1、 Expanding the Features of a VI You can choose one of many LabVIEW VI templates to use as a starting point. However, sometimes you need to build a VI for which a template is not available. This chapter teaches you how to build and customize a VI without using a template. Building a VI from a Blank T
2、emplate In the following exercises, you will open a blank VI and add Express VIs and structures to theblock diagram to build a new VI. You will build a VI that generates a signal, reduces the number of samples in the signal, and displays the resulting data in a table on the front panel. When you com
3、plete 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 approximately 30 minutes. Figure 3-1. Front Panel for the Reduce Samples VI Opening a Blank VI If no template is available for the task you want to create, you can sta
4、rt with a blank VI and add Express VIs to accomplish the specific task. Complete the following steps to open a blank VI. 1. In the LabVIEW dialog box, click the arrow on the New button and select BlankVI from the shortcut menu or press the keys to open a blank VI. Notice that a blank front panel and
5、 block diagram appear. 1 Note You also can open a blank VI by selecting Blank VI from the Create new list in The New dialog box or by selecting FileNew VI from the front panel or block diagram menu bar. 2. If the Functions palette is not visible, right-click any blank space on the block diagram to b
6、ring up the temporary version of the Functions palette. Click the thumbtack, shown at left, in the upper left corner of the Functions palette to place the palette on the screen. Note You can right-click on a blank space on the block diagram or the front panel to bring up the Functions or Controls pa
7、lettes. Adding an Express VI that Simulates a Signal Complete the following steps to find the Express VI you want to use and then add it to the block diagram. 1. If the Context Help window is not visible, press the keys to open the Context Help window. You also can press the Show Context Help Window
8、 button, shown at left, to open the Context Help window. 2. Select the Input palette on the Functions palette and move the cursor over the Express VIs on the Input palette.Notice that the Context Help window displays information about the function of each Express VI. 3. From the information provided
9、 in the Context Help window, find theExpress VI that can output a sine wave signal. 4. Select the Express VI and place it on the block diagram. The Configure Simulate Signal dialog box appears. 5. Idle the cursor over the various options in the Configure Simulate Signal dialog box, such as Frequency
10、 (Hz), Amplitude, and Samples per second (Hz). Read the information that appears in the Context Help window. 6. Configure the Simulate Signal Express VI to generate a sine wave with a frequency of 10.7 and amplitude of 2. 7. Notice how the signal displayed in the Result Preview window changes to ref
11、lect the configured sine wave. 8. Close the Configure Simulate Signal dialog box. 9. Move the cursor over the Simulate Signal Express VI and read the information that 2 appears in the Context Help window.Notice that the Context Help window now displays the configuration of the Simulate Signal Expres
12、s VI. 10. Save this VI as Reduce Samples.vi to an easily accessible location. Modifying the 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. Select HelpVI, Function, & How-To Help to open the LabVIEW Help. 2.
13、Click the Search tab and type sample compression in the Type in the word(s) to search for text box. Notice that this word choice reflects what you want this Express VI to do compress, or reduce, the number of samples in a signal. 3. Select the Sample Compression Express VI topic to display the topic
14、 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, shown at left, to select the Express VI. 5. Move the cursor to the block diagram. Notice how LabVIEW attaches the Sample Compression Express VI to the
15、cursor. 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. Close the Configure Sample Compression dialog box. 9. Using
16、 the Wiring tool, wire the Sine output in the Simulate Signal Express VI to the Signals input in the Sample Compression Express VI. Customizing the Front Panel In the previous exercises, you added controls and indicators to the front panel using the Controls palette. You also can add controls and indicators from the block diagram. Complete the following steps to create controls and indicators.
