CH02 LABVIEW Graphical Programming

CH02 LABVIEW Graphical Programming - CHAPTER 2 LabVIEW...

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C H A P T E R 2 LabVIEW Graphical Programming Environment LabVIEW constitutes a graphical programming environment that allows one to design and analyze a DSP system in a shorter time as compared to text-based programming environments. LabVIEW graphical programs are called Virtual Instruments (VIs). VIs run based on the concept of data flow programming. This means that execution of a block or a graphical component is dependent on the flow of data, or more specifically a block executes when data are made available at all of its inputs. Output data of the block are then sent to all other connected blocks. Data flow programming allows multiple operations to be performed in parallel, since its execution is determined by the flow of data and not by sequential lines of code. 2.1 Virtual Instruments (VIs) A VI consists of two major components, which include a Front Panel (FP) and a Block Diagram (BD). An FP provides the user-interface of a program, whereas a BD incorporates its graphical code. When a VI is located within the block diagram of another VI, it is called a subVI. LabVIEW VIs are modular, meaning that any VI or subVI can be run by itself. 2.1.1 Front Panel and Block Diagram An FP contains the user interfaces of a VI shown in a BD. Inputs to a VI are represented by controls. Knobs, pushbuttons, and dials are a few examples of controls. Outputs from a VI are represented by indicators. Graphs, LEDs (light indicators), and meters are a few examples of indicators. As a VI runs, its FP provides a display or user interface of controls (inputs) and indicators (outputs). 5
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A BD contains terminal icons, nodes, wires, and structures. Terminal icons are interfaces through which data are exchanged between an FP and a BD. They correspond to controls or indicators that appear on an FP. Whenever a control or indicator is placed on an FP, a terminal icon gets added to the corresponding BD. A node represents an object which has input and/or output connectors and performs a certain function. SubVIs and functions are examples of nodes. Wires establish the flow of data in a BD. Structures are used to control the flow of a program such as repetitions or conditional executions. Figure 2-1 shows what an FP and a BD window look like. 2.1.2 Icon and Connector Pane A VI icon is a graphical representation of a VI. It appears in the top right corner of a BD or an FP window. When a VI is inserted in a BD as a subVI, its icon gets displayed. A connector pane defines inputs (controls) and outputs (indicators) of a VI. The number of inputs and outputs can be changed by using different connector pane patterns. In Figure 2-1 , a VI icon is shown at the top right corner of the BD and its corresponding connector pane having two inputs and one output is shown at the top right corner of the FP.
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