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LabVIEW

TM

Getting Started with LabVIEW

Getting Started with LabVIEW

August 2006 323427C-

Support

Worldwide Technical Support and Product Information

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For further support information, refer to the Technical Support and Professional Services appendix. To comment on National Instruments documentation, refer to the National Instruments Web site at ni.com/info and enter the info code feedback.

© 2003–2006 National Instruments Corporation. All rights reserved.

DAMAGE, INJURY, OR DEATH, THE USER OR APPLICATION DESIGNER MUST TAKE REASONABLY PRUDENT STEPS TO PROTECT AGAINST SYSTEM FAILURES, INCLUDING BUT NOT LIMITED TO BACK-UP OR SHUT DOWN MECHANISMS. BECAUSE EACH END-USER SYSTEM IS CUSTOMIZED AND DIFFERS FROM NATIONAL INSTRUMENTS' TESTING PLATFORMS AND BECAUSE A USER OR APPLICATION DESIGNER MAY USE NATIONAL INSTRUMENTS PRODUCTS IN COMBINATION WITH OTHER PRODUCTS IN A MANNER NOT EVALUATED OR CONTEMPLATED BY NATIONAL INSTRUMENTS, THE USER OR APPLICATION DESIGNER IS ULTIMATELY RESPONSIBLE FOR VERIFYING AND VALIDATING THE SUITABILITY OF NATIONAL INSTRUMENTS PRODUCTS WHENEVER NATIONAL INSTRUMENTS PRODUCTS ARE INCORPORATED IN A SYSTEM OR APPLICATION, INCLUDING, WITHOUT LIMITATION, THE APPROPRIATE DESIGN, PROCESS AND SAFETY LEVEL OF SUCH SYSTEM OR APPLICATION.

© National Instruments Corporation v Getting Started with LabVIEW

Contents

About This Manual

Conventions ...................................................................................................................ix

Contents

© National Instruments Corporation vii Getting Started with LabVIEW

Visually Comparing Two Voltage Readings...................................................4- Communicating with an Instrument ..............................................................................4- Finding and Installing Instrument Drivers (Windows and Linux) ..................4- Selecting an Instrument Using the Instrument I/O Assistant ..........................4- Acquiring and Parsing Information for an Instrument ....................................4- Wiring a Command to an Instrument ..............................................................4- Summary ........................................................................................................................4- DAQ Assistant Express VI..............................................................................4- Tasks................................................................................................................4- Instrument Drivers...........................................................................................4- Instrument I/O Assistant Express VI...............................................................4-

Chapter 5

Using Other LabVIEW Features

All Controls and Indicators............................................................................................5- All VIs and Functions ....................................................................................................5- VIs ...................................................................................................................5- Functions .........................................................................................................5- Data Types .....................................................................................................................5- Dynamic Data Type.........................................................................................5- When to Use Other LabVIEW Features ........................................................................5-

Appendix A

Technical Support and Professional Services

Glossary

Index

About This Manual

Getting Started with LabVIEW x ni.com

monospace bold Bold text in this font denotes the messages and responses that the computer automatically prints to the screen. This font also emphasizes lines of code that are different from the other examples.

Platform Text in this font denotes a specific platform and indicates that the text following it applies only to that platform.

right-click (Mac OS) Press -click to perform the same action as a right-click.

Related Documentation

The following documents contain information that you may find helpful as you read this manual:

• LabVIEW Release Notes —Use these release notes to install and uninstall LabVIEW. The release notes also describe the system requirements for the LabVIEW software, including the LabVIEW Application Builder.
• LabVIEW Help —Use the LabVIEW Help to access information about LabVIEW programming concepts, step-by-step instructions for using LabVIEW, and reference information about LabVIEW VIs, functions, palettes, menus, tools, properties, methods, events, dialog boxes, and so on. The LabVIEW Help also lists the LabVIEW documentation resources available from National Instruments. Access the LabVIEW Help by selecting Help»Search the LabVIEW Help.
• LabVIEW Quick Reference Card —Use this card as a reference for information about help resources, keyboard shortcuts, data type terminals, and tools for editing, execution, and debugging.

© National Instruments Corporation 1-1 Getting Started with LabVIEW

Getting Started with LabVIEW

Virtual Instruments

LabVIEW programs are called virtual instruments, or VIs, because their appearance and operation imitate physical instruments, such as oscilloscopes and multimeters. LabVIEW contains a comprehensive set of tools for acquiring, analyzing, displaying, and storing data, as well as tools to help you troubleshoot code you write.

In LabVIEW, you build a user interface, or front panel, with controls and indicators. Controls are knobs, push buttons, dials, and other input mechanisms. Indicators are graphs, LEDs, and other output displays. After you build the user interface, you add code using VIs and structures to control the front panel objects. The block diagram contains this code.

You can use LabVIEW to communicate with hardware such as data acquisition, vision, and motion control devices, as well as GPIB, PXI, VXI, RS232, and RS485 instruments.

Building a Virtual Instrument

In the following exercises, you will build a VI that generates a signal and displays that signal in a graph. After you complete the exercises, the front panel of the VI will look similar to the front panel in Figure 1-1.

You can complete the exercises in this chapter in approximately 40 minutes.

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Figure 1-2. Getting Started Window

The Getting Started window disappears when you open an existing file or create a new file. The Getting Started window reappears when you close all open front panels and block diagrams. You also can display the window from the front panel or block diagram by selecting View»Getting Started Window.

