Getting Started with LabVIEW: Editing NI-DAQmx Tasks and Using Other LabVIEW Features - Pr, Lab Reports of Mechanical Engineering

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LabVIEWTM Getting Started with LabVIEW Getting Started with LabVIEW August 2006 323427C-01 Support Worldwide Technical Support and Product Information ni.com National Instruments Corporate Headquarters 11500 North Mopac Expressway Austin, Texas 78759-3504 USA Tel: 512 683 0100 Worldwide Offices Australia 1800 300 800, Austria 43 0 662 45 79 90 0, Belgium 32 0 2 757 00 20, Brazil 55 11 3262 3599, Canada 800 433 3488, China 86 21 6555 7838, Czech Republic 420 224 235 774, Denmark 45 45 76 26 00, Finland 385 0 9 725 725 11, France 33 0 1 48 14 24 24, Germany 49 0 89 741 31 30, India 91 80 41190000, Israel 972 0 3 6393737, Italy 39 02 413091, Japan 81 3 5472 2970, Korea 82 02 3451 3400, Lebanon 961 0 1 33 28 28, Malaysia 1800 887710, Mexico 01 800 010 0793, Netherlands 31 0 348 433 466, New Zealand 0800 553 322, Norway 47 0 66 90 76 60, Poland 48 22 3390150, Portugal 351 210 311 210, Russia 7 095 783 68 51, Singapore 1800 226 5886, Slovenia 386 3 425 4200, South Africa 27 0 11 805 8197, Spain 34 91 640 0085, Sweden 46 0 8 587 895 00, Switzerland 41 56 200 51 51, Taiwan 886 02 2377 2222, Thailand 662 278 6777, United Kingdom 44 0 1635 523545 For further support information, refer to the Technical Support and Professional Services appendix. 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All rights reserved. © National Instruments Corporation v Getting Started with LabVIEW 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 ..................................................................................1-7 Wiring Objects on the Block Diagram ............................................................1-9 Running a VI ...................................................................................................1-10 Modifying a Signal ..........................................................................................1-11 Displaying Two Signals on a Graph................................................................1-14 Customizing a Knob Control...........................................................................1-15 Customizing a Waveform Graph.....................................................................1-17 Summary ........................................................................................................................1-18 New Dialog Box and Template VIs ................................................................1-18 Front Panel.......................................................................................................1-18 Block Diagram.................................................................................................1-19 Front Panel and Block Diagram Tools ............................................................1-19 Running and Stopping a VI .............................................................................1-19 Express VIs......................................................................................................1-19 LabVIEW Documentation Resources .............................................................1-20 Property Dialog Boxes ....................................................................................1-20 Shortcuts ..........................................................................................................1-20 Chapter 2 Customizing a VI Building a VI from a Blank VI ......................................................................................2-1 Opening a Blank VI.........................................................................................2-2 Adding an Express VI That Simulates a Signal ..............................................2-2 Searching the Help and Modifying a Signal....................................................2-3 Customizing a User Interface from the Block Diagram..................................2-4 Configuring a VI to Run Continuously until the User Stops It .......................2-6 Using the Error List Window ..........................................................................2-7 Controlling the Speed of Execution ................................................................2-8 Contents Getting Started with LabVIEW vi ni.com Using a Table to Display Data ........................................................................ 2-8 Searching for Examples .................................................................................. 2-10 Summary........................................................................................................................ 2-11 Using the LabVIEW Help Resources ............................................................. 2-11 Customizing the Block Diagram Code ........................................................... 2-12 Creating Controls and Indicators ...................................................... 2-12 Controlling When a VI Stops Running............................................. 2-12 Errors and Broken Wires .................................................................. 2-12 Displaying Data in a Table ............................................................... 2-13 Using the NI Example Finder ......................................................................... 2-13 Shortcuts.......................................................................................................... 2-13 Chapter 3 Full and Professional: Analyzing and Saving a Signal Building an Analysis VI ................................................................................................ 3-1 Modifying a VI Created from a Template ...................................................... 3-2 Adding a Signal............................................................................................... 3-3 Adding Two Signals........................................................................................ 3-5 Filtering a Signal ............................................................................................. 3-6 Modifying the Appearance of Graphs............................................................. 