File Writer VI

Summary: In this exercise, the objective is to write data to a file. Complete the following steps to build a VI that concatenates a message string, a numeric value, and a unit string to a file. In another exercise, you will build a VI that reads the file and displays its contents.

EXERCISE 1

1.A) Front Panel

1. Open a blank VI and build the front panel shown in Figure 1.

   Figure 1

   1. Place a path indicator located on the Controls>>Text Indicators palette on the front panel. This indicator displays the path for the data file you create.
   2. Right-click the String to Write control and select Visible Items>>Scrollbar from the shortcut menu to display a scrollbar.

1.B) Block Diagram

1. Build the block diagram shown in Figure 2.

   Figure 2

   1.  Place the Create String VI from the previous exercise on the block diagram. Select Functions>>All Functions>>Select a VI and navigate toC:\Exercises\LabVIEW Basics I\Create String.vi. This subVI concatenates the three input strings to one combined string.
   2.  Place the Open/Create/Replace File VI, located on the Functions>>All Functions>>File I/O palette, on the block diagram. This VI displays a dialog box to open or create a file. Right-click the prompt input, select Create>>Constant from the shortcut menu, and type Enter Filename in the constant. When the VI runs, a file navigation dialog box appears with Enter Filename as the title of the window. Right-click the function input, select Create>>Constantfrom the shortcut menu, and click the constant with the Operating tool to select create or replace.
   3.  Place the Write File function, located on the Functions>>All Functions>>File I/O palette, on the block diagram. This function writes the concatenated strings to the file.
   4.  Place the Close File function, located on the Functions>>All Functions>>File I/O palette, on the block diagram. This function closes the file.
   5.  Place the Simple Error Handler VI, located on the Functions>>All Functions>>Time & Dialog palette, on the block diagram. This function checks the error cluster and displays a dialog box if an error occurs.
   6. Complete the block diagram as shown in Figure 2.
2. Save the VI as File Writer.vi in the C:\Exercises\LabVIEW Basics I directory.

1.C) Run the VI

1. Enter values in the front panel controls and run the VI. An Enter Filename dialog box appears.
2. Type demofile.txt and click the Save or OK button to save the file. The VI writes the String to Write, Numeric to Write, and Unit to Write values to the file.
3. Close the VI.

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