If you wire to an optional terminal when the subVI is expanded, then resize the subVI so the optional terminal no longer appears in the expanded field, the optional terminal appears as an input or output arrow in the colored field. However, if you unwire the optional terminal, the input or output arrow does not appear. By default, inputs appear above outputs when you expand the subVI.
A line divides inputs from outputs in the shortcut menu. Labels for expandable subVIs appear in the colored field that surrounds the icon. To resize the expandable node so that it accommodates the name of each terminal on a single line in the expandable field, right-click the subVI and select Size to Text from the shortcut menu. SubVI created with default icon is shown in Figure 3. An icon for the new subVI replaces the selected section of the block diagram.
LabVIEW creates controls and indicators for the new subVI, automatically configures the connector pane based on the number of control and indicator terminals you selected, and wires the subVI to the existing wires.
Creating a subVI from a selection is convenient but still requires careful planning to create a logical hierarchy of VIs. Consider which objects to include in the selection and avoid changing the functionality of the original or resulting VI.
Creating a subVI from a selection is the same as removing the selected objects and replacing them with a subVI. The front panel terminals remain on the front panel of the original VI and the terminals are wired to the new subVI. Also for each front panel object with a Property Node or local variable in the selection, LabVIEW adds a control reference to the original block diagram and wires the reference to the subVI.
You avoid creating cycles on the block diagram and including a structure that contains a front panel terminal in the selection. The subVI controls and indicators receive data from and return data to the block diagram of the calling VI.
Complete the following steps to open a subVI and edit it. Step 1: Use the operating or positioning tool to double-click the subVI on the block diagram. Step 2: Edit the subVI. Step 4: Navigate to and double-click the VI you want to use as a subVI, and place it on the block diagram. Step 5: Wire the subVI terminals to other nodes on the block diagram.
LLB files end with the extension. National Instruments recommends that we save VIs as individual files, organized in directories, especially if multiple developers are working on the same project.
In order to deploy the application, you first prepare the code, create an Application Exe Build Specification, and then create an Installer Build Specification. Installers are used to distribute the stand-alone application. To create a professional, stand-alone application with VIs, you must consider several programming issues. First, know what outside code your applications uses. For example, do you call any system or custom DLLs or shared libraries?
Another issue is the path names you use in the VI. Assume you read data from a file during the application, and the path to the file is hard-coded on the block diagram. Once an application is built, the file is embedded in the executable, changing the path of the file. Being aware of these issues will help you build more robust applications in the future.
Another issue that affects the application you have currently built is that the top-level VI does not quit LabVIEW or close the front panel when it is finished executing. Stand-alone applications: Use stand-alone applications to provide other users with executable versions of VIs. Windows Applications have a. Mac OS Applications have a.
Installers Windows : Use installers to distribute stand-alone applications, shared libraries, and source distributions that you create with the Application Builder. A build specification contains all the settings for the build, such as files to include, directories to create and settings for directories of VIs. Define connections by assigning a front panel control or indicator to each of the connector pane terminals using the wiring tool.
When you move the cursor over a VI icon, the Context Help window displays this description and indicates which terminals are required, recommended or optional. When you move the cursor over controls and indicators, the Context Help window displays this description. The Application Builder is available in the Professional Development Systems or as an add-on package. Solution The front panel and the block diagrams for the half adder is shown in Figures P3.
Solution To find the decimal equivalent of a binary number, first create the front panel and the block diagram as given in Figures P3. Figure P3. Modular Programming 61 Figure P3. Solution Create the front panel and the block diagram as given in Figure P3. Find both the values of the roots and the nature of the roots. Solution Create the front panel and the block diagram as shown in Figures P3. Solution The block diagram to find the average of two numbers and convert a section of a VI into a subVI by selecting that portion is shown in Figures P3.
This VI uses a subVI for finding the trigonometric values. The SubVI consists of functions for converting degree values to radians and functions to find the sine, cosine and tangent values separately.
What is modular programming? Explain the need of icon and connector pane. What is a default icon and a custom icon? Consider an example and explain the steps involved in creating, saving and retrieving subVI? Explain how to create setting required, recommended, and optional inputs and outputs in creating terminals of a SubVI. What is the difference between viewing subVIs as icons and expandable nodes? How to create a subVI from the portion of an available VI? How can a stand-alone application be created?
How can subVI be displayed as expandable nodes? Create a VI that takes a number representing Celsius and converts it to a number representing Fahrenheit. Build the subVI. Build a subVI of the VI that accepts a user name and password and checks for a match in a table of information of two employees. If the name and password match, the confirmed name and a verification Boolean object are returned.
Create a subVI to compute the average of five students marks. Given the length and breadth, build a subVI to compute the area of the polygon. Build a subVI to calculate the gross salary, given the basic salary as input. Create a subVI given two inputs x and y, and compute the complex number, its complex conjugate and polar components.
