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Express VIs

LabVIEW 2013 Help

Edition Date: June 2013

Part Number: 371361K-01

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An Express VI is a VI whose settings you can configure interactively through a dialog box. Express VIs appear on the block diagram as expandable nodes with icons surrounded by a blue field.

You can configure an Express VI by setting options in the configuration dialog box that appears when you place the Express VI on the block diagram. You can double-click the Express VI or right-click the Express VI and select Properties from the shortcut menu to reopen the configuration dialog box. You also can configure the Express VI by wiring values to terminals of the Express VI on the block diagram.

Parameters that you can configure for an Express VI from the configuration dialog box are called configurable parameters. Parameters that you can configure for an Express VI from the block diagram are called expandable parameters or expandable terminals. A parameter can be both configurable and expandable, which means you can configure it from both locations. The configuration you specify for an Express VI with the configurable parameters determines the expandable terminals that appear on the block diagram.

You can use Express VIs to perform common measurement tasks. You also can create and edit Express VIs to distribute to users for building applications easily. Use the Create or Edit Express VI dialog box, available by selecting Tools»Advanced»Create or Edit Express VI, to create an Express VI from an existing VI, from another Express VI, or from a blank VI.

Benefits of Using Express VIs

The primary benefit of Express VIs is their interactive configurability. Express VIs are useful when you want to give users a VI or library of VIs for building their own applications easily with minimal programming expertise.

The configurability of Express VIs provides an interactive way to determine settings for operations that the user might not fully understand. For example, you might need a digital filter for a signal, but a library containing dozens of filter VIs does not help you choose the correct filter response or help you decide which parameters most directly affect the specific signal. The Filter Express VI allows you to interactively select the type of filter, manipulate filter parameters, and view the filter response in different ways. You can preview the results of different filters and filter parameters directly on the signal in the configuration dialog box of the Express VI. After you run the Filter Express VI, the Express VI displays the new signal as default data in the configuration dialog box.

Another advantage of Express VIs is that separate instances of an Express VI function independently. When you place an Express VI on the block diagram, an instance of the Express VI is embedded in that particular block diagram. The settings that you select in the configuration dialog box affect only that instance of the Express VI. If you place a standard VI in five different areas on the same block diagram, the result is five exact copies of the VI. The source code, default values, and front panel remain the same for all five copies. However, if you place an Express VI in five areas on a block diagram, the result is five separate Express VIs with different names, all independently configurable. Each instance of an Express VI can include different numbers and types of expandable terminals. The Context Help window also updates with the different settings for each instance.

Caveats When Using Express VIs

Express VIs do not provide run-time interactive configuration for VIs. If you need run-time reconfiguration, build an application with a user interface that contains features similar to a configuration dialog box.

Express VIs are designed for ease of use. If you need an application to run with strict memory restrictions or high execution speeds, use standard VIs.


 

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