MCQ Flashcards

Where can VI be described so that the summary shows up in the pop-up box for Show Context Help?

Answer: In the VI Properties Documentation window

Text entered in the VI Properties Documentation window is what LabVIEW displays in the Context Help (Show Context Help) pop-up when you hover over the VI. A free label only appears on the front panel itself, editing the help files affects LabVIEW's manuals rather than your VI, and the Context Help window only displays information—you can't type a description into it.

Can data be sent over a wire between parallel-running loops?

Answer: No

No—LabVIEW uses dataflow, and a wire requires a source and destination that execute in sequence, but two loops running in parallel have no defined data-dependency order, so a wire between them would force them to run sequentially instead of in parallel. To pass data between parallel loops you must use mechanisms like queues, notifiers, or local/global variables instead of a direct wire.

The definition of a Tab Control is which of the following?

Answer: A type of enumerated control

A Tab Control is fundamentally an enumerated control: each page (tab) corresponds to an integer value, just like an enum, and selecting a tab returns that value. It does not output ASCII values, the tab order, or a cluster of the contained controls—those describe unrelated behaviors.

Which server needs to be started before Data Socket VIs can be used?

Answer: Data Socket server

The DataSocket server must be running before DataSocket VIs can publish or subscribe to data, since it is the component that brokers the data connections. OPC, FTP, and HTTP servers handle different protocols and are not what DataSocket VIs connect to.

A coercion act signifies:

Answer: A data buffer is created to handle data conversion

A coercion dot signifies that LabVIEW automatically inserted a data conversion at that terminal, and to do so it creates a buffer to hold the converted copy of the data—which is why coercion dots can increase memory use. It does not mean values are out of range, that types are consistent (consistent types need no coercion), or that a polymorphic operation is occurring.

Which of the subsequent cannot be used for data transfer?

Answer: Notifiers

Notifiers are a synchronization mechanism used to broadcast a message or signal to waiting code, not a means of reliably transferring a data payload (messages can be missed if no one is waiting). Local variables, queues, and semaphores can all move or guard data between parts of a program, making Notifiers the one not used for data transfer.

You have a control on a VU's front panel and need to change one of its attributes while the VU is running. Which of the following would you choose as your best course of action?

Answer: Create an implicit property node and select the property to modify

To change a property of a control on the same VI's front panel at run time, you create an implicit property node, which is already bound to that specific control and requires no reference wiring. A control reference passed to a property node works but is the explicit, more roundabout approach for the same VI; local variables and shared variables change values, not properties.