Build a subVI to convert radians to degrees. Repetition and loop are used to perform an action frequently with variations in the details each time. These loops are used to control repetitive operations. Structures on the block diagram are used to repeat blocks of code and to execute code conditionally or in a specific order.
This chapter introduces the loops in LabVIEW, iterative data transfer in loops and timing a loop along with functions commonly used with these structures, including the shift register and the Feedback Node. Figure 4. Select the For Loop from the palette and use the cursor to drag a selection rectangle to create a new For Loop or around the section of the block diagram you want to repeat. Set the count explicitly by wiring a value from outside the loop to the left or top side of the count terminal, or set the count implicitly with auto-indexing.
Auto-indexing is explained in chapter 5. A VI will not run if it contains a For Loop that does not have a numeric value wired to the count terminal.
The iteration count always starts at zero. During the first iteration, the iteration terminal returns 0. Both the count and iteration terminals are bit signed integers. If you wire a floating-point number to the count terminal, LabVIEW rounds it and coerces it to within range. If you wire 0 or a negative number to the count terminal, the loop does not execute and the outputs contain the default data for that data type.
A For Loop can only execute an integer a number of times. Example 4. Repetition and Loops 67 Figure 4. Solution: The front panel of this VI consists of a Numeric Control for providing number of iterations and a Framed Color Box for displaying various colors as shown in the figure. In the block diagram the function RGB to Color is used to produce various colors based on the combination of values given to the red, green and blue terminals.
As given in the solution, the For Loop will execute for three iterations. The value of the iteration terminal added with 1 is given as input for one of the terminals of multiplication functions for each iteration. The iteration value is multiplied with 50, and for producing red, green and blue values respectively.
These values are given to the RGB to Color function. This RGB to Color function produces three different colors based on the red, green and blue values. The produced colors are displayed in the framed Color Box indicator. The For Loop will execute only for three iterations since the number of iterations is set to 3. The number of iterations can be increased to produce more numbers of colors.
The While Loop always executes at least once. A While Loop stops executing the subdiagram, only if the expected value at the conditional terminal exists. These are called pre- and post-test modes. In the pre-test mode the condition is tested prior to the execution of every iteration and if the result is false, then the execution of the loop is aborted. In the post-test mode the test is carried out only at the end of the loop.
Functionally, the major difference is that under the post-test mode even if the condition is false at the first execution or first iteration, the loop will be executed at least once, since the test is only performed at the end of the loop. The While Loop executes the subdiagram until the conditional terminal, and receives a specific Boolean value.
The default behavior and appearance of the conditional terminal is Stop if True as shown in Figure 4. You can change the behavior and appearance of the conditional terminal by right-clicking the terminal or the border of the While Loop and selecting Continue if True from the shortcut menu as shown in Figure 4. You also can use the Operating Tool to click the conditional terminal to change the condition.
The VI shows error if the conditional terminal is unwired. You also can perform basic error handling using the conditional terminal of a While Loop. Error clusters are explained in Chapter 6 in detail.
The block diagrams shown in Figures 4. A random number is generated and displayed for each iteration in the Numeric Indicator in the Front Panel. In the block diagram shown in Figure 4. When the iteration value becomes 9, the conditional terminal receives a FALSE state and stops executing the loop.
Use the conditional terminal Stop if True as in Figure 4. Solution: The front panel consists of a Numeric Indicator to display the numbers. When the iteration value reaches 9, the conditional terminal receives a TRUE state and stops the execution of the While Loop. The iteration value is added with 1 to produce output from 1 to 10 and it is displayed in the Numeric Indicator. Tunnels feed data into and out of structures. The tunnel appears as a solid block on the border of the loop. The block is the color of the data type wired to the tunnel.
Data passes out of a loop after the loop terminates. When a tunnel passes data into a loop, the loop executes only after data arrives at the tunnel. In Figure 4. The value in the tunnel does not pass to the Iteration Number indicator until the While Loop has finished execution.
Only the last value of the iteration terminal displays in the Iteration Number indicator. Repetition and Loops 71 4. Outputs pass data out of a loop only after the loop completes all iterations. If you want the loop to check the value of a terminal for each iteration, place the terminal inside the loop.
When you place the terminal of a front panel Boolean control inside a While Loop and wire the terminal to the conditional terminal of the loop, the loop checks the value of the terminal for every iteration to determine if it must iterate. You can stop the While Loop as shown in Figure 4. If you place the terminal of the Boolean control outside the While Loop as shown in Figure 4. You also cause an infinite loop if the control outside the loop is set to TRUE and the conditional terminal is Continue if True.
Changing the value of the control does not stop the infinite loop because the value is only read once, before the loop starts. To stop an infinite loop, you must abort the VI by clicking the Abort Execution button on the toolbar. For example, you may have a VI that reads the temperature and displays it on a graph. If you want to display a running average of the temperature as well, you need to use data generated in previous iterations.