3-7 Analyzing the Amplitude of a Signal.............................................................. 3-8 Controlling the Speed of Execution ................................................................ 3-9 Adding a Warning Light ................................................................................. 3-9 Setting a Warning Level Limit........................................................................ 3-10 Warning the User ............................................................................................ 3-11 Configuring a VI to Save Data to a File.......................................................... 3-13 Saving Data to a File ....................................................................................... 3-13 Adding a Button That Stores Data When Clicked .......................................... 3-14 Saving Data When Prompted by a User.......................................................... 3-14 Viewing Saved Data........................................................................................ 3-16 Summary........................................................................................................................ 3-17 Controls and Indicators ................................................................................... 3-17 Filtering Data .................................................................................................. 3-17 Saving Data ..................................................................................................... 3-17 Chapter 4 Hardware: 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 Contents © National Instruments Corporation vii Getting Started with LabVIEW Visually Comparing Two Voltage Readings...................................................4-6 Communicating with an Instrument ..............................................................................4-6 Finding and Installing Instrument Drivers (Windows and Linux) ..................4-6 Selecting an Instrument Using the Instrument I/O Assistant ..........................4-7 Acquiring and Parsing Information for an Instrument ....................................4-8 Wiring a Command to an Instrument ..............................................................4-9 Summary ........................................................................................................................4-10 DAQ Assistant Express VI..............................................................................4-10 Tasks................................................................................................................4-10 Instrument Drivers...........................................................................................4-11 Instrument I/O Assistant Express VI...............................................................4-11 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 About This Manual Getting Started with LabVIEW x ni.com monospace bold Bold text in this font denotes the messages and responses that the computer automatically prints to the screen. This font also emphasizes lines of code that are different from the other examples. Platform Text in this font denotes a specific platform and indicates that the text following it applies only to that platform. right-click (Mac OS) Press <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: • LabVIEW Release Notes—Use these release notes to install and uninstall LabVIEW. The release notes also describe the system requirements for the LabVIEW software, including the LabVIEW Application Builder. • LabVIEW Help—Use the LabVIEW Help to access information about LabVIEW programming concepts, step-by-step instructions for using LabVIEW, and reference information about LabVIEW VIs, functions, palettes, menus, tools, properties, methods, events, dialog boxes, and so on. The LabVIEW Help also lists the LabVIEW documentation resources available from National Instruments. Access the LabVIEW Help by selecting Help»Search the LabVIEW Help. • LabVIEW Quick Reference Card—Use this card as a reference for information about help resources, keyboard shortcuts, data type terminals, and tools for editing, execution, and debugging. © National Instruments Corporation 1-1 Getting Started with LabVIEW 1 Getting Started with LabVIEW Virtual Instruments LabVIEW programs are called virtual instruments, or VIs, because their appearance and operation imitate physical instruments, such as oscilloscopes and multimeters. LabVIEW contains a comprehensive set of tools for acquiring, analyzing, displaying, and storing data, as well as tools to help you troubleshoot code you write. In LabVIEW, you build a user interface, or front panel, with controls and indicators. Controls are knobs, push buttons, dials, and other input mechanisms. Indicators are graphs, LEDs, and other output displays. After you build the user interface, you add code using VIs and structures to control the front panel objects. The block diagram contains this code. You can use LabVIEW to communicate with hardware such as data acquisition, vision, and motion control devices, as well as GPIB, PXI, VXI, RS232, and RS485 instruments. Building a Virtual Instrument In the following exercises, you will build a VI that generates a signal and displays that signal in a graph. After you complete the exercises, the front panel of the VI will look similar to the front panel in Figure 1-1. You can complete the exercises in this chapter in approximately 40 minutes. Chapter 1 Getting Started with LabVIEW Virtual Instruments Getting Started with LabVIEW 1-2 ni.com 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. Chapter 1 Getting Started with LabVIEW Virtual Instruments © National Instruments Corporation 1-5 Getting Started with LabVIEW 5. 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. You also can switch between the front panel window and block diagram window at any time by pressing the <Ctrl-E> keys. The <Ctrl> key in keyboard shortcuts corresponds to the (Mac OS) <Option> or <Command> key or (Linux) <Alt> key. 