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TOPICS

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Lesson 3Troubleshooting and Debugging VIs

A. LabVIEW Help UtilitiesB. Correcting Broken VIsC. Debugging TechniquesD. Undefined or Unexpected DataE. Error Checking and Error Handling

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A. LabVIEW Help Utilities – Context Help

• Displays basic information about LabVIEW objects whenyou move the cursor over each object• Select Help»Show

Context Help, press<Ctrl-H> orclick the Show ContextHelp Window buttonon the toolbar

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A. LabVIEW Help Utilities – LabVIEW Help

• Detailed descriptions of most palettes, menus, tools, VIs,and functions and instructions for using LabVIEW features• Accessing the LabVIEW Help:

− Select Help»Search the LabVIEW Help− Use the Detailed help

link or button in theContext Help window

− Right-click an objectand select Help fromthe shortcut menu

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A. LabVIEW Help Utilities – NI Example Finder

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GOAL

Exercise 3-1Concept: Using Help

Become familiar with using the Context Help window, theLabVIEW Help, and the NI Example Finder.

5DISCUSSION

Exercise 3-1Concept: Using Help

• You are given a VI containing unfamiliar functions. How doyou determine the functionality in the block diagram?

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B. Correcting Broken VIs

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B. Correcting Broken VIs

Common Issues• Broken wire

− You wired a Boolean controlto a String indicator

− You wired a Numeric controlto a Numeric control

• A required block diagram terminal is unwired• A subVI is broken or you edited its connector pane after you

placed its icon on the block diagram of the VI

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C. Debugging Techniques

Your VI isn’t broken, but you are getting unexpected data orbehavior• Any unwired or hidden subVIs?• Incorrect default data being used?• Undefined data being passed?• Numeric representation correct?• Node execution order correct?

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C. Debugging Techniques –Execution Highlighting

• Use execution highlighting to watch the data flow throughthe block diagram• If the VI runs more slowly than expected, confirm that you

turned off execution highlighting in subVIs

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C. Debugging Techniques – Single Stepping

Single-step through the VI to view each action of the VI on theblock diagramSuspend the execution of a subVI to edit values of controlsand indicators, to control the number of times it runs, or to goback to the beginning of the execution of the subVI• Open subVI and select Operate»Suspend When Called

from the shortcut menu

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C. Debugging Techniques – Probes

• Use the Probe tool to observe intermediate datavalues and to check the error output of VIsand functions, especially those performing I/O• Retain the values in the wires so that you can

probe wires for data after execution has finished

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C. Debugging Techniques – Breakpoints

• When you reach a breakpoint during execution, the VIpauses and the Pause button appears red• You can take the following actions at a breakpoint:

− Single-step through execution using the single-steppingbuttons

− Probe wires to check intermediate values− Change values of front panel controls− Click the Pause button to continue running to the next

breakpoint or until the VI finishes running

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D. Undefined or Unexpected Data

• ∞ (Inf)− Infinity− Divided a number by zero?• NaN

− Not a number− Produced by invalid operations, such as taking the square root

of a negative number• Check for unexpected Inf values or NaN values in your

mathematical operations

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E. Error Checking and Error Handling

• No matter how confident you are in the VI you create, youcannot predict every problem a user can encounter• Without a mechanism to check for errors, you know only that

the VI does not work properly• Error checking tells you why and where errors occur

− Automatic error handling− Manual error handling

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E. Error Checking and Error Handling – AutomaticError Handling

• LabVIEW automatically handles any known error when a VIruns by:− suspending execution,− highlighting the subVI or function where the error occurred,− and displaying the Error dialog box• Select File»VI Properties and select Execution from the

Category pull-down menu to disable automatic errorhandling for a specific VI

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E. Error Checking and Error Handling – ManualError Handling

• To disable automatic error handling for a subVI or function,wire its error out cluster to the error in cluster of anothersubVI or function or to an error out indicator• Use the LabVIEW error handling VIs,

functions, and parametersto manage errors

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E. Error Checking and Error Handling – ErrorClusters

• Use the error cluster controls and indicators to create errorinputs and outputs in subVIs• The error in and error out clusters include the following

components of information:− Status− Code− Source

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GOAL

Exercise 3-2Concept: Debugging

Use the debugging tools built into LabVIEW.

19DISCUSSION

Exercise 3-2Concept: Debugging

• If you have a VI with a broken Run arrow, what should youdo first?• After you fixed your broken Run arrow, your VI results show

unexpected data. What can you do next?

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Summary—Quiz

1. How do you disable automatic error handling?a) Enable execution highlightingb) Wire the error out cluster of a subVI to the error in

cluster of another subVIc) Place a checkmark in the Show Warnings checkbox of

the Error List dialog box

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Summary—Quiz Answer

1. How do you disable automatic error handling?a) Enable execution highlightingb) Wire the error out cluster of a subVI to the error in

cluster of another subVIc) Place a checkmark in the Show Warnings checkbox of

the Error List dialog box

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Summary—Quiz

2. Which of the following are the contents of the error cluster?a) Status: Booleanb) Error: Stringc) Code: 32-bit integerd) Source: String

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Summary—Quiz Answer

2. Which of the following are the contents of the error cluster?a) Status: Booleanb) Error: Stringc) Code: 32-bit integerd) Source: String

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