Two ways of accessing this data include the shift register and the feedback node. While Loops produce default data when the shift register is not initialized. For Loops produce default data if you wire 0 to the count terminal of the For Loop or if you wire an empty array to the For Loop as an input with auto-indexing enabled. The loop does not execute, and any output tunnel with auto-indexing disabled contains the default value for the tunnel data type.
Use shift registers to transfer values through a loop regardless of whether the loop executes. Shift registers are similar to static variables in text-based programming languages.
A shift register appears as a pair of terminals, shown in Figure 4. The terminal on the right side of the loop contains an up arrow and stores data on the completion of an iteration.
LabVIEW transfers the data connected to the right side of the register to the next iteration. After the loop executes, the terminal on the right side of the loop returns the last value stored in the shift register.
Create a shift register by right-clicking the left or right border of a loop and selecting the Add shift register from the shortcut menu. A shift register transfers any data type and automatically changes to the data type of the first object wired to the shift register.
The data you wire to the terminals of each shift register must be the same type. You can add more than one shift register to a loop. If you have multiple operations that use previous iteration values within our loop, you can use multiple shift registers to store the data values from those different processes in the structure as shown in Figure 4. Repetition and Loops 73 4. Initialize a shift register by wiring a control or constant to the shift register terminal on the left side of the loop.
If you do not initialize the shift register, the loop uses the value written to the shift register when the loop last executed or the default value for the data type if the loop has never executed. Use a loop with an uninitialized shift register to run a VI repeatedly so that each time the VI runs, the initial output of the shift register is the last value from the previous execution. Use an uninitialized shift register to preserve state information between subsequent executions of a VI.
After the loop executes, the last value stored in the shift register remains at the right terminal. If you wire the right terminal outside the loop, the wire transfers the last value stored in the shift register. If you have multiple operations that use previous iteration values within a loop, use multiple shift registers to store the data values from those different processes in the structure as shown in Figure 4.
The For Loop executes five times. The shift register value is added with the subsequent numbers starting from 1 to 5. After five iterations of the For Loop, the shift register passes the final value 15 to the indicator and the VI stops.
Each time you run the VI, the shift register begins with a value of 0. The shift register is used without initialization. The first time you run the VI, the shift register begins with a value of 0, which is the default value for a bit integer.
After five iterations of the For Loop, the shift register passes the final value 15 to the indicator and ends. The next time you run the VI, the shift register begins with a value of 15, which was the last value from the previous execution. After five iterations of the For Loop, the shift register passes the final value 30 to the indicator.
If you run the VI again, the shift register begins with a value of 30, and so on. Uninitialized shift registers retain the value of the previous iteration until you close the VI. Stacked shift registers remember values from multiple previous iterations and carry those values to the next iterations.
This technique is useful for averaging data points. To create a stacked shift register, right-click the left terminal and select Add Element from the shortcut menu. Stacked shift registers, as shown in Figure 4. If you add one more element to the left terminal, the value from the last two iterations carry over to the next iteration, with the most recent iteration value stored in the top shift register.
The second terminal stores the data passed to it from the previous iteration. You can add more than two terminals in the shift register. If you add two more elements to the left terminal, the second terminal stores the data passed to it from the previous iteration and the bottom terminal stores the data passed to it from two iterations ago.
To replace a tunnel into a shift register, right-click the tunnel and select Replace with Shift Register. If no tunnel exists on the loop border opposite of the tunnel you right-clicked, LabVIEW automatically creates a pair of shift register terminals. If one or more than one tunnel exists on the loop border opposite of the tunnel you right-clicked, the mouse pointer will turn to the symbol of a shift register.
You can choose the particular tunnel which is to be converted as the shift register by clicking the mouse over that tunnel as shown in Figure 4. Repetition and Loops 75 4. To replace a shift register with a tunnel, right-click the shift register and select Replace with Tunnels. If you replace an output shift register terminal with a tunnel on a For Loop, the wire to any node outside the loop breaks because the For Loop enables auto-indexing by default as shown in Figure 4.
Right click the auto-indexed tunnel and select Disable Indexing on the tunnel to correct the broken wire. This problem does not occur in While Loops because auto-indexing is disabled by default in While Loops. The concept of auto-indexing is explained in Chapter 5 in detail. LabVIEW is easy for teams to use since you do not need prior programming experience. Also, the software provides convenience due to its cross-platform compatibility , allowing the use of the software with peers who may use different technologies.
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LabVIEW lets you automate tests to receive reliable results that you can organize. You can choose from an extensive catalog of algorithms including filters, mathematics, scripts and formats, signal processing, sound, and vibration, etc. The software can collect measurements from tests that are run with compatible hardware devices and the results can be stored in files. LabVIEW is easy for teams to use since you do not need prior programming experience.
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