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 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. Tip Throughout these exercises, you can undo recent edits by selecting Edit»Undo or pressing the <Ctrl-Z> keys. 1. If the Controls palette, shown in Figure 1-4, is not visible on the front panel, select View»Controls Palette . Tip You can right-click any blank space on the front panel or the block diagram to display a temporary version of the Controls or Functions palettes. The Controls or Functions palette appears with a thumbtack icon in the upper left corner. Click the thumbtack to pin the palette so it is no longer temporary. Chapter 1 Getting Started with LabVIEW Virtual Instruments Getting Started with LabVIEW 1-6 ni.com 2. If you are a new LabVIEW user, the Controls palette opens with the Express subpalette visible by default. If you do not see the Express subpalette, click Express on the Controls palette to display the Express subpalette. Figure 1-4. Controls Palette 3. Move the cursor over the icons on the Express subpalette to locate the Numeric Controls palette. When you move the cursor over icons on the Controls palette, the name of the subpalette, control, or indicator appears in a tip strip below the icon. 4. Click the Numeric Controls icon to display the Numeric Controls palette. 5. Click the knob control on the Numeric Controls palette to attach the control to the cursor, then place the knob on the front panel to the left of the waveform graph. You will use this knob in a later exercise to control the amplitude of a signal. 6. Select File»Save As and save the VI as Acquiring a Signal.vi in an easily accessible location. Chapter 1 Getting Started with LabVIEW Virtual Instruments © National Instruments Corporation 1-7 Getting Started with LabVIEW Changing a Signal Type The block diagram has a blue icon labeled Simulate Signal. This icon represents the Simulate Signal Express VI. The Simulate Signal Express VI simulates a sine wave by default. Complete the following steps to change this signal to a sawtooth wave. 1. Display the block diagram by pressing the <Ctrl-E> keys or by clicking the block diagram. Locate the Simulate Signal Express VI, shown at left. An Express VI is a component of the block diagram that you can configure to perform common measurement tasks. The Simulate Signal Express VI simulates a signal based on the configuration that you specify. 2. Right-click the Simulate Signal Express VI and select Properties from the shortcut menu to display the Configure Simulate Signal dialog box. (Mac OS) Press <Command>-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. Chapter 1 Getting Started with LabVIEW Virtual Instruments Getting Started with LabVIEW 1-10 ni.com Running a VI Running a VI executes the solution. Complete the following steps to run the Acquiring a Signal VI. 1. Display the front panel by pressing the <Ctrl-E> keys or by clicking the front panel. 2. Click the Run button or press the <Ctrl-R> keys to run the VI. 3. Move the cursor over the knob. The cursor becomes a hand, or the Operating tool, shown at left. Use the Operating tool to change the value of a control. 4. Using the Operating tool, turn the knob to adjust the amplitude of the sawtooth wave. The amplitude of the sawtooth wave changes as you turn the knob. As you change the amplitude, the Operating tool displays a tip strip that indicates the numeric value of the knob. The y-axis on the graph scales automatically to account for the change in amplitude. To indicate that the VI is running, the Run button changes to a darkened arrow, shown at left. You can change the value of most controls while a VI runs, but you cannot edit the VI in other ways while the VI runs. 5. Click the STOP button, shown at left, to stop the VI. The STOP button stops the VI after the VI completes the current iteration. The Abort Execution button, shown at left, stops the VI immediately, before the VI finishes the current iteration. Aborting a VI that uses external resources, such as external hardware, might leave the resources in an unknown state by not resetting or releasing them properly. Design the VIs you create with a stop button to avoid this problem. Chapter 1 Getting Started with LabVIEW Virtual Instruments © National Instruments Corporation 1-11 Getting Started with LabVIEW Modifying a Signal Complete the following steps to scale the signal by 10 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 Formula 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. 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. The Formula help topic describes the Express VI, the configuration dialog box options, and the inputs and outputs of the Express VI. Each Express VI has a corresponding help topic you can access by clicking Chapter 1 Getting Started with LabVIEW Virtual Instruments Getting Started with LabVIEW 1-12 ni.com the Help button in the configuration dialog box or by right-clicking the Express VI and selecting Help from the shortcut menu. 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 text box of the dialog box option you read about from X1 to Sawtooth to indicate the input value to the Formula Express VI. When you click in the String 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 String 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 String text box. If you use the keyboard, click in the String text box after Sawtooth and enter the formula you want to appear in the text box. Chapter 1 Getting Started with LabVIEW Virtual Instruments © National Instruments Corporation 1-15 Getting Started with LabVIEW 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 configured the Formula Express VI to generate a slope of 10. 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. 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. Chapter 1 Getting Started with LabVIEW Virtual Instruments Getting Started with LabVIEW 1-16 ni.com 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. 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. Chapter 1 Getting Started with LabVIEW Virtual Instruments © National Instruments Corporation 1-17 Getting Started with LabVIEW 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 to add one item to the legend. When you release the mouse button, 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 (Formula Result) 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. Chapter 1 Getting Started with LabVIEW Virtual Instruments Getting Started with LabVIEW 1-20 ni.com 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. LabVIEW Documentation Resources 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, tools, properties, methods, events, dialog boxes, and so on. The LabVIEW Help also lists the LabVIEW documentation resources available from National Instruments. To access help information for Express VIs, click the Help button in the configuration dialog box while you configure an Express VI. 