Getting Started with LabVIEW

LabVIEW
TM
Getting Started with LabVIEW
Getting Started with LabVIEW
August 2005
373427A-01
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Contents
About This Manual
Conventions ...................................................................................................................ix
Related Documentation..................................................................................................x
Chapter 1
Getting Started with LabVIEW Virtual Instruments
Building a Virtual Instrument ........................................................................................1-1
Launching LabVIEW ......................................................................................1-2
Opening a New VI from a Template ...............................................................1-3
Adding a Control to the Front Panel................................................................1-5
Changing a Signal Type ..................................................................................1-6
Wiring Objects on the Block Diagram ............................................................1-8
Running a VI ...................................................................................................1-9
Modifying a Signal ..........................................................................................1-10
Displaying Two Signals on a Graph................................................................1-12
Customizing a Knob Control...........................................................................1-13
Customizing a Waveform Graph.....................................................................1-15
Summary ........................................................................................................................1-16
New Dialog Box and Template VIs ................................................................1-16
Front Panel.......................................................................................................1-16
Property Dialog Boxes ....................................................................................1-17
Block Diagram.................................................................................................1-17
Express VIs......................................................................................................1-17
Chapter 2
Analyzing and Saving a Signal
Building a VI from a Template......................................................................................2-1
Opening a New VI from a Template ...............................................................2-1
Modifying the Block Diagram.........................................................................2-3
Modifying the Front Panel...............................................................................2-4
Analyzing the Amplitude of a Signal ..............................................................2-5
Adding a Warning Light..................................................................................2-6
Setting a Warning Level Limit ........................................................................2-7
Warning the User.............................................................................................2-8
Configuring a VI to Save Data to a File ..........................................................2-9
Saving Data to a File .......................................................................................2-10
Adding a Button That Stores Data When Pressed...........................................2-10
© National Instruments Corporation
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Saving Data When Prompted by a User.......................................................... 2-11
Viewing Saved Data........................................................................................ 2-12
Summary........................................................................................................................ 2-13
LabVIEW Documentation Resources ............................................................. 2-13
Controls and Indicators ................................................................................... 2-13
Saving Data ..................................................................................................... 2-13
Errors and Broken Wires................................................................................. 2-14
Chapter 3
Customizing a VI
Building a VI from a Blank VI...................................................................................... 3-1
Opening a Blank VI ........................................................................................ 3-1
Adding an Express VI That Simulates a Signal.............................................. 3-2
Searching the Help and Modifying a Signal ................................................... 3-3
Customizing a User Interface from the Block Diagram ................................. 3-4
Configuring a VI to Run Continuously until the User Stops It....................... 3-5
Searching for Examples .................................................................................. 3-6
Controlling the Speed of Execution ................................................................ 3-7
Using a Table to Display Data ........................................................................ 3-8
Summary........................................................................................................................ 3-9
Using the LabVIEW Help Resources ............................................................. 3-9
Customizing the Block Diagram Code ........................................................... 3-10
Creating Controls and Indicators ...................................................... 3-10
Controlling When a VI Stops Running............................................. 3-11
Displaying Data in a Table ............................................................... 3-11
Chapter 4
Optional: Acquiring Data and Communicating with Instruments
Acquiring a Signal......................................................................................................... 4-1
Creating an NI-DAQmx Task ......................................................................... 4-2
Testing the Task .............................................................................................. 4-4
Graphing Data from a DAQ Device ............................................................... 4-4
Editing an NI-DAQmx Task ........................................................................... 4-5
Visually Comparing Two Voltage Readings .................................................. 4-6
Communicating with an Instrument .............................................................................. 4-6
Selecting an Instrument................................................................................... 4-7
Acquiring and Parsing Information for an Instrument.................................... 4-7
Summary........................................................................................................................ 4-8
DAQ Assistant Express VI ............................................................................. 4-8
Tasks ............................................................................................................... 4-9
Instrument I/O Assistant Express VI .............................................................. 4-9
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Chapter 5
Using Other LabVIEW Features
All Controls and Indicators............................................................................................5-1
All VIs and Functions ....................................................................................................5-2
VIs ...................................................................................................................5-2
Functions .........................................................................................................5-2
Data Types .....................................................................................................................5-3
Dynamic Data Type.........................................................................................5-3
When to Use Other LabVIEW Features ........................................................................5-4
Appendix A
Technical Support and Professional Services
Glossary
Index
© National Instruments Corporation
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About This Manual
Use this manual as a tutorial to familiarize yourself with the LabVIEW
graphical programming environment and the basic LabVIEW features you
use to build data acquisition and instrument control applications.
This manual contains exercises that you can use to learn how to develop
basic applications in LabVIEW. These exercises take a short amount of
time to complete and help you get started with LabVIEW.
The end of each chapter includes a summary of the main concepts taught in
that chapter. Use these summaries to review what you learned.
Conventions
The following conventions appear in this manual:
»
The » symbol leads you through nested menu items and dialog box options
to a final action. The sequence File»Page Setup»Options directs you to
pull down the File menu, select the Page Setup item, and select Options
from the last dialog box.
This icon denotes a tip, which alerts you to advisory information.
This icon denotes a note, which alerts you to important information.
bold
Bold text denotes items that you must select or click in the software, such
as menu items and dialog box options. Bold text also denotes parameter
names, controls and indicators on the front panel, window names, dialog
boxes, sections of dialog boxes, menu names, and palette names.
italic
Italic text denotes variables, emphasis, a cross reference, or an introduction
to a key concept. Italic font also denotes text that is a placeholder for a word
or value that you must supply.
monospace
Text in this font denotes text or characters that you should enter from the
keyboard, sections of code, programming examples, and syntax examples.
This font is also used for the proper names of disk drives, paths, directories,
programs, subprograms, subroutines, device names, operations, variables,
filenames and extensions, and code excerpts.
© National Instruments Corporation
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About This Manual
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 <Command>-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:
Getting Started with LabVIEW
•
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 this help file to access information about
LabVIEW programming concepts, step-by-step instructions for using
LabVIEW, and reference information about LabVIEW VIs, functions,
palettes, menus, and tools. 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.
x
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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. When 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.
© National Instruments Corporation
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Figure 1-1. Front Panel of the Acquiring a Signal VI
Launching LabVIEW
The Getting Started window, shown in Figure 1-2, appears when you
launch LabVIEW. Use this window to create new VIs, select among the
most recently opened LabVIEW files, find examples, and launch the
LabVIEW Help. You also can access information and resources to help you
learn about LabVIEW, such as specific manuals, help topics, and resources
on the National Instruments Web site, ni.com.
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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 appears when you close all
open front panels and block diagrams. You also can display the window 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.
2.
In the Getting Started window, click the New or VI from Template
link to display the New dialog box.
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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.
Getting Started with LabVIEW
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 the template.
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Examine the front panel of the VI.
The user interface, or front panel, appears with a gray background and
includes controls and indicators. The title bar of the front panel
indicates that this window is the front panel for the Generate and
Display VI.
Note If the front panel is not visible, you can display the front panel by selecting
Window»Show Front Panel.
6.
Select Window»Show Block Diagram and examine the block
diagram of the VI.
The block diagram appears with a white background and includes VIs
and structures that control the front panel objects. The title bar of the
block diagram indicates that this window is the block diagram for the
Generate and Display VI.
7.
On the front panel toolbar, click the Run button, shown at left. You
also can press the <Ctrl-R> keys to run a VI.
Note The <Ctrl> key in keyboard shortcuts corresponds to the (Mac OS) <Option> or
<Command> key or (Linux) <Alt> key.
A sine wave appears on the graph on the front panel.
8.
Stop the VI by clicking the STOP button, shown at left, on the front
panel.
Adding a Control to the Front Panel
Controls on the front panel simulate the input mechanisms on a physical
instrument and supply data to the block diagram of the VI. Many physical
instruments have knobs you can turn to change an input value.
Complete the following steps to add a knob control to the front panel.
Throughout these exercises, you can undo recent edits by selecting Edit»Undo or
pressing the <Ctrl-Z> keys.
Tip
1.
© National Instruments Corporation
If the Controls palette, shown in Figure 1-4, is not visible on the front
panel, select View»Controls Palette to display it. The Controls
palette opens with the Express subpalette visible by default. If you
have selected another subpalette, you can return to the Express
subpalette by clicking Express on the Controls palette.
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Figure 1-4. Controls Palette
2.
Move the cursor over the icons on the Controls palette 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.
3.
Click the Numeric Controls icon to display the Numeric Controls
palette.
4.
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.
5.
Select File»Save As and save the VI as Acquiring a Signal.vi in
an easily accessible location.
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.
Getting Started with LabVIEW
Display the block diagram by pressing the <Ctrl-E> keys or by clicking
the block diagram. Pressing the <Ctrl-E> keys switches from the front
panel to the block diagram or from the block diagram to the front
panel.
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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 <Control>-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.
Figure 1-5. Configure Simulate Signal Dialog Box
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4.
Click the OK button to save the current configuration and close the
Configure Simulate Signal dialog box.
5.
Move the cursor over the down arrows at the bottom of the Simulate
Signal Express VI. The down arrows indicate you can reveal hidden
content by extending the border of the Express VI.
6.
When a double-headed arrow appears, shown at left, click and drag the
border of the Express VI to add two rows. When you release the border,
the Amplitude input appears.
Because the Amplitude input appears on the block diagram, you can
configure the amplitude of the sawtooth wave on the block diagram.
In Figure 1-5, notice that Amplitude is an option in the Configure
Simulate Signal dialog box. When inputs, such as Amplitude, appear
on the block diagram and in the configuration dialog box, you can
configure the inputs in either location.
Wiring Objects on the Block Diagram
To use the knob control 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
structure, 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. You must deselect an object to switch from using the
Positioning tool with the object to another 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.
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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.
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 control.
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. 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 VIs with a stop button to avoid this problem.
© National Instruments Corporation
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Modifying a Signal
Complete the following steps to add scaling to the signal and display the
results in the graph on the front panel.
1.
On the block diagram, use the Positioning tool to double-click the wire
that connects the Simulate Signal Express VI to the Waveform Graph
terminal, shown at left.
2.
Press the <Delete> key to delete this wire.
3.
If the Functions palette, shown in Figure 1-6, is not visible, select
View»Functions Palette to display it. The Functions palette opens
with the Express subpalette visible by default. If you have selected
another subpalette, you can return to the Express subpalette by
clicking Express on the Functions palette.
Figure 1-6. Functions Palette
4.
On the Arithmetic & Comparison palette, select the Scaling and
Mapping Express VI, shown at left, and place it on the block diagram
inside the loop between the Simulate Signal Express VI and the
Waveform Graph terminal. You can move the Waveform Graph
terminal to the right to make more room between the Express VI and
the terminal.
Note The Scaling and Mapping Express VI is available only in the LabVIEW Full and
Professional Development Systems. If you are using the Base Package, skip to the next
section.
The Configure Scaling and Mapping dialog box opens when you
place the Express VI on the block diagram.
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Define the value of the scaling factor by entering 10 in the Slope (m)
text box.
The Configure Scaling and Mapping dialog box should appear
similar to Figure 1-7.
Figure 1-7. Configure Scaling and Mapping Dialog Box
6.
Click the OK button to save the current configuration and close the
Configure Scaling and Mapping dialog box.
7.
