CHAPTER 1

• 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 front panel, 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.

BUIDING A VIRTUAL INSTRUMENT

In the following exercises, you will build a VI that generates a signal and

displays that signal in a graph. After you complete the exercises, the front

panel of the VI will look similar to the front panel.

• Launching LabView

The Getting Started window 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.

The Getting Started window disappears when you open an existing file or

create a new file. The Getting Started window reappears when you close

all open front panels and block diagrams. You also can display the window

from the front panel or block diagram by selecting View»Getting Started

Window.

• Opening a New VI from a Template

LabVIEW provides built-in template VIs that include the subVIs,

functions, structures, and front panel objects you need to get started

building common measurement applications.

Complete the following steps to create a VI that generates a signal and

displays it in the front panel window.

1. Launch LabVIEW.

2. In the Getting Started window, click the New or VI from Template

link to display the New dialog box.

3. From the Create New list, select VI»From Template»Tutorial

(Getting Started)»Generate and Display. This template VI

generates and displays a signal.

A preview and a brief description of the template VI appear in the

Description section. 

4. Click the OK button to create a VI from the template. You also can

double-click the name of the template VI in the Create New list to

create a VI from a template.

LabVIEW displays two windows: the front panel window and the

block diagram window.

5. Examine the front panel window.

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.

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.

A sine wave appears on the graph in the front panel window.

8. Stop the VI by clicking the front panel STOP button, shown at left.

• Adding a Control to the Front Panel

Front panel controls 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.

1. If the Controls palette is not visible in the front

panel window, select View»Controls Palette.

2. If you are a new LabVIEW user, the Controls palette opens with the

Express palette visible by default. If you do not

see the Express palette, click Express on the Controls palette to

display the Express palette.

3. Move the cursor over the icons on the Express 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.

4. Click the Numeric Controls icon to display the Numeric Controls

palette.

5. Click the Knob control on the Numeric Controls palette to attach the

control to the cursor, and then add the knob to the front panel to the left

of the waveform graph.

You will use this knob in a later exercise to control the amplitude of a

signal.

6. Select File»Save As and save the VI as Acquiring a Signal.vi in

an easily accessible location.

• Changing a Signal Type

The block diagram has a blue icon labeled Simulate Signal. This icon

represents the Simulate Signal Express VI. 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 sine wave

by default.

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

1. Display the block diagram by pressing the <Ctrl-E> keys or by

clicking the block diagram.

Locate the Simulate Signal Express VI, shown at left. 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 X) Press <Command>-click to perform the same

action as right-click.

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. 

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

inputs and outputs 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.

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 to change the amplitude of the signal, you must connect

two objects on the block diagram.

Complete the following steps to wire the knob to the Amplitude input of

the Simulate Signal Express VI.

1. On the block diagram, move the cursor over the Knob terminal, shown

at left.

The cursor becomes an arrow, or the Positioning tool, shown at left.

Use the Positioning tool to select, position, and resize objects.

2. Use the Positioning tool to select the Knob terminal and make sure it

is to the left of the Simulate Signal Express VI and inside the gray loop,

shown at left.

The terminals inside the loop are representations of front panel

controls and indicators. Terminals are entry and exit ports that

exchange information between the front panel and block diagram.

3. Deselect the Knob terminal by clicking a blank space on the block

diagram. If you want to use a different tool with an object, you must

deselect the object to switch the tool.

4. Move the cursor over the arrow on the Knob terminal, shown at left.

The cursor becomes a wire spool, or the Wiring tool, shown at left. Use

the Wiring tool to wire objects together on the block diagram.

5. When the Wiring tool appears, click the arrow on the Knob terminal

and then click the arrow on the Amplitude input of the Simulate Signal

Express VI, shown at left, to wire the two objects together.

A wire appears and connects the two objects. Data flows along this

wire from the Knob terminal to the Express VI.

6. Select File»Save to save the VI.

• Running a VI

Running a VI executes the solution.

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

1. Display the front panel by pressing the <Ctrl-E> keys or by clicking

the front panel.

2. Click the Run button or press the <Ctrl-R> keys to run the VI.

3. Move the cursor over the knob.

The cursor becomes a hand, or the Operating tool, shown at left. Use

the Operating tool to change the value of a control.

4. Using the Operating tool, turn the knob to adjust the amplitude of the

sawtooth wave.