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. After you install a LabVIEW add-on such as a toolkit, module, or driver, the documentation for that add-on appears in the LabVIEW Help or appears in a separate help system you access by selecting Help»Add-On Help, where Add-On Help is the name of the separate help system for the add-on. 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. Shortcuts This chapter introduced the following keyboard shortcuts. Note The <Ctrl> key in these shortcuts corresponds to the (Mac OS) <Option> or <Command> key or (Linux) <Alt> key. Chapter 1 Getting Started with LabVIEW Virtual Instruments © National Instruments Corporation 1-21 Getting Started with LabVIEW Shortcut Function <Ctrl-R> Runs a VI. <Ctrl-Z> Undoes the last action. <Ctrl-E> Switches between the block diagram and the front panel window. <Ctrl-S> Saves a VI. Chapter 1 Getting Started with LabVIEW Virtual Instruments Getting Started with LabVIEW 1-22 ni.com Chapter 2 Customizing a VI © National Instruments Corporation 2-3 Getting Started with LabVIEW When you move the cursor over a VI, the Context Help window displays information about that VI. 3. Use the information that appears in the Context Help window to find the Express VI that can simulate a sine wave signal. Keep the Context Help window open. The context help provides useful information as you complete the rest of this exercise. 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), and Amplitude. 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. Click the OK button to save the current configuration and close the Configure Simulate Signal dialog box. 8. Move the cursor over the Simulate Signal Express VI and read the information that appears in the Context Help window. The Context Help window displays configuration information about 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. Chapter 2 Customizing a VI Getting Started with LabVIEW 2-4 ni.com 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 in the search results to display the topic that describes the Sample Compression Express VI. 4. After you read the description of the Express VI, click the 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. 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. A Mean indicator, shown at left, appears on the block diagram. 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. In a previous exercise you learned to add inputs and outputs by expanding the Express VI using the down arrows. Using the shortcut menu is a different way of displaying and selecting the inputs and outputs of an Express VI. Chapter 2 Customizing a VI © National Instruments Corporation 2-5 Getting Started with LabVIEW 3. Right-click the Enable input and select Create»Control from the shortcut menu to create a switch. A Boolean control, shown at left, appears on the block diagram. 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 2-3. Figure 2-3. 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. Note You might need to scroll or resize the front panel to see all controls and indicators. 8. Save the VI. Chapter 2 Customizing a VI Getting Started with LabVIEW 2-8 ni.com 8. Select View»Error List to display the Error list window. No errors appear in the errors and warnings field. Tip You also can press the <Ctrl-L> keys to display the Error list window. 9. Click the Close button to close the Error list window. The Run button no longer appears broken. 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. You can use the Time Delay Express VI to control the execution rate of the VI. 2. Enter 0.25 in the Time delay (seconds) text box. This time delay specifies how fast the loop runs. With a 0.25 second time delay, the loop iterates once every quarter of a second. 3. Click the OK button to save the current configuration and close the Configure Time Delay dialog box. 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. Chapter 2 Customizing a VI © National Instruments Corporation 2-9 Getting Started with LabVIEW 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 Sample Compression Express VI. If you drag objects near the border of the While Loop, the loop resizes to enclose the Build Table Express VI and the Table terminal. When you place an object in a While Loop near the border, the loop resizes to add space for that object. 5. Use the Wiring tool to wire the Mean output of the Sample Compression Express VI to the Signals input of the Build Table Express VI. The block diagram should appear similar to Figure 2-5. Figure 2-5. Block Diagram of the Reduce Samples VI 6. Display the front panel and run the VI. 7. Click the Enable switch. If the Enable switch is on, 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. Chapter 2 Customizing a VI Getting Started with LabVIEW 2-10 ni.com 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. 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. Tip 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. Refer to the Using Help book on the Contents tab in the LabVIEW Help for more information about searching help. 3. Click the Location column header to sort the search results by content type. Reference topics contain reference information about LabVIEW objects such as VIs, functions, palettes, menus, and tools. 