Move the cursor over the arrow on the Sawtooth output of the
Simulate Signal Express VI.
8.
When the Wiring tool appears, click the arrow on the Sawtooth output
and then click the arrow on the Signals input of the Scaling and
Mapping Express VI, shown at left, to wire the two objects together.
© National Instruments Corporation
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9.
Use the Wiring tool to wire the Scaled Signals output of the Scaling
and Mapping Express VI to the Waveform Graph terminal.
Examine the wires connecting the Express VIs and terminals. The
arrows on the Express VIs and terminals indicate the direction that the
data flows along these wires. The block diagram should appear similar
to Figure 1-8.
Figure 1-8. Block Diagram of the Acquiring a Signal VI
10. Press the <Ctrl-S> keys or select File»Save to save the VI.
Displaying Two Signals on a Graph
To compare the signal generated by the Simulate Signal Express VI and the
signal modified by the Scaling and Mapping Express VI on the same graph,
use the Merge Signals function.
Complete the following steps to display two signals on the same graph.
1.
On the block diagram, move the cursor over the arrow on the Sawtooth
output of the Simulate Signal Express VI.
2.
Use the Wiring tool to wire the Sawtooth output to the Waveform
Graph terminal.
The Merge Signals function, shown at left, appears where the two
wires connect. A function is a built-in execution element, comparable
to an operator, function, or statement in a text-based programming
language. The Merge Signals function takes the two separate signals
and combines them so that both can display on the same graph.
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The block diagram should appear similar to Figure 1-9.
Figure 1-9. Block Diagram Showing the Merge Signals Function
3.
Press the <Ctrl-S> keys or select File»Save to save the VI.
4.
Return to the front panel, run the VI, and turn the knob control.
The graph plots the sawtooth wave and the scaled signal. The
maximum value on the y-axis automatically changes to be 10 times the
knob value. This scaling occurs because you set the slope to 10 in the
Scaling and Mapping Express VI.
5.
Click the STOP button to stop the VI.
Customizing a Knob Control
The knob control changes the amplitude of the sawtooth wave, so labeling
it Amplitude accurately describes the behavior of the knob.
Complete the following steps to customize the appearance of the knob
control.
1.
On the front panel, right-click the knob and select Properties from the
shortcut menu to display the Knob Properties dialog box.
2.
In the Label section on the Appearance page, delete the label Knob,
and enter Amplitude in the text box.
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The Knob Properties dialog box should appear similar to Figure 1-10.
Figure 1-10. Knob Properties Dialog Box
3.
Click the Scale tab and in the Scale Style section, place a checkmark
in the Show color ramp checkbox.
The knob on the front panel updates to reflect these changes.
Getting Started with LabVIEW
4.
Click the OK button to save the current configuration and close the
Knob Properties dialog box.
5.
Save the VI.
6.
Reopen the Knob Properties dialog box and experiment with other
properties of the knob. For example, on the Scale page, try changing
the colors for the Marker text color by clicking the color box.
7.
Click the Cancel button to avoid applying any changes you made
while experimenting. If you want to keep the changes you made, click
the OK button.
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Customizing a Waveform Graph
The waveform graph indicator displays the two signals. To indicate which
plot is the scaled signal and which is the simulated signal, you can
customize the plots.
Complete the following steps to customize the appearance of the waveform
graph indicator.
1.
On the front panel, move the cursor over the top of the plot legend on
the waveform graph.
Though the graph has two plots, the plot legend displays only one plot.
2.
When a double-headed arrow appears, shown in Figure 1-11, click and
drag the border of the plot legend until the second plot name appears.
Figure 1-11. Expanding a Plot Legend
3.
Right-click the waveform graph and select Properties from the
shortcut menu to display the Waveform Graph Properties dialog
box.
4.
On the Plots page, select Sawtooth from the pull-down menu. In the
Colors section, click the Line color box to display the color picker.
Select a new line color.
5.
Select Sawtooth (Scaled) from the pull-down menu.
6.
Place a checkmark in the Do not use waveform names for plot names
checkbox.
7.
In the Name text box, delete the current label and change the name of
this plot to Scaled Sawtooth.
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8.
Click the OK button to save the current configuration and close the
Waveform Graph Properties dialog box.
The plot color on the front panel changes.
9.
Reopen the Waveform Graph Properties dialog box and experiment
with other properties of the graph. For example, on the Scales page, try
disabling automatic scaling and changing the minimum and maximum
value of the y-axis.
10. Click the Cancel button to avoid applying any changes you made
while experimenting. If you want to keep the changes you made, click
the OK button.
11. Save and close the VI.
Summary
The following topics are a summary of the main concepts you learned in
this chapter.
New Dialog Box and Template VIs
The New dialog box contains many template VIs, including the ones used
in this manual. The template VIs help you start building VIs for common
measurements and other tasks. The template VIs include the Express VIs,
functions, and front panel objects you need to get started building common
measurement applications.
Use one of the following methods to access the New dialog box:
•
Click the New, VI from Template, or More links in the Getting
Started window after you start LabVIEW.
•
Select File»New from the menu bar of the Getting Started window,
the front panel, or the block diagram.
Front Panel
The front panel is the user interface of a VI. You build the front panel by
using controls and indicators, which are the interactive input and output
terminals of the VI, respectively. Controls and indicators are located on the
Controls palette.
Controls are knobs, push buttons, dials, and other input mechanisms.
Controls simulate instrument input mechanisms and supply data to the
block diagram of the VI.
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Indicators are graphs, LEDs, and other displays. Indicators simulate
instrument output mechanisms and display data the block diagram acquires
or generates.
Property Dialog Boxes
Use property dialog boxes or shortcut menus to configure how controls and
indicators appear or behave on the front panel. Right-click a control or
indicator on the front panel and select Properties from the shortcut menu
to access the property dialog box for that object. You cannot access
property dialog boxes for a control or indicator when a VI is running.
Block Diagram
The block diagram contains the graphical source code, also known as G
code or block diagram code, for how the VI runs. The block diagram code
uses graphical representations of functions to control the front panel
objects. Front panel objects appear as icon terminals on the block diagram.
Wires connect control and indicator terminals to Express VIs, VIs, and
functions. Data flows through the wires from controls to VIs and functions,
from VIs and functions to other VIs and functions, and from VIs and
functions to indicators. The movement of data through the nodes on the
block diagram determines the execution order of the VIs and functions.
This movement of data is known as dataflow programming.
Express VIs
Use Express VIs located on the Functions palette for common
measurement tasks. When you place an Express VI on the block diagram,
the dialog box you use to configure that Express VI appears by default. Set
the options in this configuration dialog box to specify how the Express VI
behaves. You also can double-click an Express VI or right-click an Express
VI and select Properties from the shortcut menu to display the
configuration 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.
Express VIs appear on the block diagram as expandable nodes with icons
surrounded by a blue field. You can resize an Express VI to display its
inputs and outputs. The inputs and outputs you can display for the Express
VI depend on how you configure the VI.
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2
Analyzing and Saving a Signal
LabVIEW includes a set of Express VIs that help you analyze signals. This
chapter teaches you how to use LabVIEW to perform a basic analysis of a
signal and how to save the analyzed data to a file.
Building a VI from a Template
In the following exercises, you will build a VI that generates a signal,
extracts the DC value of the signal, indicates if the signal exceeds a certain
limit, and records the data. When you complete the exercises, the front
panel of the VI will look similar to the front panel in Figure 2-1.
You can complete the exercises in this chapter in approximately 40 minutes.
Figure 2-1. Front Panel of the Warning Light VI
Opening a New VI from a Template
To build this VI, you can start from the New dialog box.
Complete the following steps to select a new template VI that generates,
analyzes, and displays a signal.
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Tip
1.
In the Getting Started window, click the New link to display the New
dialog box.
2.
From the Create New list, select VI»From Template»Tutorial
(Getting Started)»Generate, Analyze, and Display. This template
VI simulates a signal and analyzes it for its root mean square (RMS)
value.
3.
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 the template.
4.
If the Context Help window, shown in Figure 2-2, is not visible, select
Help»Show Context Help from the front panel or block diagram
menu bar to display the Context Help window.
You also can press the <Ctrl-H> keys to display the Context Help window.
Figure 2-2. Context Help Window
5.
Display the block diagram by pressing the <Ctrl-E> keys.
6.
Move the cursor over the Amplitude and Level Measurements Express
VI, shown at left.
When you move the cursor over the Express VI, the Context Help
window displays information about the Express VI, including
information about how it is configured.
Keep the Context Help window open. It will provide useful
information as you complete the rest of this exercise.
Note The Amplitude and Level Measurements Express VI is available only in the
LabVIEW Full and Professional Development Systems. If you are using the Base Package,
skip the Analyzing the Amplitude of a Signal section.
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Modifying the Block Diagram
The Simulate Signal Express VI simulates a sine wave by default. You can
customize the simulated signal by changing the options in the Configure
Simulate Signal dialog box.
Complete the following steps to change the simulated signal from a sine
wave to a DC signal with uniform white noise.
1.
On the block diagram, right-click the Simulate Signal Express VI and
select Properties from the shortcut menu to display the Configure
Simulate Signal dialog box.
2.
Select DC from the Signal type pull-down menu.
3.
Place a checkmark in the Add noise checkbox to add noise to the DC
signal.
4.
Enter 0.1 in the Noise amplitude text box.
The Result Preview section displays a random signal. The Configure
Simulate Signal dialog box should appear similar to Figure 2-3.
Figure 2-3. Configure Simulate Signal Dialog Box
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5.
Click the OK button to save the current configuration and close
the Configure Simulate Signal dialog box.
6.
Display the front panel by pressing the <Ctrl-E> keys.
7.
Run the VI.
The signal appears in the graph and the RMS value for the signal
appears in the numeric indicator.
8.
Click the STOP button to stop the VI.
9.
Select File»Save As and save the VI as Analysis.vi in an easily
accessible location.
Modifying the Front Panel
If a template VI contains an indicator you do not want to use, you can delete
it.
Complete the following steps to remove the RMS indicator from the front
panel.
1.
On the front panel, move the cursor over the RMS indicator until the
Positioning tool appears.
2.
Click the RMS indicator, shown at left, to select it and press the
<Delete> key.
3.
Display the block diagram.
A wire appears as a dashed black line with a red X in the middle, shown
at left. This is a broken wire. The Run button, shown at left, appears
broken to indicate the VI cannot run.
4.
Click the broken Run button to display the Error list window.
The Error list window lists all errors in the VI and provides details
about each error. You can use the Error list window to locate errors.
Click the Help button for more information about the error.
5.
In the errors and warnings field, double-click the Wire: has loose
ends error to highlight the broken wire.
LabVIEW displays the problem causing the error.
6.
Press the <Ctrl-B> keys to delete the broken wire.
Pressing the <Ctrl-B> keys deletes all broken wires on the block
diagram. You can press the <Delete> key to delete only the selected
broken wire.
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Select View»Error List to display the Error list window. No errors
appear in the errors and warnings field.
Note You also can press the <Ctrl-L> keys to display the Error list window.
8.
Click the Close button to close the Error list window.
The Run button no longer appears broken.
Analyzing the Amplitude of a Signal
The Amplitude and Level Measurements Express VI includes options that
you can use to analyze the voltage characteristics of a signal.
