the front panel at a time

Remote Panel Web Publishing Tool

Tools Web Publishing Tool Click Save to Disk and VI is embedded into an HTML file After file is saved, it can be reopened and customized in any HTML editor

Remote Front Panels - Resources

NI Developer Zone (zone.ni.com)
Search for Remote Front Panel Tutorials & Instructions Are Available for Download Information on Incorporating Web Cameras into Remote Panel Applications

Section XII Additional Topics

Property Nodes Local Variables Global Variables DataSocket Binary File I/O

Where Do I Go From Here?

Example programs (Help Find Examples) LabVIEW Student Edition (www.ni.com/labviewse) Web resources (ni.com)
NI Developer Zone (zone.ni.com) Application Notes Info-labview newsgroup (www.info-labview.org/) Instrument Driver Library (www.ni.com/idnet)