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 search result to display the reference 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 examples similar to the example that uses this VI. The NI Example Finder searches among hundreds of examples, including all installed examples and the examples located on the NI Developer Zone at ni.com/zone. You can modify an example to fit an application, or you can copy and paste from one or more examples into a VI that you create. You also 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. To launch Chapter 2 Customizing a VI © National Instruments Corporation 2-13 Getting Started with LabVIEW 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. Displaying Data in a Table The table indicator displays generated data. Use the Build Table Express VI to build a table of generated data. Using the NI Example Finder Use the NI Example Finder to browse or search examples installed on your computer or on the NI Developer Zone at ni.com/zone. These examples demonstrate how to use LabVIEW to perform a wide variety of test, measurement, control, and design tasks. 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. Examples can show you how to use specific VIs or functions. 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. 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. Shortcuts This chapter introduced the following keyboard shortcuts. Note The <Ctrl> key in these shortcuts corresponds to the (Mac OS) <Option> or <Command> key or (Linux) <Alt> key. Shortcut Function <Ctrl-N> Opens a new, blank VI. <Ctrl-H> Shows or hides the Context Help window. (Mac OS) Press the <Command-Shift-H> keys. <Ctrl-B> Deletes all broken wires in a VI. <Ctrl-L> Displays the Error list window. © National Instruments Corporation 3-1 Getting Started with LabVIEW 3 Full and Professional: 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. Note The exercises in this chapter use Express VIs that are available only in the LabVIEW Full and Professional Development Systems. Building an Analysis VI In the following exercises, you will build a VI that generates a signal, filters the signal, indicates if the signal exceeds a certain limit, and records the data. After 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 40 minutes. Chapter 3 Full and Professional: Analyzing and Saving a Signal Getting Started with LabVIEW 3-4 ni.com 3. Double-click the Simulate Signal2 Express VI to display the Configure Simulate Signal dialog box. 4. Select Sine from the Signal type pull-down menu. 5. Enter 60 in the Frequency (Hz) text box. 6. Enter .1 in the Amplitude text box. 7. Place a checkmark in the Add noise checkbox to add noise to the sine signal. 8. Select Uniform White Noise from the Noise type pull-down menu. 9. Enter 0.1 in the Noise amplitude text box. 10. Enter -1 in the Seed number text box. 11. In the Timing section, select the Run as fast as possible option. 12. In the Signal Name section, remove the checkmark from the Use signal type name checkbox. 13. Enter 60 Hz and Noise in the Signal name text box. When you change the signal name in the Configure Simulate Signal dialog box, LabVIEW changes the name of the signal output on the block diagram. Changing the signal name makes it easier for you to identify the signal type when you view the Express VI on the block diagram. The Result Preview section displays a random signal. The Configure Simulate Signal dialog box should appear similar to Figure 3-2. Chapter 3 Full and Professional: Analyzing and Saving a Signal © National Instruments Corporation 3-5 Getting Started with LabVIEW Figure 3-2. Configure Simulate Signal Dialog Box 14. Click the OK button to save the current configuration and close the Configure Simulate Signal dialog box. Adding Two Signals To add two signals together to create one signal, you can use the Formula Express VI. Rather than merging two signals on one graph, the Formula Express VI adds both signals together to create a single signal on the graph. You can use this Express VI to add noise to a signal. Complete the following steps to add the 60 Hz and Noise signal to the Sine signal. 1. On the block diagram, triple-click the wire that connects the Sine output of the Simulate Signal Express VI to the Signals input of the Amplitude and Level Measurements Express VI and to the Unfiltered Signal indicator and remove the wire. 2. Click the Search button on the Functions palette to search for the Formula Express VI. and place it on the block diagram between the Chapter 3 Full and Professional: Analyzing and Saving a Signal Getting Started with LabVIEW 3-6 ni.com Simulate Signal Express VIs and the Amplitude and Level Measurements Express VI. 3. The Configure Formula dialog box appears in the Label column. Change the label for X1 to Sine and the label for X2 to 60 Hz and Noise. 4. Click the Input and + buttons to add Sine and 60 Hz and Noise together in the String text box. 5. Click the OK button to save the current configuration and close the Configure Formula dialog box. 6. Use the Wiring tool to wire the Sine output of the Simulate Signal Express VI to the Sine input of the Formula Express VI. 7. Wire the 60 Hz and Noise output of the Simulate Signal2 Express VI to the 60 Hz and Noise input of the Formula Express VI. 8. Wire the Result output of the Formula Express VI to the Unfiltered Signal indicator and to the Signals input of the Amplitude and Level Measurements Express VI. 9. Display the front panel by pressing the <Ctrl-E> keys. 10. Run the VI. The signal with added noise appears in the graph. 11. Click the STOP button to stop the VI. 12. Select File»Save As and save the VI as Analysis.vi in an easily accessible location. Filtering a Signal You can use the Filter Express VI to process signals through filters and windows. Complete the following steps to configure the Filter Express VI to filter the signal using an infinite impulse response (IIR) filter. 1. Remove the wire that connects the Result output of the Formula Express VI to the Signals input of the Amplitude and Level Measurements Express VI. 2. Remove all broken wires that result from removing the wire. 3. Search for the Filter Express VI and place it on the block diagram between the Simulate Signal2 Express VI and the Amplitude and Level Measurements Express VI. The Configure Filter dialog box appears. 4. In the Filter Specifications section, change the Cutoff Frequency (Hz) to 25. Chapter 3 Full and Professional: Analyzing and Saving a Signal © National Instruments Corporation 3-9 Getting Started with LabVIEW 3. Place a checkmark in the Peak to peak checkbox. Peak to peak appears in the Results section with the corresponding value of the measurement. 4. 