Complete the following steps to reconfigure the Express VI to measure the
peak-to-peak amplitude values of the signal.
1.
On the block diagram, right-click the Amplitude and Level
Measurements Express VI and select Properties from the shortcut
menu to display the Configure Amplitude and Level Measurements
dialog box.
You also can double-click the Express VI to display the Configure Amplitude and
Level Measurements dialog box.
Tip
2.
In the Amplitude Measurements section, remove the checkmark
from the RMS checkbox.
3.
Click the Help button, shown at left, in the bottom right corner of the
Configure Amplitude and Level Measurements dialog box to
display the LabVIEW Help topic for this Express VI.
You also can click the Detailed help link in the Context Help window
to display the LabVIEW Help topic for this Express VI.
The Amplitude and Level Measurements help topic describes the
Express VI, the inputs and outputs of the Express VI, and the
configuration dialog box options. Each Express VI has a
corresponding help topic you can access by clicking the Help button.
4.
In the Amplitude and Level Measurements topic, find the output
parameter whose description indicates that it takes a measurement
from the most positive peak to the most negative peak of the signal.
5.
Minimize the LabVIEW Help to return to the Configure Amplitude
and Level Measurements dialog box.
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6.
Select the input or output you decided to use.
The option you selected, Peak to peak, appears in the Results section
with the corresponding value of the measurement.
7.
Click the OK button to save the current configuration and close
the Configure Amplitude and Level Measurements dialog box.
The RMS output of the Amplitude and Level Measurements Express
VI changes to reflect the new Peak to Peak parameter, shown at left.
Adding a Warning Light
If you want a visual cue indicating when a value exceeds a specified limit,
use a warning light.
Complete the following steps to add a warning light to the VI.
1.
On the front panel, display the Controls palette by selecting View»
Controls Palette.
Note You also can right-click any blank space on the front panel or the block diagram to
display the Controls or Functions palettes.
2.
On the Express palette, select the LEDs palette, shown in Figure 2-4.
Figure 2-4. LEDs Palette
3.
Select the round LED indicator and place it on the front panel to the
left of the waveform graph.
4.
Double-click the Boolean label above the LED and enter Warning to
change the label of the LED. You also can change the label on the
Appearance page of the Boolean Properties dialog box.
You will use this LED in a later exercise to indicate when a value has
exceeded its limit.
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5.
Select File»Save As to display the Save As dialog box.
6.
Read the various dialog box options. Select the Copy and Substitute
copy for original radio buttons to create a copy of the original VI and
immediately edit the copy.
7.
Click the Continue button and save the VI as Warning Light.vi in
an easily accessible location.
Setting a Warning Level Limit
To specify the value at which you want the warning light to turn on, use the
Comparison Express VI.
Complete the following steps to compare the peak-to-peak value to a limit
you set.
1.
On the block diagram, display the Functions palette by selecting
View»Functions Palette.
2.
Click the Search button, shown at left, on the Functions palette, and
enter Comparison in the text box. LabVIEW searches as you type and
displays any matches in the search results text box. LabVIEW displays
a folder glyph to the left of subpalettes in the search results and
displays a light blue glyph to the left of Express VIs in the search
results.
3.
Double-click Comparison <<Express Comparison>> to display the
Express Comparison subpalette and temporarily highlight the
Comparison Express VI on the subpalette.
4.
Select the Comparison Express VI on the Express Comparison
palette and place it to the right of the Amplitude and Level
Measurements Express VI. The Configure Comparison dialog box
appears.
5.
In the Compare Condition section, select the > Greater option.
6.
In the Comparison Inputs section, select Value and enter 0.195 in
the Value text box to assign a constant value at which you want the
warning light to turn on.
7.
Click the OK button to save the current configuration and close
the Configure Comparison dialog box.
The name of the Comparison Express VI changes to reflect the
operation of the Express VI, shown at left. Greater indicates that the
Express VI does a greater than comparison.
8.
© National Instruments Corporation
Wire the Peak to Peak output of the Amplitude and Level
Measurements Express VI to the Operand 1 input of the Greater
Express VI.
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9.
Move the cursor over the wire that connects the Peak to Peak output
to the Operand 1 input.
10. When the Positioning tool appears, right-click the wire that connects
the Peak to Peak output to the Operand 1 input and select Create»
Numeric Indicator from the shortcut menu.
A Peak to Peak terminal, shown at left, appears on the block diagram.
If the Peak to Peak terminal appears to be on top of the wires between
the Express VIs, move the Express VIs and Peak to Peak terminal
around to create more space. For example, move the Peak to Peak
terminal into blank space above the Express VIs.
Warning the User
After you specify the values at which you want the warning light to turn on,
you must wire the warning light to the Greater Express VI.
Complete the following steps to provide a visual cue when the peak-to-peak
value of the signal exceeds a specified limit.
1.
On the block diagram, move the Warning terminal to the right of the
Greater Express VI. Make sure the Warning terminal is inside the gray
loop, as shown in Figure 2-5.
Figure 2-5. Block Diagram of the Warning Light VI
2.
Wire the Result output of the Greater Express VI to the Warning
terminal.
The block diagram should appear similar to Figure 2-5.
3.
Display the front panel.
A numeric indicator labeled Peak to Peak also appears on the front
panel. This indicator displays the peak-to-peak value of the signal.
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Run the VI.
When the peak-to-peak value exceeds 0.195, the Warning indicator
lights.
5.
Click the STOP button to stop the VI.
6.
Select File»Save to save the VI.
Configuring a VI to Save Data to a File
To store information about the data a VI generates, use the Write To
Measurement File Express VI.
Complete the following steps to build a VI that saves peak-to-peak values
and other information to a LabVIEW data file.
1.
On the block diagram, select the Write To Measurement File Express
VI from the Output palette and place it on the block diagram below
and to the right of the Amplitude and Level Measurements Express VI.
The Configure Write To Measurement File dialog box opens when
you place the Express VI on the block diagram.
The File Name text box displays the full path to the output file,
test.lvm. A .lvm file is a tab-delimited text measurement file you
can open with a spreadsheet application or a text-editing application.
LabVIEW saves data with up to six digits of precision in a .lvm file.
LabVIEW places the .lvm file in the default LabVIEW Data
directory. LabVIEW installs the LabVIEW Data directory in the
default file directory of the operating system.
When you want to view the data, use the file path displayed in the File
Name text box to access the test.lvm file.
2.
In the If a file already exists section of the Configure Write To
Measurement File dialog box, select the Append to file option.
If you select Append to file, LabVIEW writes all the data to the
test.lvm file without erasing any existing data in the file.
3.
In the Segment Headers section, select the One header only option
to create only one header in the file to which LabVIEW writes the data.
4.
Enter the following text in the File Description text box: Sample of
peak to peak values. LabVIEW appends the text you enter in this
text box to the header of the file.
5.
© National Instruments Corporation
Click the OK button to save the current configuration and close
the Configure Write To Measurement File dialog box.
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Saving Data to a File
When you run the VI, LabVIEW saves the data to the test.lvm file.
Complete the following steps to generate the test.lvm file.
1.
On the block diagram, wire the Peak to Peak output of the Amplitude
and Level Measurements Express VI to the Signals input of the Write
To Measurement File Express VI.
2.
Select File»Save As and save the VI as Save Data.vi in an easily
accessible location.
3.
Display the front panel and run the VI.
4.
Click the STOP button on the front panel.
5.
To view the data you saved, open the test.lvm file with a spreadsheet
or text-editing application.
The file has one header, which contains information about the
Express VI.
6.
Close the file when you finish looking at it and return to the Save
Data VI.
Adding a Button That Stores Data When Pressed
If you want to store only certain data points, you can configure the Write
To Measurement File Express VI to save peak-to-peak values only when a
user clicks a button.
Complete the following steps to add a button to the VI and configure how
the button responds when a user clicks it.
1.
Click the Search button on the Controls palette, enter button in the
text box, and select Buttons & Switches from the list of controls.
2.
Select the rocker button on the Buttons & Switches palette and place
it to the right of the waveform graph.
3.
Right-click the rocker button and select Properties from the shortcut
menu to display the Boolean Properties dialog box.
4.
Change the label of the button to Write to File.
5.
On the Operation page of the Boolean Properties dialog box, select
Latch when pressed from the Button behavior list.
Use the Operation page to specify how a button behaves when a user
clicks it. To see how the button reacts to a click, click the button in the
Preview Selected Behavior section.
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6.
Click the OK button to save the current configuration and close
the Boolean Properties dialog box.
7.
Save the VI.
Saving Data When Prompted by a User
Complete the following steps to build a VI that logs data to a file when the
user clicks a button on the front panel.
1.
On the block diagram, double-click the Write To Measurement File
Express VI to display the Configure Write To Measurement File
dialog box.
2.
Change the filename test.lvm in the File name text box to
Selected Samples.lvm to save the data to a different file.
3.
Click the OK button to save the current configuration and close
the Configure Write To Measurement File dialog box.
4.
Right-click the Signals input of the Write To Measurement File
Express VI and select Insert Input/Output from the shortcut menu to
insert the Comment input.
In the previous exercise you learned to add inputs and outputs by
expanding the Express VI using the down arrows. This method is a
different way of displaying and selecting the inputs and outputs of an
Express VI.
The inputs and outputs of an Express VI appear in a predetermined
order when you add new inputs and outputs. To select a specific input,
you might need to add an input first, then change the input to the
specific one you want to use by right-clicking the input and selecting
Select Input/Output from the shortcut menu.
5.
Right-click the Comment input of the Write To Measurement File
Express VI and select Select Input/Output»Enable from the shortcut
menu to insert the Enable input.
6.
Move the Write to File terminal to the left of the Write To
Measurement File Express VI.
7.
Wire the Write to File terminal to the Enable input of the Write To
Measurement File Express VI.
The block diagram should appear similar to Figure 2-6.
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Figure 2-6. Block Diagram of the Save Data VI
Viewing Saved Data
Complete the following steps to view the data that you save to the
Selected Samples.lvm file.
1.
Display the front panel and run the VI. Click the Write to File button
several times.
2.
Click the STOP button on the front panel.
3.
Open the Selected Samples.lvm file with a spreadsheet or
text-editing application.
The Selected Samples.lvm file differs from the test.lvm file.
test.lvm recorded all the data generated by the Save Data VI,
whereas Selected Samples.lvm recorded data only when you
clicked the Write to File button.
4.
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Save and close the VI.
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Summary
The following topics are a summary of the main concepts you learned in
this chapter.
LabVIEW Documentation Resources
LabVIEW includes extensive documentation for new and experienced
LabVIEW users. Documentation resources include the Context Help
window, the LabVIEW Help, examples, and manuals.
The Context Help window displays basic information about LabVIEW
objects when you move the cursor over each object. To access the Context
Help window, select Help»Show Context Help or press the <Ctrl-H>
keys.
The LabVIEW Help contains information about LabVIEW programming
concepts, step-by-step instructions for using LabVIEW, and reference
information about LabVIEW VIs, functions, palettes, menus, and tools. To
access help information for Express VIs, click the Help button, shown at
left, in the configuration dialog box while configuring an Express VI. You
also can access the LabVIEW Help by clicking the Detailed help link in the
Context Help window, by right-clicking a VI or function on the block
diagram or on a pinned palette and selecting Help from the shortcut menu,
or by selecting Help»Search the LabVIEW Help.