Opening a New VI from a Template

LabVIEW provides built-in template VIs that include the subVIs, functions, structures, and front panel objects you need to get started building common measurement applications.

Complete the following steps to create a VI that generates a signal and displays it on the front panel.

1. Launch LabVIEW.

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2. In the Getting Started window, click the New or VI from Template link to display the New dialog box.
3. From the Create New list, select VI»From Template»Tutorial (Getting Started)»Generate and Display. This template VI generates and displays a signal. A preview and a brief description of the template VI appear in the Description section. Figure 1-3 shows the New dialog box and the preview of the Generate and Display template VI.

Figure 1-3. New Dialog Box

4. Click the OK button to create a VI from the template. You also can double-click the name of the template VI in the Create New list to create a VI from a template.

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2. If you are a new LabVIEW user, the Controls palette opens with the Express subpalette visible by default. If you do not see the Express subpalette, click Express on the Controls palette to display the Express subpalette.

Figure 1-4. Controls Palette

3. Move the cursor over the icons on the Express subpalette to locate the Numeric Controls palette. When you move the cursor over icons on the Controls palette, the name of the subpalette, control, or indicator appears in a tip strip below the icon.
4. Click the Numeric Controls icon to display the Numeric Controls palette.
5. Click the knob control on the Numeric Controls palette to attach the control to the cursor, then place the knob on the front panel to the left of the waveform graph. You will use this knob in a later exercise to control the amplitude of a signal.
6. Select File»Save As and save the VI as Acquiring a Signal.vi in an easily accessible location.

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Changing a Signal Type

The block diagram has a blue icon labeled Simulate Signal. This icon represents the Simulate Signal Express VI. The Simulate Signal Express VI simulates a sine wave by default.

Complete the following steps to change this signal to a sawtooth wave.

1. Display the block diagram by pressing the <Ctrl-E> keys or by clicking the block diagram. Locate the Simulate Signal Express VI, shown at left. An Express VI is a component of the block diagram that you can configure to perform common measurement tasks. The Simulate Signal Express VI simulates a signal based on the configuration that you specify.
2. Right-click the Simulate Signal Express VI and select Properties from the shortcut menu to display the Configure Simulate Signal dialog box. (Mac OS) Press -click to perform the same action as right-click. You also can double-click the Express VI to display the Configure Simulate Signal dialog box. If you wire data to an Express VI and run it, the Express VI displays real data in the configuration dialog box. If you close and reopen the Express VI, the VI displays sample data in the configuration dialog box until you run the VI again.
3. Select Sawtooth from the Signal type pull-down menu. The waveform on the graph in the Result Preview section changes to a sawtooth wave. The Configure Simulate Signal dialog box should appear similar to Figure 1-5.

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Wiring Objects on the Block Diagram

To use the knob to change the amplitude of the signal, you must connect two objects on the block diagram.

Complete the following steps to wire the knob to the Amplitude input of the Simulate Signal Express VI.

1. On the block diagram, move the cursor over the Knob terminal, shown at left. The cursor becomes an arrow, or the Positioning tool, shown at left. Use the Positioning tool to select, position, and resize objects.
2. Use the Positioning tool to select the Knob terminal and make sure it is to the left of the Simulate Signal Express VI and inside the gray loop, shown at left. The terminals inside the loop are representations of front panel controls and indicators. Terminals are entry and exit ports that exchange information between the front panel and block diagram.
3. Deselect the Knob terminal by clicking a blank space on the block diagram. If you want to use a different tool with an object, you must deselect the object to switch the tool.
4. Move the cursor over the arrow on the Knob terminal, shown at left. The cursor becomes a wire spool, or the Wiring tool, shown at left. Use the Wiring tool to wire objects together on the block diagram.
5. When the Wiring tool appears, click the arrow on the Knob terminal and then click the arrow on the Amplitude input of the Simulate Signal Express VI, shown at left, to wire the two objects together. A wire appears and connects the two objects. Data flows along this wire from the Knob terminal to the Express VI.
6. Select File»Save to save the VI.

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Running a VI

Running a VI executes the solution.

Complete the following steps to run the Acquiring a Signal VI.

1. Display the front panel by pressing the <Ctrl-E> keys or by clicking the front panel.
2. Click the Run button or press the <Ctrl-R> keys to run the VI.
3. Move the cursor over the knob. The cursor becomes a hand, or the Operating tool, shown at left. Use the Operating tool to change the value of a control.
4. Using the Operating tool, turn the knob to adjust the amplitude of the sawtooth wave. The amplitude of the sawtooth wave changes as you turn the knob. As you change the amplitude, the Operating tool displays a tip strip that indicates the numeric value of the knob. The y-axis on the graph scales automatically to account for the change in amplitude. To indicate that the VI is running, the Run button changes to a darkened arrow, shown at left. You can change the value of most controls while a VI runs, but you cannot edit the VI in other ways while the VI runs.
5. Click the STOP button, shown at left, to stop the VI. The STOP button stops the VI after the VI completes the current iteration. The Abort Execution button, shown at left, stops the VI immediately, before the VI finishes the current iteration. Aborting a VI that uses external resources, such as external hardware, might leave the resources in an unknown state by not resetting or releasing them properly. Design the VIs you create with a stop button to avoid this problem.