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 output, shown at left. You will use the Peak to Peak output in a later exercise. Controlling the Speed of Execution To plot the points on the waveform graphs 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. Search for the Time Delay Express VI. 2. Place the Time Delay Express VI in the lower left-hand corner of the While Loop. The Configure Time Delay dialog box appears. 3. Enter .1 in the Time delay (seconds) text box and click the OK button. 4. Run the VI. The loop iterates once every tenth of a second. Adding a Warning Light If you want a visual cue to indicate when a value exceeds a specified limit, you can 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 right-clicking any blank space on the front panel. 2. On the Express palette, select the LEDs palette, shown in Figure 3-4. Chapter 3 Full and Professional: Analyzing and Saving a Signal Getting Started with LabVIEW 3-10 ni.com Figure 3-4. LEDs Palette 3. Select the round LED indicator and place it on the front panel to the left of the waveform graphs. 4. Double-click the Boolean label above the LED and enter Warning to change the label of the LED. You will use this LED in a later exercise to indicate when a value has exceeded its limit. 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 LED to light, use the Comparison Express VI. Complete the following steps to compare the peak-to-peak value to a limit you set. 8. Search for the Comparison Express VI and place it to the right of the Amplitude and Level Measurements Express VI. The Configure Comparison dialog box appears. 9. In the Compare Condition section, select the > Greater option. 10. In the Comparison Inputs section, select Value and enter 2 in the Value text box to assign a constant value at which you want the LED to light. 11. Click the OK button to save the current configuration and close the Configure Comparison dialog box. Chapter 3 Full and Professional: Analyzing and Saving a Signal © National Instruments Corporation 3-11 Getting Started with LabVIEW 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. 12. Wire the Peak to Peak output of the Amplitude and Level Measurements Express VI to the Operand 1 input of the Greater Express VI. 13. Move the cursor over the wire that connects the Peak to Peak output to the Operand 1 input. 14. 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 LED to light, you must wire the LED 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. Chapter 3 Full and Professional: Analyzing and Saving a Signal Getting Started with LabVIEW 3-14 ni.com 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 in the LabVIEW Data directory with a spreadsheet or text-editing application. The file has a header which contains information about the Express VI. 6. Close the file after you finish looking at it and return to the Save Data VI. Adding a Button That Stores Data When Clicked 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. Search the Controls palette for the rocker button. Select one of the rocker buttons and place it to the right of the waveform graphs. 2. Right-click the rocker button and select Properties from the shortcut menu to display the Boolean Properties dialog box. 3. Change the label of the button to Write to File. 4. 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. 5. Click the OK button to save the current configuration and close the Boolean Properties dialog box. 6. 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. Chapter 3 Full and Professional: Analyzing and Saving a Signal © National Instruments Corporation 3-15 Getting Started with LabVIEW 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. 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 replace the Comment input with the Enable input. 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. 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 3-6. Figure 3-6. Block Diagram of the Save Data VI Chapter 3 Full and Professional: Analyzing and Saving a Signal Getting Started with LabVIEW 3-16 ni.com 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. Close the file after you finish looking at it. 5. Save and close the VI. © National Instruments Corporation 4-1 Getting Started with LabVIEW 4 Hardware: 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»Getting Started with DAQ»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. The following exercises require that you have NI-DAQmx and an NI-DAQmx-supported device. Refer to the NI-DAQ Readme for the list of NI-DAQmx-supported devices. If you have a device that is supported only with Traditional NI-DAQ, 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. Note With NI-DAQmx 7.4 or later you can create NI-DAQmx simulated devices in MAX. An NI-DAQmx simulated device is a software replica of a DAQ device. Refer to the Measurement & Automation Explorer Help for NI-DAQmx for detailed instructions on creating an NI-DAQmx simulated device that you can use to complete the following exercises. Chapter 4 Hardware: Acquiring Data and Communicating with Instruments Getting Started with LabVIEW 4-2 ni.com 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. 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, display the Functions palette and select Express»Input to display the Input 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. 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. Chapter 4 Hardware: Acquiring Data and Communicating with Instruments © National Instruments Corporation 4-3 Getting Started with LabVIEW 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. Chapter 4 Hardware: Acquiring Data and Communicating with Instruments Getting Started with LabVIEW 4-6 ni.com 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. In the following exercises, you will communicate with an instrument. Finding and Installing Instrument Drivers (Windows and Linux) Use the NI Instrument Driver Finder to search for and install LabVIEW Plug and Play instrument drivers without leaving the LabVIEW development environment. Note The Instrument Driver Finder is available only on Windows and Linux. You must have Internet access to use the Instrument Driver Finder. You also can visit the NI Instrument Driver Network at ni.com/idnet to find a driver for an instrument. Chapter 4 Hardware: Acquiring Data and Communicating with Instruments © National Instruments Corporation 4-7 Getting Started with LabVIEW Complete the following steps to search for and install an instrument driver using the Instrument Driver Finder. 