Controls and Indicators
You can configure the controls and indicators on the front panel to perform
tasks depending on what you want a VI to do. In this chapter, you learned
to use controls and indicators in the following ways:
•
You can build VIs that perform a task when certain conditions occur,
such as displaying a warning light when a value exceeds a certain limit.
•
You can build VIs that let users control when an Express VI executes
by using buttons and the Enable input. You can configure the buttons
to operate in one of six ways using the Operation page of the Boolean
Properties dialog box.
Saving Data
The Write To Measurement File Express VI saves data that a VI generates
and analyzes to a .lvm or .tdm measurement file. The text-based
measurement file (.lvm) is a tab-delimited text file you can open with a
spreadsheet application or a text-editing application. LabVIEW saves data
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with up to six digits of precision in a .lvm file. In addition to the data an
Express VI generates, the .lvm file includes headers that contain
information about the data, such as the date and time LabVIEW generated
the data. The binary measurement file (.tdm) is a binary file that contains
waveform data. Binary .tdm files provide higher accuracy for
floating-point numbers, have a smaller disk footprint, and perform faster
than text-based measurement files (.lvm).
LabVIEW installs the LabVIEW Data directory in the default file directory
of the operating system to help you organize and locate the data files
LabVIEW generates. Refer to the LabVIEW Help for more information
about saving data to and retrieving data from .lvm and .tdm files.
Errors and Broken Wires
The Run button appears broken when the VI you are creating or editing
contains errors. If the Run button is still broken when you finish wiring the
block diagram, the VI is broken and cannot run.
Click the broken Run button or select View»Error List to find out why a
VI is broken. You can use the Error list window to locate errors. Click the
Help button for more information about the error. Double-click the error in
the errors and warnings field to highlight the problem causing the error.
A broken wire appears as a dashed black line with a red X in the middle.
Broken wires occur for a variety of reasons, such as if you delete wired
objects. The VI cannot run if the block diagram contains broken wires.
Move the Wiring tool over a broken wire to display a tip strip that describes
why the wire is broken. This information also appears in the Context Help
window when you move the Wiring tool over a broken wire. Right-click the
wire and select List Errors from the shortcut menu to display the Error
list window. Click the Help button for more information about why the
wire is broken.
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Customizing a VI
You can choose one of many LabVIEW template VIs to use as a starting
point when building VIs. However, sometimes you need to build a VI for
which a template is not available. This chapter teaches you how to build
and customize a VI without using a template.
Building a VI from a Blank VI
In the following exercises, you will open a blank VI and add Express VIs
and structures to the block diagram to build a new VI. You will build a VI
that generates a signal, reduces the number of samples in the signal, and
displays the resulting data in a table on the front panel. When you complete
the exercises, the front panel of the VI will look similar to the front panel
in Figure 3-1.
You can complete the exercises in this chapter in approximately 30 minutes.
Figure 3-1. Front Panel of the Reduce Samples VI
Opening a Blank VI
If no template is available for the VI you want to build, you can start with
a blank VI and add Express VIs to accomplish a specific task.
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Customizing a VI
Complete the following steps to open a blank VI.
1.
In the Getting Started window, click the Blank VI link in the New
section or press the <Ctrl-N> keys to open a blank VI.
A blank front panel and block diagram appear.
Note You also can open a blank VI by selecting File»New VI or by selecting File»New
and selecting Blank VI from the Create New list.
2.
If the Functions palette is not visible, right-click any blank space on
the block diagram to display a temporary version of the Functions
palette. Click the thumbtack, shown at left, in the upper left corner of
the Functions palette to pin the palette so it is no longer temporary.
Adding an Express VI That Simulates a Signal
Complete the following steps to find the Express VI you want to use and
add it to the block diagram.
1.
If the Context Help window is not visible, press the <Ctrl-H> keys to
display the window. You also can click the Show Context Help
Window button, shown at left, on the front panel or block diagram
toolbar to display the Context Help window.
2.
On the Functions palette, select the Express»Input palette and move
the cursor over the Express VIs on the Input palette.
The Context Help window displays information about the behavior of
each Express VI.
3.
Use the information that appears in the Context Help window to find
the Express VI that can generate a sine wave signal.
4.
Select the Express VI and place it on the block diagram. The
Configure Simulate Signal dialog box appears.
5.
Move the cursor over the various options in the Configure Simulate
Signal dialog box, such as Frequency (Hz), Amplitude, and Samples
per second (Hz). Read the information that appears in the Context
Help window.
6.
Configure the Simulate Signal Express VI to generate a sine wave with
a frequency of 10.7 and amplitude of 2.
The signal in the Result Preview window changes to reflect the
configured sine wave.
7.
Getting Started with LabVIEW
Click the OK button to save the current configuration and close the
Configure Simulate Signal dialog box.
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8.
Customizing a VI
Move the cursor over the Simulate Signal Express VI and read the
information that appears in the Context Help window.
The Context Help window now displays the configuration
information of the Simulate Signal Express VI.
9.
Save the VI as Reduce Samples.vi in an easily accessible location.
Searching the Help and Modifying a Signal
Complete the following steps to use the LabVIEW Help to search for the
Express VI that reduces the number of samples in a signal.
1.
Move the cursor over the Simulate Signal Express VI and click the
Detailed help link in the Context Help window to display the
Simulate Signal topic in the LabVIEW Help. You might have to enlarge
or scroll down in the Context Help window to see the Detailed help
link.
You also can access the LabVIEW Help by right-clicking a VI or
function on the block diagram or on a pinned palette and selecting
Help from the shortcut menu or by selecting Help»Search the
LabVIEW Help.
2.
Click the Search tab, enter sample compression in the Type in the
word(s) to search for text box, and press the <Enter> key. You can
place quotation marks around the phrase to search for the exact phrase.
For example,you can enter "sample compression" to narrow the
search results.
This word choice reflects what you want this Express VI to
do—compress, or reduce, the number of samples in a signal.
3.
Double-click the Sample Compression topic to display the topic that
describes the Sample Compression Express VI.
4.
After you read the description of the Express VI, click the square gray
Place on the block diagram button to place the Express VI on the
cursor.
5.
Move the cursor to the block diagram.
6.
Place the Sample Compression Express VI on the block diagram to the
right of the Simulate Signal Express VI.
7.
Configure the Sample Compression Express VI to reduce the signal by
a factor of 25 using the mean of these values.
8.
Click the OK button to save the current configuration and close the
Configure Sample Compression dialog box.
© National Instruments Corporation
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9.
Use the Wiring tool to wire the Sine output of the Simulate Signal
Express VI to the Signals input of the Sample Compression
Express VI.
Customizing a User Interface from the Block Diagram
In the previous exercises, you added controls and indicators to the front
panel using the Controls palette. You also can create controls and
indicators from the block diagram.
Complete the following steps to create controls and indicators from the
block diagram.
1.
On the block diagram, right-click the Mean output of the Sample
Compression Express VI and select Create»Numeric Indicator from
the shortcut menu to create a numeric indicator.
2.
Right-click the Mean output of the Sample Compression Express VI
and select Insert Input/Output from the shortcut menu to insert the
Enable input.
3.
Right-click the Enable input and select Create»Control from the
shortcut menu to create the Enable switch.
Control terminals have a thicker border than indicator terminals. Also,
an arrow appears on the right of the terminal if the terminal is a control,
and an arrow appears on the left of the terminal if the terminal is an
indicator.
4.
Right-click the wire that connects the Sine output of the Simulate
Signal Express VI to the Signals input of the Sample Compression
Express VI and select Create»Graph Indicator from the shortcut
menu.
5.
Use the Wiring tool to wire the Mean output of the Sample
Compression Express VI to the Sine graph indicator.
The Merge Signals function appears.
6.
Arrange the objects on the block diagram so they appear similar to
Figure 3-2.
You can right-click any wire and select Clean Up Wire from the shortcut menu to
have LabVIEW automatically find a route for the wire around existing objects on the block
diagram. LabVIEW also routes a wire to decrease the number of bends in the wire.
Tip
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Customizing a VI
Figure 3-2. Block Diagram of the Reduce Samples VI
7.
Display the front panel.
The controls and indicators you added appear on the front panel with
labels that correspond to the inputs and outputs from which you
created the controls and indicators.
8.
Save the VI.
Configuring a VI to Run Continuously until the User Stops It
In the current state, the VI runs once, generates one signal, then stops
executing. To run the VI until a condition occurs, you can use a While
Loop.
Complete the following steps to add a While Loop to the block diagram.
1.
Display the front panel and run the VI.
The VI runs once and then stops. The front panel does not have a stop
button.
2.
On the block diagram, select the While Loop on the Execution
Control palette.
3.
Move the cursor to the upper left corner of the block diagram. Click to
place the top left corner of the While Loop.
© National Instruments Corporation
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4.
Drag the cursor diagonally to enclose all the Express VIs and wires, as
shown in Figure 3-3.
Figure 3-3. Placing the While Loop around the Express VIs
The While Loop, shown at left, appears with a STOP button wired to
the conditional terminal. This While Loop is configured to stop when
the user clicks the STOP button.
5.
Display the front panel and run the VI.
The VI now runs until you click the STOP button. A While Loop
executes the VIs and functions inside the loop until the user clicks the
STOP button.
6.
Click the STOP button and save the VI.
Searching for Examples
To learn more about how you can use a certain VI, you can search for and
view an example that uses the VI.
Complete the following steps to find and open an example that uses the
Time Delay Express VI.
1.
Select Help»Search the LabVIEW Help to display the LabVIEW
Help.
2.
Click the Search tab, enter "time delay" in the Type in the word(s)
to search for text box, and press the <Enter> key.
Before you search, you can narrow the search results by placing a
checkmark in the Search titles only checkbox near the bottom of the
help window. You also can use operators such as AND, OR, and NEAR in
the Type in the word(s) to search for text box to narrow the search
results.
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3.
Click the Location column heading to sort the search results by
content type. Reference topics contain reference information about
block diagram objects such as VIs, functions, properties, and methods.
How-To topics contain step-by-step instructions for using LabVIEW.
Concept topics contain information about LabVIEW programming
concepts.
4.
Double-click the Time Delay topic to display the topic that describes
the Time Delay Express VI.
5.
After you read the description of the Express VI, click the Open
example button in the Example section near the bottom of the topic to
open an example that uses the Time Delay Express VI.
6.
Click the Browse related examples button to open the NI Example
Finder and display a list of other examples that use this VI. The NI
Example Finder searches among hundreds of example VIs, including
all installed examples and the examples located on NI Developer Zone
at ni.com/zone. You can modify an example VI to fit an application,
or you can copy and paste from one or more examples into a VI that
you create.
You also can select Help»Find Examples or click the Find Examples
link in the Examples section of the Getting Started window to launch
the NI Example Finder. You can right-click a VI or function on the
block diagram or on a pinned palette and select Examples from the
shortcut menu to display a help topic with links to examples for that VI
or function.
7.
After you experiment with the NI Example Finder and the example
VIs, close the NI Example Finder and the example VIs to return to the
Reduce Samples VI.
Controlling the Speed of Execution
To plot the points on the waveform graph more slowly, you can add a time
delay to the block diagram.
Complete the following steps to control the speed at which the VI runs.
1.
On the block diagram, search for the Time Delay Express VI on the
Functions palette and place it inside the While Loop.
