CLAD Debugging & Troubleshooting Techniques 5 — Questions and Answers
Question 1: What does the 'Clean Up Diagram' feature in LabVIEW do, and why should it be used cautiously during debugging?
- It removes all probes and breakpoints from the diagram
- It auto-reroutes wires and repositions nodes, which can obscure the original logical layout you were tracing (Correct answer)
- It resets all shift registers to their initialized values
- It converts all local variables to wire connections
Correct answer: It auto-reroutes wires and repositions nodes, which can obscure the original logical layout you were tracing
Clean Up Diagram rearranges nodes and wires algorithmically, which can destroy a carefully arranged layout that was helping you trace data flow during debugging.
Question 2: In LabVIEW, which VI property can you check to determine if a subVI is currently loaded in memory and could be causing stale data issues?
- VI Properties > Execution > Allow Debugging
- VI Properties > General > In Memory (Correct answer)
- VI Properties > Security > Locked
- VI Properties > Documentation > Revision History
Correct answer: VI Properties > General > In Memory
The 'In Memory' status in VI Properties > General shows whether a VI is currently loaded, which helps identify if an old compiled version is cached and causing unexpected behavior.
Question 3: You notice a LabVIEW timing loop drifts over time. Which debugging tool would best reveal if the loop body is taking longer than the intended period?
- Profile Performance and Memory tool (Correct answer)
- Execution Highlighting
- Error List window
- Breakpoint on the Wait Until Next ms Multiple function
Correct answer: Profile Performance and Memory tool
The Profile Performance and Memory tool measures actual execution time per node and loop iteration, directly showing if the loop body exceeds its timing budget.
Question 4: What is a 'stale subVI' problem in LabVIEW, and what is the correct fix?
- A subVI whose front panel is open while debugging; close the front panel to fix it
- A subVI on disk that has been edited but whose calling VIs are still using the old compiled image; fix by saving all and reloading (Correct answer)
- A subVI that has not been called in the current session; fix by calling it once
- A subVI with no connector pane wired; fix by adding terminal connections
Correct answer: A subVI on disk that has been edited but whose calling VIs are still using the old compiled image; fix by saving all and reloading
A stale subVI occurs when the source VI file is modified on disk but callers still have the old compiled version loaded; saving all VIs and doing a Mass Compile resolves this.
Question 5: Which LabVIEW error code range typically indicates hardware or driver-level errors such as DAQmx communication failures?
- Error codes 0 to 99
- Error codes -200000 to -299999 (Correct answer)
- Error codes 1 to 999
- Error codes 5000 to 9999
Correct answer: Error codes -200000 to -299999
DAQmx and NI hardware driver errors typically fall in the -200000 to -299999 range, which you can look up in NI's error code database or the Explain Error dialog.
Question 6: When a LabVIEW VI behaves differently on a target machine compared to the development machine, which of the following should you check FIRST?
- Whether the target has the same LabVIEW Run-Time Engine version as the development machine (Correct answer)
- Whether the VI's front panel color scheme matches on both machines
- Whether the development machine has more RAM
- Whether the VI's icon label is identical on both machines
Correct answer: Whether the target has the same LabVIEW Run-Time Engine version as the development machine
A version mismatch between the LabVIEW Run-Time Engine on the target and the LabVIEW version used to build the executable is a common cause of behavior differences.
Question 7: What is the function of the 'Highlight Execution' combined with 'Step Over' in LabVIEW debugging?
- Runs the entire VI without pausing, ignoring all breakpoints
- Executes a node (including any subVI it calls) as a single step without stepping into the subVI's diagram (Correct answer)
- Jumps to the next breakpoint regardless of node boundaries
- Disables all probes temporarily
Correct answer: Executes a node (including any subVI it calls) as a single step without stepping into the subVI's diagram
Step Over executes the current node — including any subVI — as one atomic step, so you can skip into the details of a subVI and move to the next node on the calling diagram.
CLAD Debugging & Troubleshooting Techniques 5
What does the 'Clean Up Diagram' feature in LabVIEW do, and why should it be used cautiously during debugging?