1. Select Tools»Instrumentation»Find Instrument Drivers or Help» Find Instrument Drivers to launch the Instrument Driver Finder. 2. Select National Instruments from the Manufacturer pull-down menu. 3. Click the Search button. The folders on the Search Results page represent instrument drivers, and the contents of the folders represent the files that the Instrument Driver Finder can download and install. The Instrument Driver Finder opens the first driver folder in the list and selects a driver file. You can click different files and use the detailed information to the right to choose the correct driver for the instrument. 4. Select the first instrument driver file from the Driver list and click the Install button. 5. If you do not have an NI.com profile, select No, I Need to create a profile and click the Create Profile button to open a browser window in which you can create an NI.com profile. If you do have an NI.com profile, skip to step 7. 6. Create a profile and return to the Instrument Driver Finder. 7. Select Yes, fill in your email address and ni.com password, and click the Login button. 8. Click the Close button after the Instrument Driver Finder downloads and installs the instrument driver into the labview\instr.lib directory and displays the path to the newly installed driver. 9. Click the Close button to close the Instrument Driver Finder. You also can create your own instrument drivers. Refer to the Controlling Instruments»Using Instrument Drivers book on the Contents tab in the LabVIEW Help for more information about creating instrument drivers. Selecting an Instrument Using the Instrument I/O Assistant If a driver is not available for an instrument, you can use the Instrument I/O Assistant Express VI to communicate with the instrument. Note You must have the Instrument I/O Assistant installed to use the Instrument I/O Assistant Express VI. You install the Instrument I/O Assistant from the National Instruments Device Drivers CD. Complete the following steps to use the Instrument I/O Assistant Express VI to select an instrument. Chapter 4 Hardware: Acquiring Data and Communicating with Instruments Getting Started with LabVIEW 4-8 ni.com 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. In the Instrument I/O Assistant dialog box, click the Add Step button and click the Query and Parse step. 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 Chapter 4 Hardware: Acquiring Data and Communicating with Instruments © National Instruments Corporation 4-11 Getting Started with LabVIEW Instrument Drivers Use the NI Instrument Driver Finder to search for and install LabVIEW Plug and Play instrument drivers without leaving the LabVIEW development environment. 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. Refer to the Controlling Instruments»Using Instrument Drivers book on the Contents tab in the LabVIEW Help for more information about the Instrument Driver Finder. You also can visit the NI Instrument Driver Network at ni.com/idnet to find a driver for an instrument, or you can create your own instrument drivers. Refer to the Controlling Instruments»Using Instrument Drivers book on the Contents tab in the LabVIEW Help for more information about creating instrument drivers. Instrument I/O Assistant Express VI 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. © National Instruments Corporation 5-1 Getting Started with LabVIEW 5 Using Other LabVIEW Features 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. Chapter 5 Using Other LabVIEW Features Getting Started with LabVIEW 5-4 ni.com 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. • Programmatically control properties and methods for the LabVIEW environment, VIs, and controls and indicators—You can control programmatically 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»Programmatically 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. • Share data within an application or across a network—You can create configured software items called shared variables to share data among VIs or between locations in an application that you cannot connect with wires. 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. Chapter 5 Using Other LabVIEW Features © National Instruments Corporation 5-5 Getting Started with LabVIEW • 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 must use a project to build applications and shared libraries. You also must use a project to work with an RT, FPGA, PDA, Touch Panel, DSP, or embedded target. Refer to the specific module documentation for more information about using projects with these targets. 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. • Access other Windows applications—You can use LabVIEW as a .NET or ActiveX client to access the objects, properties, methods, and events associated with .NET server or ActiveX applications. Refer to the Fundamentals»Windows Connectivity book on the Contents tab in the LabVIEW Help for more information about these features. • Write mathematical formulas, equations, and scripts—You can use various nodes to perform mathematical operations on the block diagram. You also can use the LabVIEW MathScript text-based language to write mathematical functions and scripts. Refer to the Fundamentals»Formulas and Equations book on the Contents tab in the LabVIEW Help for more information about these features. © National Instruments Corporation G-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. Glossary Getting Started with LabVIEW G-2 ni.com 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. Glossary © National Instruments Corporation G-3 Getting Started with LabVIEW 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 IEEE 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. DC Direct current. 