2.
Enter 0.250 in the Time delay (seconds) text box.
This time delay specifies how fast the loop runs. With a 0.250 second
time delay, the loop iterates once every quarter of a second.
3.
© National Instruments Corporation
Click the OK button to save the current configuration and close the
Configure Time Delay dialog box.
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4.
Display the front panel and run the VI.
5.
Click the Enable switch and examine the change on the graph.
If the Enable switch is on, the graph displays the reduced signal. If the
Enable switch is off, the graph does not display the reduced signal.
6.
Click the STOP button to stop the VI.
Using a Table to Display Data
Complete the following steps to display a collection of mean values in a
table on the front panel.
1.
On the front panel, search for the Express Table indicator on the
Controls palette and place it on the front panel to the right of the
waveform graph.
2.
Display the block diagram.
LabVIEW wired the Table terminal to the Build Table Express VI.
3.
If the Build Table Express VI and the Table terminal are not selected
already, click an open area on the block diagram to the left of the Build
Table Express VI and the Table terminal. Drag the cursor diagonally
until the selection rectangle encloses the Build Table Express VI and
the Table terminal, shown at left.
A moving dashed outline, called a marquee, highlights the Build Table
Express VI, the Table terminal, and the wire joining the two.
4.
Drag the objects into the While Loop to the right of the Mean terminal.
The While Loop resizes to enclose the Build Table Express VI and the
Table terminal.
5.
Getting Started with LabVIEW
Use the Wiring tool to wire the Mean terminal of the Sample
Compression Express VI to the Signals input of the Build Table
Express VI.
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The block diagram should appear similar to Figure 3-4.
Figure 3-4. Block Diagram of the Reduce Samples VI
6.
Display the front panel and run the VI.
7.
Click the Enable switch.
The table displays the mean values of every 25 samples of the sine
wave. If the Enable switch is off, the table does not record the mean
values.
8.
Stop the VI.
9.
Experiment with properties of the table by using the Table Properties
dialog box. For example, try changing the number of columns to one.
10. Save and close the VI.
Summary
The following topics are a summary of the main concepts you learned in
this chapter.
Using the LabVIEW Help Resources
You can use the Context Help window and the LabVIEW Help to learn
more about Express VIs. Both provide information that describe the
functionality of the Express VI and how to configure the Express VI.
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In this chapter, you learned to use the help resources in the following ways:
•
The Context Help window displays basic information about
LabVIEW objects when you move the cursor over each object. Objects
with context help information include VIs, structures, palettes, dialog
box components, and so on.
•
When you move the cursor over an Express VI on the block diagram,
the Context Help window displays a brief description of the Express
VI and information about how you configured the Express VI.
•
If you find an Express VI or other block diagram object in the
LabVIEW Help you want to use, you can click a Place on the block
diagram button to place the object on the block diagram.
•
To navigate the LabVIEW Help, use the Contents, Index, and Search
tabs. Use the Contents tab to get an overview of the topics and
structure of the help. Use the Index tab to find a topic by keyword.
Use the Search tab to search the help for a word or phrase.
•
On the Search tab of the LabVIEW Help, use operators such as AND,
OR, and NEAR to narrow the search results. To search for an exact
phrase, place quotation marks around the phrase. Before you search,
you also can narrow the search results by placing a checkmark in the
Search titles only checkbox near the bottom of the help window.
•
On the Search tab of the LabVIEW Help, you can click the Location
column heading above the list of search results to sort the results by
content type. Reference topics contain reference information about
block diagram objects such as VIs, functions, properties, and methods.
How-To topics contain step-by-step instructions for using LabVIEW.
Concept topics contain information about LabVIEW programming
concepts.
Customizing the Block Diagram Code
You can use many controls, indicators, Express VIs, and structures to build
a VI. To customize a VI, you can create controls and indicators, control
when a VI stops running, and display generated data in a table.
Creating Controls and Indicators
Create controls and indicators on the block diagram by right-clicking the
Express VI input, output, or wire, selecting Create from the shortcut menu,
and selecting among the available options. LabVIEW wires the control or
indicator you created to the input, output, or wire you right-clicked.
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Control terminals have a thicker border than indicator terminals. Also, an
arrow appears on the right of the terminal if the terminal is a control, and
an arrow appears on the left of the terminal if the terminal is an indicator.
Controlling When a VI Stops Running
Use a While Loop to run the code enclosed within the loop continually. A
While Loop stops running when a stop condition occurs. When you place
or move an object in a While Loop near the border, the loop resizes to add
space for that object.
The Execution Control palette includes objects you can use to control the
number of times a VI runs, as well as the speed at which the VI runs.
Displaying Data in a Table
The table indicator displays generated data. Use the Build Table Express VI
to build a table of generated data.
© National Instruments Corporation
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4
Optional: Acquiring Data and
Communicating with
Instruments
This chapter introduces you to the Express VIs you use to acquire data and
communicate with instruments on Windows. These exercises require data
acquisition hardware.
Refer to the Taking Measurements book on the Contents tab in the
LabVIEW Help for information about acquiring data and communicating
with instruments on all platforms.
Acquiring a Signal
In the following exercises, you will use the DAQ Assistant Express VI to
create a task in NI-DAQmx. NI-DAQmx is a programming interface you
can use to communicate with data acquisition devices. Refer to the Getting
Started»Taking an NI-DAQmx Measurement in LabVIEW book on
the Contents tab in the LabVIEW Help for information about additional
methods you can use to create NI-DAQmx tasks.
Note The following exercises require that you have NI-DAQmx and an
NI-DAQmx-supported device. Refer to the National Instruments Web site at ni.com/daq
for the list of NI-DAQmx-supported devices. If you do not have NI-DAQmx or an
NI-DAQmx-supported device, refer to the Taking Measurements book on the Contents
tab in the LabVIEW Help for information about using Traditional NI-DAQ (Legacy) for
data acquisition.
In the following exercises, you will create an NI-DAQmx task that
continuously takes a voltage reading and plots the data on a waveform
graph.
You can complete the exercises in this chapter in approximately 30 minutes.
© National Instruments Corporation
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Creating an NI-DAQmx Task
In NI-DAQmx, a task is a collection of one or more channels, timing,
triggering, and other properties. Conceptually, a task represents a
measurement or generation you want to perform. For example, you can
create a task to measure temperature from one or more channels on a DAQ
device.
Complete the following steps to create and configure a task that reads a
voltage level from a DAQ device.
1.
Open a new VI.
2.
On the block diagram, select the Input palette on the Functions
palette.
If the Functions palette is not visible, select View»Functions Palette.
3.
Select the DAQ Assistant Express VI, shown at left, on the Input
palette and place it on the block diagram. The DAQ Assistant launches
and the Create New dialog box appears.
4.
Click Analog Input to display the Analog Input options.
5.
Select Voltage to create a new voltage analog input task.
The dialog box displays a list of channels on each installed DAQ
device. The number of channels listed depends on the number of
channels you have on the DAQ device.
6.
Getting Started with LabVIEW
In the Supported Physical Channels list, select the physical channel
to which the instrument connects the signal, such as ai0, and then click
the Finish button. The DAQ Assistant opens a new dialog box, shown
in Figure 4-1, which displays options for configuring the channel you
selected to complete a task.
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Figure 4-1. Configuring a Task Using the DAQ Assistant
7.
In the Input Range section of the Settings page, enter 10 for the Max
value and enter -10 for the Min value.
8.
On the Task Timing page, select the N Samples option.
9.
Enter a value of 1000 in the Samples To Read text box.
© National Instruments Corporation
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Testing the Task
You can test the task to verify that you correctly configured the channel.
Complete the following steps to confirm that you are acquiring data.
1.
Click the Test button, shown at left. The DAQ Assistant dialog box
appears.
2.
Click the Start button once or twice to confirm that you are acquiring
data, and then click the Close button to return to the DAQ Assistant.
3.
Click the OK button to save the current configuration and close
the DAQ Assistant.
4.
Save the VI as Read Voltage.vi in an easily accessible location.
Graphing Data from a DAQ Device
You can use the task you created in the previous exercise to graph the data
acquired from a DAQ device.
Complete the following steps to plot the data from the channel on a
waveform graph and change the name of the signal.
1.
On the block diagram, right-click the data output and select Create»
Graph Indicator from the shortcut menu.
2.
Display the front panel and run the VI three or four times. Observe the
waveform graph.
Voltage appears in the waveform graph plot legend.
3.
On the block diagram, right-click the DAQ Assistant Express VI and
select Properties from the shortcut menu to open the DAQ Assistant.
4.
Right-click Voltage in the list of channels and select Rename from the
shortcut menu to display the Rename a channel or channels dialog
box.
You also can select the name of the channel and press the <F2> key to display the
Rename a channel or channels dialog box.
Tip
5.
In the New Name text box, enter First Voltage Reading, and
click the OK button.
6.
Click the OK button to save the current configuration and close
the DAQ Assistant.
7.
Display the front panel and run the VI.
First Voltage Reading appears in the waveform graph plot legend.
8.
Getting Started with LabVIEW
Save the VI.
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Editing an NI-DAQmx Task
You can add a channel to the task so you can compare two separate voltage
readings. You also can customize the task to acquire the voltage readings
continuously.
Complete the following steps to add a new channel to the task and acquire
data continuously.
1.
On the block diagram, double-click the DAQ Assistant Express VI to
open the DAQ Assistant.
2.
Click the Add Channels button, shown at left, and select the Voltage
channel from the Add Channel menu to display the Add Channels To
Task dialog box.
3.
Select any unused physical channel in the Supported Physical
Channels list, and click the OK button to return to the DAQ Assistant.
4.
Rename the channel Second Voltage Reading.
5.
On the Task Timing page, select the Continuous option.
When you set timing and triggering options in the DAQ Assistant,
these options apply to all the channels in the list of channels.
6.
Click the OK button to save the current configuration and close
the DAQ Assistant. The Confirm Auto Loop Creation dialog box
appears.
7.
Click the Yes button. LabVIEW places a While Loop around the DAQ
Assistant Express VI and the graph indicator. A stop button appears on
the block diagram wired to the stop input of the DAQ Assistant
Express VI. The stopped output of the Express VI is wired to the
conditional terminal of the While Loop. The block diagram should
appear similar to Figure 4-2.
Figure 4-2. Block Diagram of the Read Voltage VI
© National Instruments Corporation
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If an error occurs or you click the stop button while the VI is running,
the DAQ Assistant Express VI stops reading data and the stopped
output returns a TRUE value and stops the While Loop.
Visually Comparing Two Voltage Readings
Because you have two voltage readings displayed on a graph, you can
customize the plots to distinguish between the two.
Complete the following steps to customize the plot color on the waveform
graph.
1.
On the front panel, expand the plot legend to display two plots.
2.
Run the VI.
Two plots appear on the graph, and the plot legend displays both plot
names.
3.
Right-click First Voltage Reading in the plot legend and select Color
from the shortcut menu. Using the color picker, select a color such as
yellow so the plot is easy to read. Change the plot color of Second
Voltage Reading.
4.
Save the VI.
Communicating with an Instrument
Instrument drivers simplify instrument control and reduce test program
development time by eliminating the need to learn the programming
protocol for each instrument. An instrument driver is a set of software
routines that control a programmable instrument. Each routine corresponds
to a programmatic operation such as configuring, reading from, writing to,
and triggering the instrument. Use an instrument driver for instrument
control when possible. National Instruments provides thousands of
instrument drivers for a wide variety of instruments.
