Introduction to benchtop equipment and data acquisition  (Page 6/6)

20. For both output terminals on the Tone Measurements icon, right click and select Create>>Numeric Indicator to create Front Panel displays of theseparameters.

21. Your block diagram should now be similar to Figure 9.

22. There are several Express VIs in the Signal Analysis palette that are similar to the Tone Express VI.These other Express VIs display information regarding frequency content, DC offset, curve fitting, etc. Depending on time, you maywant to experiment with these other functions.

3.4 displaying data on-screen

One of the strengths of LabVIEW is the ease with which user interfaces are developed. In this section we willdevelop an on-screen graph display.

23. Right-click on the wire between the DAQ Assistant and the Tone Measurements icons. SelectCreate>>Graph Indicator.

24. Display the Front Panel by pressing<Ctrl-E>. You should see that a graph has been created on the Front Panel.

3.5 writing data to a file

Now that the VI can acquire data, we will develop a means to write the data to an Excel file and display thedata onscreen. We will use the“Write to Measurement File”Express VI.

25. Right click on the Block Diagram to bring up the Functions Palette.

26. If you can’t find the“Write to Measurement File”Express VI, click on the search button at the top of the Functions Palette. Type“write to file”and double click the choice that ends in<<file I/O>>. The search menu will change into the Functions Palette, and the“Write to Measurement File”Express VI will be highlighted. Place this Express VI on the block diagram.

27. Configure the window as shown in Figure 11. Configure the File Name window to contain thepath to wherever you wish to store your data. Change the Segment Headers to OneHeader Only and the X Value Columns to One Column Only. Click OK.

28. Place your cursor over the data output terminal on the DAQ assistant icon. The cursor should change to awire spool. Click on the data terminal and connect the wire to the signals inputterminal on the Write to File icon.

29. Right click the File Name terminal input on the Write to File icon. Select Create>>Control. This creates a field on the Front Panel where the user can enter thename of the data file that will be created.

30. Create a write disable button by right-clicking on the front panel. Click Boolean>>Push Button. Type“Store Data”to change the name of the control.

31. On the block diagram, connect the push button to the Enable terminal on the Write to File icon. (When thiscontrol is enabled, the program will write data to the file-path indicated on the Front Panel.)

32. Your Block Diagram should now be similar to Figure 12.

3.6 running the vi

33. On the Front Panel, click the Run button. You should see the signal from the function generator displayed onthe graph.

34. When you enable data storage, a .lvm file should will be created in your folder. On the Windows desktop, openyour group’s folder. Right click on the .lvm file that you just made and select Open With>>Microsoft Office Excel.

35. Plot the data and compare it to the graph shown on the front panel. You may want save screen shots or makehard-copies of any plots to include in your lab book.

Part 4: shutting down

After you have saved any data you want to keep, close all programs and log off of the computer. Turn off theCompactDAQ chassis, the function generator, and the oscilloscope. Take time to clean up your work area. Ten percent of your lab bookgrade will be based on cleanliness.

Lab report

You are to submit a one-page memo report describing what you learned from the lab. See the Lab 1 WritingAssignment handout for more details.