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. dynamic data type Data type used by Express VIs that includes the data associated with a signal and attributes that provide information about the signal, such as the name of the signal or the date and time LabVIEW acquired the data. Attributes specify how the signal appears on a graph or chart. Glossary Getting Started with LabVIEW G-6 ni.com 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. 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. Glossary © National Instruments Corporation G-7 Getting Started with LabVIEW project A collection of LabVIEW files and non-LabVIEW files that you can use to create build specifications and deploy or download files to targets. Project Explorer window Window in which you can create and edit LabVIEW projects. Properties dialog boxes Dialog boxes accessed from the shortcut menu of a control or indicator that you can use to configure how the control or indicator appears in the front panel window. 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. 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, While Loop, or Timed Loop. subpalette Palette that you access from another palette that is above the subpalette in hierarchy. subVI VI used on the block diagram of another VI. Comparable to a subroutine. Glossary Getting Started with LabVIEW G-8 ni.com T .tdm file Binary measurement file that contains waveform data. .tdms file TDM Streaming file. Binary file that provides faster writing perfomance than the .tdm file format and allows a simpler interface for defining properties. 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. template VI VI that contains common controls and indicators from which you can build multiple VIs that perform similar functions. Access template VIs from the New dialog box. 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. 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). © National Instruments Corporation I-1 Getting Started with LabVIEW Index Symbols .lvm files, 3-13, 3-17 .tdm files, 3-17 .tdms files, 3-17 A acquiring information for instruments, 4-8 signals, 4-1 Acquiring a Signal VI block diagram (figure), 1-14 adding channels to tasks, 4-5 controls from the block diagram, 2-5 controls to the front panel, 1-5 graph indicators, 2-5 inputs to Express VIs, 1-8, 2-4, 3-15 multiple signals, 3-5 numeric indicators, 2-4 signals, 3-3 visual cues on front panel, 3-9 warning lights, 3-9 Amplitude and Level Measurements Express VI, 3-2 analyzing voltage, 3-8 analyzing signals, 3-8 applications building, 5-5 communicating with across networks, 5-4 Arithmetic & Comparison palette, 1-11 B blank VIs, 2-2 block diagram, 1-5, 1-19 customizing, 2-12 indicators, 3-17 placing objects from help, 2-11 showing, 1-7 broken Run button, 2-7 wires, 2-7, 2-13 Build Table Express VI, 2-8 building applications, 5-5 shared libraries, 5-5 VIs, 1-1 buttons adding, 3-14 Run, 1-5 C calling code from text-based languages, 5-4, 5-5 changing signal types, 1-7 channels, 4-2 adding to tasks, 4-5 renaming, 4-4 communicating with instruments, 4-6 with LabVIEW applications across networks, 5-4 Comparison Express VI, 3-10 configuration dialog boxes, 1-19 configuring controls, 1-20 indicators, 1-20 Context Help window, 2-2, 2-11, 3-2 button, 2-2, 3-2 displaying configuration of Express VIs, 3-2 displaying errors, 2-13 Index Getting Started with LabVIEW I-2 ni.com figure, 2-2 showing, 2-2 controlling execution speed, 2-8 VIs programmatically, 5-4 controls, 1-18, 3-17, 5-1 adding from the block diagram, 2-5 adding to the front panel, 1-5 configuring, 1-20 creating, 2-5, 2-12 customizing, 1-15 data types, 5-3 numeric, 5-1 palette, 1-5 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, 2-5, 2-12 graph indicators, 2-5 indicators, 2-12 NI-DAQmx tasks, 4-2 customizing block diagrams, 2-12 controls, 1-15 front panels, 2-4 indicators, 1-17 menus, 5-5 simulated signals, 3-3 D DAQ Assistant Express VI, 4-2, 4-10 DAQ devices, 4-2 data displaying from DAQ devices, 4-4 in tables, 2-8, 2-13 graphing from DAQ devices, 4-4 saving to a file, 3-13 when prompted by a user, 3-14 storing, 3-14 data flow, 1-9, 1-14, 1-19 data types dynamic, 5-3 overview, 5-3 deleting wires, 1-11 deselecting objects, 1-9 displaying data from DAQ devices, 4-4 data in tables, 2-8, 2-13 errors in Context Help window, 2-13 signals in a graph, 1-14 documentation conventions used in this manual, ix introduction to this manual, ix NI resources, A-1 drivers instrument, 4-6 NI resources, A-1 dynamic data, 5-3 converting from and to, 5-3 E Error list window, 2-7, 2-12 errors, 2-12 displaying in Context Help window, 2-13 list, 2-7, 2-12 window, 2-7, 2-12 example VIs NI Example Finder, 2-10 NI resources, A-1 Execution Control palette, 2-6 execution speed, controlling, 2-8 Express VIs, 1-19 Amplitude and Level Measurements, 3-2, 3-8 Index © National Instruments Corporation I-3 Getting Started with LabVIEW Build Table, 2-8 Comparison, 3-10 configuration dialog boxes, 1-19 Convert from/to Dynamic Data, 5-3 DAQ Assistant, 4-2, 4-10 Filter, 3-6 Formula, 1-11 inputs, 1-20 Instrument I/O Assistant, 4-7, 4-11 Scaling and Mapping, 1-11 Simulate Signals, 1-7 Time Delay, 2-8 Write To Measurement File, 3-13, 3-17 F files grouping, 5-5 saving to other formats, 5-4 Filter Express VI, 3-6 Formula Express VI, 1-11, 3-5 front panel, 1-5, 1-18 Acquiring a Signal VI (figure), 1-2 adding controls, 1-5 visual cues, 3-9 controls, 1-18, 3-17 customizing, 2-4 indicators, 1-19 modifying, 2-7 showing, 1-10 Warning Light VI (figure), 3-2 functions, 5-2 Merge Signals, 1-14, 2-5 Functions palette figure, 1-11 showing all categories, 5-2 G Getting Started window, 1-4, 3-2 figure, 1-3 graph indicators, creating, 2-5 graphing data from DAQ devices, 4-4 two signals, 1-14 grouping files, 5-5 H help Context Help window, 2-2, 2-11, 3-2 LabVIEW Help, 1-11, 1-20, 2-11 searching, 2-3, 2-10, 2-11 LabVIEW resources, 1-20, 2-11 searching, 2-3, 2-10, 2-11 technical support, A-1 I indicators, 1-19, 3-17, 5-1 adding numeric, 2-4 configuring, 1-20 creating, 2-12 customizing, 1-17 data type, 5-3 numeric, 5-1 removing, 2-7 Input palette, 2-2 inputs, Express VI, 1-20 Instrument Driver Network, 4-6 instrument drivers, 4-6, 4-11 finding, 4-11 installing, 4-11 NI resources, A-1 Instrument I/O Assistant Express VI, 4-7, 4-11 instruments acquiring information, 4-8 communicating, 4-6 parsing information, 4-8 selecting, 4-7 introduction to this manual, 1-ix