Use the NI Instrument Driver Finder to search for and install instrument
drivers without leaving the LabVIEW development environment. Select
Help»Find Instrument Drivers to launch the Instrument Driver Finder.
You also can visit the NI Instrument Driver Network at ni.com/idnet to
find a driver for an instrument.
If a driver is not available for an instrument, you can use the Instrument I/O
Assistant Express VI to communicate with the instrument.
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Note You must have the Instrument I/O Assistant and an instrument installed to use the
Instrument I/O Assistant Express VI. You install the Instrument I/O Assistant from the
National Instruments Device Drivers CD.
In the following exercises, you will communicate with an instrument.
Selecting an Instrument
Before you communicate with an instrument, you must select the
instrument with which you want to communicate.
Complete the following steps to use the Instrument I/O Assistant Express
VI to select an instrument.
1.
Turn on the instrument you want to use. The instrument must be
powered on to use the Instrument I/O Assistant Express VI.
2.
Select the Instrument I/O Assistant Express VI on the Input palette
and place it on the block diagram. The Instrument I/O Assistant
dialog box appears.
3.
Click the Show Help button, shown at left, in the upper right corner of
the Instrument I/O Assistant dialog box.
The help appears to the right of the dialog box. The top help window
contains how-to information about using the Instrument I/O Assistant.
The bottom help window provides context-sensitive help about
components in the dialog box.
4.
Click the Select Instrument link in the top help window and follow
the instructions in the help window to select the instrument with which
you want to communicate.
5.
If necessary, configure the properties of the instrument.
6.
If you want to minimize the help window, click the Hide Help button,
shown at left, in the upper right corner of the Instrument I/O
Assistant dialog box.
Acquiring and Parsing Information for an Instrument
After you select the instrument, you can send commands to the instrument
to retrieve data. In this exercise, you will learn to use the Instrument I/O
Assistant Express VI to acquire and parse identification information for an
instrument.
Complete the following steps to communicate with the instrument.
1.
© National Instruments Corporation
In the Instrument I/O Assistant dialog box, click the Add Step
button and click the Query and Parse step.
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2.
Enter *IDN? in the Enter a command text box.
*IDN? is a query that most instruments recognize. The response is an
identification number string that describes the instrument. If the
instrument does not accept this command, refer to the reference
manual for the instrument for a list of commands the instrument does
accept.
3.
Click the Run button, shown at left.
The Instrument I/O Assistant sends the command to the instrument,
and the instrument returns its identification information.
4.
Select ASCII only from the pull-down menu below the Byte index
column of the response window to parse the instrument name as an
ASCII string. You also can use the Instrument I/O Assistant to parse
ASCII numbers and binary data.
5.
Click the Parsing help button, shown at left, in the Instrument I/O
Assistant dialog box to display information about parsing data.
6.
In the ASCII representation column of the response window, click
the value you want to parse.
7.
Enter a name for the token, or parsed data selection, in the Token
name text box.
8.
Click the OK button to save the current configuration and close the
Instrument I/O Assistant dialog box.
The name that you entered in the Token name text box is the output
of the Instrument I/O Assistant Express VI, shown at left.
Summary
The following topics are a summary of the main concepts you learned in
this chapter.
DAQ Assistant Express VI
You can use the DAQ Assistant Express VI to interactively build
measurement channels or tasks.
Place the DAQ Assistant Express VI on the block diagram to configure
channels and tasks for use with NI-DAQmx for data acquisition.
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NI-DAQmx is a programming interface you can use to communicate with
data acquisition devices. You can use the DAQ Assistant Express VI to
control devices supported by NI-DAQmx.
Refer to the Getting Started»Taking an NI-DAQmx Measurement in
LabVIEW book on the Contents tab in the LabVIEW Help for information
about the DAQ Assistant.
Refer to the National Instruments Web site at ni.com/daq for information
about devices supported by NI-DAQmx. If NI-DAQmx does not support
the device you want to use, refer to the Taking Measurements book on the
Contents tab in the LabVIEW Help for information about using Traditional
NI-DAQ (Legacy) for data acquisition.
Tasks
In NI-DAQmx, a task is a collection of one or more channels, timing,
triggering, and other properties. Conceptually, a task represents a
measurement or generation you want to perform.
For example, you can configure a collection of channels for analog input
operations. After you create a task, you can access the single task instead
of configuring the channels individually to perform analog input
operations. After you create a task, you can add or remove channels from
that task.
Refer to the Taking Measurements book on the Contents tab in the
LabVIEW Help for more information about channels and tasks.
Instrument I/O Assistant Express VI
An instrument driver is a set of software routines that control a
programmable instrument. Each routine corresponds to a programmatic
operation such as configuring, reading from, writing to, and triggering the
instrument. Use an instrument driver for instrument control when possible.
National Instruments provides thousands of instrument drivers for a wide
variety of instruments.
Use the NI Instrument Driver Finder to search for and install instrument
drivers without leaving the LabVIEW development environment. Select
Help»Find Instrument Drivers to launch the Instrument Driver Finder.
You also can visit the NI Instrument Driver Network at ni.com/idnet to
find a driver for an instrument.
© National Instruments Corporation
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If a driver is not available for an instrument, you can use the Instrument I/O
Assistant Express VI to communicate with the instrument. You can use the
Instrument I/O Assistant to communicate with message-based instruments
and graphically parse the response. Start the Instrument I/O Assistant by
placing the Instrument I/O Assistant Express VI on the block diagram or by
double-clicking the Instrument I/O Assistant Express VI icon on the block
diagram.
Refer to the Instrument I/O Assistant Help for information about
communicating with an external device. Display the Instrument I/O
Assistant Help by clicking the Show Help button in the Instrument I/O
Assistant dialog box.
Getting Started with LabVIEW
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Using Other LabVIEW Features
5
The previous chapters in this manual introduce you to most of the
LabVIEW features you need to build common measurement applications.
As you familiarize yourself with the LabVIEW environment, you might
find that you need to enhance VIs or that you need more fine-tuned control
of the processes the VIs perform. This chapter introduces you to some of
the concepts you should be familiar with as you start using other LabVIEW
features. Refer to the Fundamentals book on the Contents tab in the
LabVIEW Help for more information about these concepts. The Concepts
books contain information about LabVIEW programming concepts, and
the How-To books contain step-by-step instructions for using LabVIEW.
All Controls and Indicators
The controls and indicators located on the Express subpalette of the
Controls palette are a subset of the complete set of built-in controls and
indicators available in LabVIEW. You can find all the controls and
indicators that you can use to create the front panel on other subpalettes.
However, subpalettes other than the Express subpalette categorize controls
and indicators by functionality instead of having a subpalette for controls
and a subpalette for indicators.
For example, the top level of the Express subpalette has a Numeric
Controls subpalette and a Numeric Indicators subpalette. On the Modern
and Classic subpalettes, these controls and indicators are located on the
Numeric subpalette because they are all numeric objects.
Click the View button on the pinned Controls palette and select Always
Visible Categories»Show All Categories from the shortcut menu to
display all categories on the Controls palette.
Refer to the Fundamentals»Building the Front Panel book on the
Contents tab in the LabVIEW Help for more information about using the
complete set of built-in controls and indicators available in LabVIEW.
© National Instruments Corporation
5-1
Getting Started with LabVIEW
Chapter 5
Using Other LabVIEW Features
All VIs and Functions
The Express VIs and structures located on the Express subpalette of the
Functions palette are a subset of the complete set of built-in VIs, functions,
and structures available in LabVIEW.
Click the View button on the pinned Functions palette and select Always
Visible Categories»Show All Categories from the shortcut menu to
display all categories on the Functions palette.
LabVIEW uses colored icons to distinguish between functions, VIs, and
Express VIs. Icons for functions have pale yellow backgrounds, most icons
for VIs have white backgrounds, and icons for Express VIs appear
surrounded by pale blue fields.
Express VIs appear on the block diagram as expandable nodes with icons
surrounded by a blue field. Unlike Express VIs, most functions and VIs on
the block diagram appear as icons rather than expandable nodes.
VIs
When you place a VI on the block diagram, the VI is a subVI. When you
double-click a subVI, its front panel appears, rather than a dialog box in
which you can configure options.
The icon for a VI appears in the upper right corner of the front panel and
block diagram. This icon is the same as the icon that appears when you
place the VI on the block diagram.
You can use a VI you create as a subVI. Refer to the Fundamentals»
Creating VIs and SubVIs book on the Contents tab in the LabVIEW Help
for more information about creating VIs and configuring them as subVIs.
You also can save the configuration of an Express VI as a subVI. Refer to
the Fundamentals»Building the Block Diagram book on the Contents
tab in the LabVIEW Help for more information about creating subVIs from
Express VIs.
Functions
Functions are the fundamental operating elements of LabVIEW. Unlike
VIs, functions do not have front panels or block diagrams.
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Chapter 5
Using Other LabVIEW Features
Data Types
On the block diagram of a VI, the terminals for the front panel objects are
different colors. The color and symbol of a terminal indicate the data type
of the corresponding control or indicator. Colors also indicate the data types
of wires, inputs, and outputs. The color of inputs and outputs of Express
VIs indicate what type of data the input or output accepts or returns.
Data types indicate which objects, inputs, and outputs you can wire
together. For example, a switch has a green border, so you can wire a switch
to any Express VI input with a green label. A knob has an orange border,
so you can wire a knob to any Express VI input with an orange label.
However, you cannot wire a knob to an input with a green label. The wires
you create are the same color as the terminal.
Refer to the Fundamentals»Building the Block Diagram book on the
Contents tab in the LabVIEW Help for more information about data types.
Dynamic Data Type
Dynamic data stores the information generated or acquired by an Express
VI. The dynamic data type appears as a dark blue terminal, shown at left.
Most Express VIs accept or return dynamic data. You can wire dynamic
data to any indicator or input that accepts numeric, waveform, or Boolean
data. Wire dynamic data to an indicator that can best present the data. Such
indicators include graphs, charts, and numeric indicators.
Most other VIs and functions in LabVIEW do not accept dynamic data. To
use a built-in VI or function to analyze or process dynamic data, you must
convert the dynamic data to numeric, Boolean, waveform, or array data.
Use the Convert from Dynamic Data Express VI to convert dynamic data
to numeric, Boolean, waveform, and array data for use with other VIs and
functions. When you wire dynamic data to an array indicator, LabVIEW
inserts the Convert from Dynamic Data Express VI on the block diagram.
Use the Convert to Dynamic Data Express VI to convert numeric, Boolean,
waveform, and array data to dynamic data for use with Express VIs.
Refer to the Fundamentals»Building the Block Diagram book on the
Contents tab in the LabVIEW Help for more information about dynamic
data types.
© National Instruments Corporation
5-3
Getting Started with LabVIEW
Chapter 5
Using Other LabVIEW Features
When to Use Other LabVIEW Features
The Express VIs, structures, and controls and indicators located on the
Express subpalettes of the Controls and Functions palettes provide the
functionality you need to build common measurement applications. The
following list describes the applications that require you to use the VIs,
functions, structures, controls, and indicators located on subpalettes other
than the Express subpalette.