The amplitude of the sawtooth wave changes as you turn the knob. As

you change the amplitude, the Operating tool displays a tip strip that

indicates the numeric value of the knob. The y-axis on the graph scales

automatically to account for the change in amplitude.

To indicate that the VI is running, the Run button changes to a

darkened arrow, shown at left. You can change the value of most

controls while a VI runs, but you cannot edit the VI in other ways while

the VI runs.

5. Click the STOP button, shown at left, to stop the VI.

The STOP button stops the VI after the loop completes its current

iteration. The Abort Execution button, shown at left, stops the VI

immediately, before the VI finishes the current iteration. Aborting a VI

that uses external resources, such as external hardware, might leave the

resources in an unknown state by not resetting or releasing them

properly. Design the VIs you create with a stop button to avoid this

problem.

• Modifying a Signal

Complete the following steps to scale the signal by 10 and display the

results in the front panel graph.

1. In the block diagram, use the Positioning tool to 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 is not visible, select

View»Functions Palette to display it. The Functions palette opens

with the Express palette visible by default. If you have selected

another palette, you can return to the Express palette by clicking

Express on the Functions palette.

4. On the Arithmetic & Comparison palette, select the Formula Express

VI, shown at left, and place it on the block diagram 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.

The Configure Formula dialog box appears when you place the

Express VI on the block diagram. When you place an Express VI on

the block diagram, the configuration dialog box for that VI always

appears automatically.

5. Click the Help button, shown at left, in the bottom right corner of the

Configure Formula dialog box to display the LabVIEW Help topic for

this Express VI.

6. In the Formula topic, find the dialog box option whose description

indicates that it enters a variable into the formula.

7. Minimize the LabVIEW Help to return to the Configure Formula

dialog box.

8. Change the text in the Label column of the dialog box option you read

about, shown at left, from X1 to Sawtooth to indicate the input value

to the Formula Express VI. When you click in the Formula text box at

the top of the Configure Formula dialog box, the text changes to

match the label you entered.

9. Define the value of the scaling factor by entering *10 after Sawtooth

in the Formula text box.

You can use the Input buttons in the configuration dialog box or you

can use the *, 1, and 0 keyboard buttons to enter the scaling factor. If

you use the Input buttons in the configuration dialog box, LabVIEW

places the formula input after the Sawtooth input in the Formula text

box. If you use the keyboard, click in the Formula text box after

Sawtooth and enter the formula you want to appear in the text box.

10. Click the OK button to save the current configuration and close the

Configure Formula dialog box.

11. Move the cursor over the arrow on the Sawtooth output of the

Simulate Signal Express VI.

12. When the Wiring tool appears, click the arrow on the Sawtooth output

and then click the arrow on the Sawtooth input of the Formula Express

VI, shown at left, to wire the two objects together.

13. Use the Wiring tool to wire the Result output of the Formula Express

VI to the Waveform Graph terminal.

14. 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 Formula Express VI on the same graph, use the

Merge Signals function.

Complete the following steps to display two signals on the same graph.

1. In 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.

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 original sawtooth wave and the scaled sawtooth

wave with 10 times the amplitude, as you specified in the Formula

Express VI. The maximum value on the y-axis automatically scales as

you turn the knob.

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.

1. Right-click the front panel knob and select Properties from the

shortcut menu to display the Knob Properties dialog box. Click the

Appearance tab to display the Appearance page.

2. In the Label section on the Appearance page, delete the label Knob,

and enter Amplitude in the text box.

3. Click the Scale tab. In the Scale Style section, place a checkmark in

the Show color ramp checkbox.

The knob in the front panel window updates to reflect these changes.

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.

• 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. In the front panel window, 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, click and

drag the border of the plot legend to add one item to the legend. When

you release the mouse button, the second plot name appears.

3. Right-click the waveform graph and select Properties from the

shortcut menu to display the Graph Properties dialog box.

4. On the Plots page, select Sawtooth from the top 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 (Formula Result) from the top pull-down menu.

6. Place a checkmark in the Do not use waveform names for plot names

checkbox. This action lets you edit the labels on the graph.

7. In the Name text box, delete the current label and change the name of

this plot to Scaled Sawtooth.

8. Click the OK button to save the current configuration and close the

Graph Properties dialog box.

The plot color and plot legend change.

9. Reopen the 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.