There are three steps to create our application in the software environment:
A virtual instrument (VI) has three main components—the front panel, the block diagram and the icon/connector pane. In order to use a VI as a subVI in the block diagram of another VI, it is essential that it contains an icon and a connector. The two LabVIEW windows are the front panel (containing controls and indicators) and block diagram (containing terminals, connections and graphical code). The front panel is the user interface of the virtual instrument. The code is built using graphical representations of functions to control the front panel objects. The block diagram contains this graphical source code. In LabVIEW, you build a user interface or front panel with controls and indicators. Controls are knobs, push buttons, dials and other input devices. Indicators are graphs, LEDs and other displays. After you build the user interface, you can add code using VIs and structures to control the front panel objects. The block diagram contains this code. In some ways, the block diagram resembles a flowchart.
When you open a new or existing VI, the front panel of the VI appears. The front panel is the interactive user interface for the VI. It is named a front panel because it stimulates the front panel of a physical instrument. Build the front panel with controls and indicators as shown in Figure 2.1.
One of the most powerful features that LabVIEW offers engineers and scientists is its graphical programming environment to design custom virtual instruments by creating a graphical user interface on the computer screen to
Figure: LabVIEW virtual instrument front panel.
The front panel can include knobs, push buttons, graphs and various other controls (which are user inputs) and indicators (which are program outputs). Controls are inputs used to simulate instrument input devices and supply data to the block diagram of the VI, and indicators are outputs displays used to simulate instrument output devices and display data the block diagram acquires or generates. The front panel is customized to emulate control panels of traditional instruments, create custom test panels, or visually represent the control and operation of processes.
The block diagrams accompany the program for the front panel. Front panel objects appear as terminals on the block diagram and the components wired together. After the front panel is built, codes are added using graphical representations of functions in the block diagram to control the front panel objects. The block diagram contains the graphical source code composed of nodes, terminals, and wires. The block diagram is the actual executable program as shown in Figure 2.2.
The components of a block diagram are lower-level VIs, built-in functions, constants and program execution control structures. Wires have to be drawn to connect the corresponding objects together to indicate the flow of data between each of them. Front panel objects have analogous terminals on the block diagram so that data can pass easily from the user to the program and back to the user. Use Express VIs, standard VIs and functions on the block diagram to create our measurement code. Block diagram objects include the terminals, subVIs, functions, constants, structures and wires. LabVIEW is the easiest, most powerful tool for acquiring, analyzing and presenting real-world data. Terminals are entry and exit ports that exchange information between the panel and the diagram. Terminals are analogous to parameters and constants in text-based programming languages. Right-click the block diagram objects and select View As icon to change the icon view.
Figure: LabVIEW virtual instrument block diagram.
To use a VI as a subVI, it must have an icon and a connector pane. Every VI displays an icon in the upper-right corner of the front panel and block diagram windows. An icon is a graphical representation of a VI. The icon can contain both text and images. To use a VI as a subVI, you need to build a connector pane. The connector pane is a set of terminals that correspond to the controls and indicators of that VI.
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