Getting Started with LabVIEW
•
Programatically control properties and methods for the
LabVIEW environment, VIs, and controls and indicators—You
can control programatically how a VI behaves when it runs, set the
appearance of a control or indicator, or control how the LabVIEW
environment behaves. Refer to the Fundamentals»Programatically
Controlling VIs book on the Contents tab in the LabVIEW Help for
more information about these features.
•
Call code written in text-based languages—You can use LabVIEW
to communicate with applications written in a text-based programming
language, such as C or C++. Refer to the Fundamentals»Calling
Code Written in Text-Based Programming Languages book on the
Contents tab in the LabVIEW Help for more information about these
features.
•
Communicate with VIs across a network—You can call a VI that
resides on another computer running LabVIEW. Refer to the
Fundamentals»Networking in LabVIEW book on the Contents tab
in the LabVIEW Help for more information about these features.
•
Publish VIs on the Web—You can publish the front panel of any VI
on the Web, where users can interact with the front panel. Refer to the
Fundamentals»Networking in LabVIEW book on the Contents tab
in the LabVIEW Help for more information about these features.
•
Save data to a variety of file formats—In addition to the text-based
measurement file format, you can create files that other applications
can use, such as text files and spreadsheet files. Refer to the
Fundamentals»File I/O book on the Contents tab in the LabVIEW
Help for more information about these features.
•
Customize menus—You can configure which menu items appear
when a user runs a VI. You also can create custom menus. Refer to the
Fundamentals»Creating VIs and SubVIs book on the Contents tab
in the LabVIEW Help for more information about these features.
•
Use LabVIEW projects—You can use projects to group together
LabVIEW files and non-LabVIEW files, create build specifications,
and deploy or download files to multiple targets from one location. You
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Chapter 5
Using Other LabVIEW Features
must use a project to build applications and shared libraries. You also
must use a project to work with an RT, FPGA, or PDA target. Refer to
the specific module documentation for more information about using
projects with the RT, FPGA, and PDA Modules. Refer to the
Fundamentals»Organizing and Managing a Project book on the
Contents tab in the LabVIEW Help for more information about using
LabVIEW projects.
© National Instruments Corporation
5-5
Getting Started with LabVIEW
Technical Support and
Professional Services
A
Visit the following sections of the National Instruments Web site at
ni.com for technical support and professional services:
•
Support—Online technical support resources at ni.com/support
include the following:
–
Self-Help Resources—For answers and solutions, visit the
award-winning National Instruments Web site for software drivers
and updates, a searchable KnowledgeBase, product manuals,
step-by-step troubleshooting wizards, thousands of example
programs, tutorials, application notes, instrument drivers, and
so on.
–
Free Technical Support—All registered users receive free Basic
Service, which includes access to hundreds of Application
Engineers worldwide in the NI Developer Exchange at
ni.com/exchange. National Instruments Application Engineers
make sure every question receives an answer.
For information about other technical support options in your
area, visit ni.com/services or contact your local office at
ni.com/contact.
•
Training and Certification—Visit ni.com/training for
self-paced training, eLearning virtual classrooms, interactive CDs,
and Certification program information. You also can register for
instructor-led, hands-on courses at locations around the world.
•
System Integration—If you have time constraints, limited in-house
technical resources, or other project challenges, National Instruments
Alliance Partner members can help. To learn more, call your local
NI office or visit ni.com/alliance.
If you searched ni.com and could not find the answers you need, contact
your local office or NI corporate headquarters. Phone numbers for our
worldwide offices are listed at the front of this manual. You also can visit
the Worldwide Offices section of ni.com/niglobal to access the branch
office Web sites, which provide up-to-date contact information, support
phone numbers, email addresses, and current events.
© National Instruments Corporation
A-1
Getting Started with LabVIEW
Glossary
A
automatic scaling
Ability of scales to adjust to the range of plotted values. On graph scales,
autoscaling determines maximum and minimum scale values.
B
block diagram
Pictorial description or representation of a program or algorithm. The block
diagram consists of executable icons called nodes and wires that carry data
between the nodes. The block diagram is the source code for the VI. The
block diagram resides in the block diagram window of the VI.
Boolean controls
and indicators
Front panel objects to manipulate and display Boolean (TRUE or FALSE)
data.
broken Run button
Button that replaces the Run button when a VI cannot run because of
errors.
broken VI
VI that cannot run because of errors; signified by a broken arrow in the
broken Run button.
© National Instruments Corporation
G-1
Getting Started with LabVIEW
Glossary
C
channel
1. Physical—a terminal or pin at which you can measure or generate an
analog or digital signal. A single physical channel can include more than
one terminal, as in the case of a differential analog input channel or a digital
port of eight lines. The name used for a counter physical channel is an
exception because that physical channel name is not the name of the
terminal where the counter measures or generates the digital signal.
2. Virtual—a collection of property settings that can include a name, a
physical channel, input terminal connections, the type of measurement or
generation, and scaling information. You can define NI-DAQmx virtual
channels outside a task (global) or inside a task (local). Configuring virtual
channels is optional in Traditional NI-DAQ and earlier versions but is
integral to every measurement you take in NI-DAQmx. In Traditional
NI-DAQ, you configure virtual channels in MAX. In NI-DAQmx, you can
configure virtual channels either in MAX or in a program, and you can
configure channels as part of a task or separately.
3. Switch—a switch channel represents any connection point on a switch.
It can be made up of one or more signal wires (commonly one, two, or
four), depending on the switch topology. A virtual channel cannot be
created with a switch channel. Switch channels may be used only in the
NI-DAQmx Switch functions and VIs.
checkbox
Small square box in a dialog box which you can select or clear. Checkboxes
generally are associated with multiple options that you can set. You can
select more than one checkbox.
conditional terminal
Terminal of a While Loop that contains a Boolean value that determines if
the VI performs another iteration.
Context Help window
Window that displays basic information about LabVIEW objects when you
move the cursor over each object. Objects with context help information
include VIs, functions, constants, structures, palettes, properties, methods,
events, and dialog box components.
control
Front panel object for entering data to a VI interactively or to a subVI
programmatically, such as a knob, push button, or dial.
Controls palette
Palette that contains front panel controls, indicators, and decorative objects.
current VI
VI whose front panel, block diagram, or Icon Editor is the active window.
Getting Started with LabVIEW
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Glossary
D
DAQ
See data acquisition (DAQ).
DAQ Assistant
A graphical interface for configuring measurement tasks, channels, and
scales.
DAQ device
A device that acquires or generates data and can contain multiple channels
and conversion devices. DAQ devices include plug-in devices, PCMCIA
cards, and DAQPad devices, which connect to a computer USB or 1394
(FireWire) port. SCXI modules are considered DAQ devices.
data acquisition (DAQ)
1. Acquiring and measuring analog or digital electrical signals from
sensors, acquisition transducers, and test probes or fixtures.
2. Generating analog or digital electrical signals.
data flow
Programming system that consists of executable nodes that execute only
when they receive all required input data. The nodes produce output data
automatically when they execute. LabVIEW is a dataflow system. The
movement of data through the nodes determines the execution order of the
VIs and functions on the block diagram.
data type
Format for information. In LabVIEW, acceptable data types for most VIs
and functions are numeric, array, string, Boolean, path, refnum,
enumeration, waveform, and cluster.
default
Preset value. Many VI inputs use a default value if you do not specify a
value.
device
An instrument or controller you can access as a single entity that controls
or monitors real-world I/O points. A device often is connected to a host
computer through some type of communication network. See also DAQ
device and measurement device.
drag
To use the cursor on the screen to select, move, copy, or delete objects.
driver
Software that controls a specific hardware device, such as a DAQ device.
© National Instruments Corporation
G-3
Getting Started with LabVIEW
Glossary
E
error message
Indication of a software or hardware malfunction or of an unacceptable data
entry attempt.
Express VI
A subVI designed to aid in common measurement tasks. You configure an
Express VI using a configuration dialog box.
F
For Loop
Iterative loop structure that executes its subdiagram a set number of times.
Equivalent to text-based code: For i = 0 to n – 1, do....
front panel
Interactive user interface of a VI. Front panel appearance imitates physical
instruments, such as oscilloscopes and multimeters.
function
Built-in execution element, comparable to an operator, function, or
statement in a text-based programming language.
Functions palette
Palette that contains VIs, functions, block diagram structures, and
constants.
G
General Purpose
Interface Bus
GPIB. Synonymous with HP-IB. The standard bus used for controlling
electronic instruments with a computer. Also called IEEE 488 bus because
it is defined by ANSI/IEEE Standards 488-1978, 488.1-1987, and
488.2-1992.
graph
2D display of one or more plots. A graph receives and plots data as a block.
I
I/O
Input/Output. The transfer of data to or from a computer system involving
communications channels, operator input devices, and/or data acquisition
and control interfaces.
icon
Graphical representation of a node on a block diagram.
indicator
Front panel object that displays output, such as a graph or LED.
Getting Started with LabVIEW
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Glossary
instrument driver
A set of high-level functions that control and communicate with instrument
hardware in a system.
L
label
Text object used to name or describe objects or regions on the front panel
or block diagram.
LabVIEW
Laboratory Virtual Instrument Engineering Workbench. LabVIEW is a
graphical programming language that uses icons instead of lines of text to
create programs.
LED
Light-emitting diode.
legend
Object a graph or chart owns to display the names and plot styles of plots
on that graph or chart.
M
MAX
See Measurement & Automation Explorer.
Measurement &
Automation Explorer
The standard National Instruments hardware configuration and diagnostic
environment for Windows.
measurement device
DAQ devices such as the E Series multifunction I/O (MIO) devices, SCXI
signal conditioning modules, and switch modules.
menu bar
Horizontal bar that lists the names of the main menus of an application.
The menu bar appears below the title bar of a window. Each application has
a menu bar that is distinct for that application, although some menus
and commands are common to many applications.
N
NI-DAQ
Driver software included with all NI DAQ devices and signal conditioning
components. NI-DAQ is an extensive library of VIs and ANSI C functions
you can call from an application development environment (ADE), such as
LabVIEW, to program an NI measurement device, such as the M Series
multifunction I/O (MIO) DAQ devices, signal conditioning modules, and
switch modules.
© National Instruments Corporation
G-5
Getting Started with LabVIEW
Glossary
NI-DAQmx
The latest NI-DAQ driver with new VIs, functions, and development tools
for controlling measurement devices. The advantages of NI-DAQmx over
earlier versions of NI-DAQ include the DAQ Assistant for configuring
channels and measurement tasks for your device for use in LabVIEW,
LabWindows™/CVI™, and Measurement Studio; NI-DAQmx simulation
for most supported devices for testing and modifying applications without
plugging in hardware; and a simpler, more intuitive API for creating DAQ
applications using fewer functions and VIs than earlier versions of
NI-DAQ.
node
Program execution element. Nodes are analogous to statements, operators,
functions, and subroutines in text-based programming languages.
On a block diagram, nodes include functions, structures, and subVIs.
numeric controls
and indicators
Front panel objects to manipulate and display numeric data.
O
object
Generic term for any item on the front panel or block diagram, including
controls, indicators, structures, nodes, wires, and imported pictures.
Operating tool
Tool to enter data into controls or to operate them.
P
palette
Displays objects or tools you can use to build the front panel or block
diagram.
plot
Graphical representation of an array of data shown either on a graph or
a chart.
Positioning tool
Tool to move and resize objects.
pull-down menus
Menus accessed from a menu bar. Pull-down menu items are usually
general in nature.
PXI
PCI eXtensions for Instrumentation. A modular, computer-based
instrumentation platform.
Getting Started with LabVIEW
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Glossary
R
RMS
Root Mean Square.
S
sample
Single analog or digital input or output data point.
scale
Part of graph, chart, and some numeric controls and indicators that contains
a series of marks or points at known intervals to denote units of measure.
shortcut menu
Menu accessed by right-clicking an object. Menu items pertain to that
object specifically.
string
Representation of a value as text.
structure
Program control element, such as a Flat Sequence structure, Stacked
Sequence structure, Case structure, For Loop, or While Loop.
subVI
VI used on the block diagram of another VI. Comparable to a subroutine.
T
task
A collection of one or more channels, timing, triggering, and other
properties in NI-DAQmx. A task represents a measurement or generation
you want to perform.
terminal
Object or region on a node through which data pass.
tip strip
Small yellow text banners that identify the terminal name and make it easier
to identify terminals for wiring.
tool
Special cursor to perform specific operations.
toolbar
Bar that contains command buttons to run and debug VIs.
Traditional NI-DAQ
(Legacy)
An older driver with outdated APIs for developing data acquisition,
instrumentation, and control applications for older National Instruments
DAQ devices. You should use Traditional NI-DAQ (Legacy) only in certain
circumstances. Refer to the NI-DAQ Readme for more information about
when to use Traditional NI-DAQ (Legacy), including a complete list of
supported devices, operating systems, and application software and
language versions.
© National Instruments Corporation
G-7
Getting Started with LabVIEW
Glossary
V
VI
See virtual instrument (VI).
virtual instrument (VI)
Program in LabVIEW that models the appearance and function of a
physical instrument.
VXI
VME eXtensions for Instrumentation (bus).
W
waveform
Multiple voltage readings taken at a specific sampling rate.
waveform chart
Indicator that plots data points at a certain rate.
While Loop
Loop structure that repeats a section of code until a condition occurs.
wire
Data path between nodes.
Wiring tool
Tool to define data paths between terminals.
Getting Started with LabVIEW
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Index
Symbols
building
applications, 5-4
shared libraries, 5-4
button
adding, 2-10
placing on block diagram, 3-10
Run, 1-5
.lvm files, 2-9, 2-10, 2-13
.tdm files, 2-9, 2-10, 2-13
A
acquiring
information for instruments, 4-7
signals, 4-1
Acquiring a Signal VI block diagram
(figure), 1-12
adding
channels to tasks, 4-5
controls from the block diagram, 3-4
controls to the front panel, 1-5
graph indicators, 3-4
inputs to Express VIs, 1-8, 3-4
numeric indicators, 3-4
visual cues on front panel, 2-6
warning lights, 2-6
Amplitude and Level Measurements Express
VI, 2-2
analyzing voltage, 2-5
analyzing signals, 2-5
applications, building, 5-4
Arithmetic & Comparison palette, 1-10
C
calling code from text-based languages, 5-4
changing signal types, 1-6
channels, 4-2
adding to tasks, 4-5
renaming, 4-4
communicating
with instruments, 4-6, 4-10
with LabVIEW applications across
networks, 5-4
Comparison Express VI, setting warning
level, 2-7
configuration dialog boxes, 1-17
Context Help window, 2-2, 2-13, 3-2, 3-9
button, 3-2
displaying configuration of Express VIs, 2-2
displaying errors, 2-14
figure, 2-2
controlling execution speed, 3-6, 3-7, 3-11
controls, 1-16, 2-13, 5-1
adding from the block diagram, 3-4
adding to the front panel, 1-5
configuring, 1-17
creating, 3-4, 3-10
customizing, 1-13
data types, 5-3
numeric, 1-6, 5-1
palette, 1-5
B
block diagram, 1-5, 1-17
indicators, 2-13
modifying, 2-3
showing, 1-6
broken
Run button, 2-4
wires, 2-4, 2-14
Build Table Express VI, 3-8
© National Instruments Corporation
I-1
Getting Started with LabVIEW
Index
Controls palette, 1-5
figure, 1-6
showing all categories, 5-1
conventions used in this manual, ix
Convert from/to Dynamic Data Express VIs,
5-3
creating
controls, 3-4, 3-10
graph indicators, 3-4
indicators, 3-10
NI-DAQmx tasks, 4-2
customizing
block diagrams, 3-10
controls, 1-13
front panels, 3-4
indicators, 1-15
menus, 5-4
simulated signals, 2-3
documentation
conventions used in this manual, ix
introduction to this manual, ix
NI resources, A-1
related documentation, x
drivers
instrument, 4-6, 4-9
NI resources, A-1
dynamic data, 5-3
converting from and to, 5-3
E
Error list window, 2-4, 2-14
errors, 2-14
displaying, 2-4
displaying in Context Help window, 2-14
list, 2-4, 2-14
window, 2-4, 2-14
example VIs
NI Example Finder, 3-7
NI resources, A-1
Execution Control palette, 3-5, 3-11
execution speed, controlling, 3-6, 3-7, 3-11
Express VIs, 1-17
Amplitude and Level Measurements, 2-2,
2-5
Build Table, 3-8
Comparison, 2-7
configuration dialog boxes, 1-17
Convert from/to Dynamic Data, 5-3
DAQ Assistant, 4-2, 4-8
dynamic data, 5-3
inputs, 1-17
Instrument I/O Assistant, 4-6, 4-9
outputs, 1-17
Scaling and Mapping, 1-10
Simulate Signals, 1-6
Time Delay, 3-7
Write To Measurement File, 2-9, 2-13
D
DAQ Assistant Express VI, 4-2, 4-8
DAQ devices, 4-2
data
saving
to a file, 2-10
when prompted by a user, 2-11
storing, 2-10
data flow, 1-9, 1-12, 1-17
data types, dynamic, 5-3
deleting wires, 1-10
deselecting objects, 1-8
diagnostic tools (NI resources), A-1
displaying
data from DAQ devices, 4-4
data in tables, 3-8, 3-11
signals in a graph, 1-12
Getting Started with LabVIEW
I-2
ni.com
Index
F
I
files
indicators, 1-17, 2-13, 5-1
adding numeric, 3-4
configuring, 1-17
creating, 3-10
customizing, 1-15
data type, 5-3
numeric, 5-1
removing, 2-4
Input palette, 3-2
Instrument Driver Network, 4-6, 4-9
instrument drivers, 4-6, 4-9
NI resources, A-1
Instrument I/O Assistant Express VI, 4-6, 4-9
instruments
acquiring information, 4-7
communicating, 4-6, 4-10
parsing information, 4-7
selecting, 4-7
grouping, 5-4
saving to other formats, 5-4
front panel, 1-5, 1-16
Acquiring a Signal VI (figure), 1-2
adding
controls, 1-5
visual cues, 2-6
controls, 1-16, 2-13
customizing, 3-4
indicators, 1-17
modifying, 2-4
showing, 1-9
Warning Light VI (figure), 2-1
functions, 5-2
Merge Signals, 1-12, 3-4
Functions palette
figure, 1-10
showing all categories, 5-2
K
G
Knob Control, customizing (figure), 1-14
KnowledgeBase, A-1
Getting Started window, 1-3, 2-2
figure, 1-3
graph indicators, creating, 3-4
graphing
data from DAQ devices, 4-4
two signals, 1-12
grouping files, 5-4
L
LabVIEW
help resources, using, 3-9
other features, using, 5-1
projects, 5-4
LabVIEW Help, 2-13, 3-9
searching for Express VIs, 3-3
LEDs, palette, 2-6
figure, 2-6
LVM. See .lvm files
H
help
button, 2-5
Context Help window, 2-2, 2-13, 3-2, 3-9
LabVIEW Help, 2-5, 2-13, 3-9
LabVIEW resources, 2-13, 3-9
searching, 3-3, 3-6, 3-10
technical support, A-1
© National Instruments Corporation
I-3
Getting Started with LabVIEW
Index
M
showing all categories, 5-1, 5-2
Text Indicators, 3-8
parsing information for instruments, 4-7
placing objects on the block diagram from the
help, 3-10
Positioning tool, 1-8
programatically controlling VIs, 5-4
programming examples (NI resources), A-1
projects, 5-4
property dialog boxes, 1-17
publishing VIs on the Web, 5-4
manual. See documentation
marquee, 3-8
menus, customizing, 5-4
Merge Signals function, 1-12, 3-4
figure, 1-13
modifying
block diagrams, 2-3
front panels, 2-4
signals, 1-10, 3-3
N
R
National Instruments support and
services, A-1
New dialog box, 1-3, 1-16, 2-1, 2-2
figure, 1-4
NI Example Finder, 3-7
NI Instrument Driver Network, 4-6, 4-9
NI support and services, A-1
NI-DAQmx
creating tasks, 4-2
tasks, 4-2, 4-9
testing tasks, 4-4
Numeric Controls palette, 1-6
related documentation, x
Run button, 1-5, 1-9
broken, 2-4, 2-14
running VIs, 1-9
continuously, 3-5
S
saving data
different file formats, 5-4
Save Data VI block diagram (figure), 2-12
to files, 2-9, 2-10, 2-13
when prompted by user, 2-11, 2-12
Scaling and Mapping Express VI, 1-10
defining slope, 1-11
searching
examples, 3-7
help, 3-3, 3-6, 3-10
palettes, 2-7, 2-10
selecting
instruments, 4-7
objects, 1-8
shared libraries, building, 5-4
O
objects, deselecting, 1-8
Operating tool, 1-9
P
palettes
Arithmetic & Comparison, 1-10
Controls, 1-5
Execution Control, 3-5, 3-11
Functions, 1-10
Input, 3-2
Numeric Controls, 1-6
searching, 2-7, 2-10
Getting Started with LabVIEW
I-4
ni.com
Index
V
signals
acquiring, 4-1
analyzing, 2-5
changing type, 1-6
modifying, 1-10, 3-3
Simulate Signal Express VI, 1-6
software (NI resources), A-1
virtual instruments. See VIs
VIs, 1-1, 5-2
blank, 3-1
building, 1-1, 2-1
customizing menus, 5-4
icons, 5-2
new, 3-1
programmatically controlling, 5-4
publishing on the Web, 5-4
running, 1-9
subVIs, 5-2
template, 1-2, 1-3, 1-16
T
tables, 3-8
displaying data, 3-11
tasks
adding new channels, 4-5
NI-DAQmx, 4-9
testing, 4-4
TDM. See .tdm files
technical support, A-1
template VIs, 1-2, 1-3, 1-16
Text Indicators palette, 3-8
text-based languages, calling code, 5-4
Time Delay Express VI, 3-7
tools
Operating, 1-9
Positioning, 1-8
Wiring, 1-8
training and certification (NI resources), A-1
troubleshooting (NI resources), A-1
W
Warning Light VI block diagram (figure), 2-8
Web resources, A-1
While Loop, 3-6
wires
broken, 2-4, 2-14
deleting, 1-10
wiring
objects on the block diagram, 1-8
tool, 1-8
Write to Measurement File Express VI, 2-9,
2-10, 2-13
saving data, 2-10
U
user interface. See front panel
© National Instruments Corporation
I-5
Getting Started with LabVIEW