Types of Refnum Controls and Indicators

LabVIEW includes the following refnum controls:

Byte Stream File RefNum—Used with text or binary byte stream files. Use this type of refnum when you open or create a file in one VI but want to perform I/O operations on the file in another VI. You must have a refnum control on the front panel of the VI that performs I/O operations and a refnum indicator on the front panel of the VI that opens or creates the file.
Data Log File RefNum—Used with datalog files. Because datalog files have an inherent structure, the Data Log File Refnum passes the refnum and a description of the file type to and from calling VIs. Place a control inside the refnum to define the structure of the file. For a file that contains numbers, create a datalog refnum that contains a number. If each record in the file contains a pair of numbers, place a cluster inside the refnum and place two numeric controls inside the cluster.
VISA Session RefNum—A unique logical identifier used with the VISA VIs and functions to communicate with a resource. The VISA session is maintained by the VISA resource name control and is not seen by the user.
IVI RefNum—Used with the IVI VIs.
IMAQ Session RefNum—Used with the Image Acquisition VIs.
Application—Used with VI Server. Use this refnum control when you open a reference to a LabVIEW application and you want to pass the reference as a parameter to another VI. By passing this refnum to the VI Server, you can control the behavior and read properties of the application.

You can right-click an application refnum control and select Select VI Server Class from the shortcut menu to change the data type of the control—an application, a VI, a control or indicator, or a strictly-typed VI.
Control RefNum—Used with VI Server. Use this refnum control when you open a reference to a front panel control or indicator and you want to pass the reference as a parameter to another VI. By passing this refnum to the VI Server, you can control the behavior and read properties of the control.

You can right-click a control refnum control and select Select VI Server Class from the shortcut menu to specify the data type of the control—an application, a VI, a control or indicator, or a strictly-typed VI.
VI RefNum—Used with VI Server. Use this refnum control when you open a reference to a VI and you want to pass the reference as a parameter to another VI. By passing this refnum to the VI Server, you can control the behavior and read properties of the VI.

You can right-click a VI refnum control and select Select VI Server Class from the shortcut menu to specify the data type of the control—an application, a VI, a control or indicator, or a strictly-typed VI.

Strictly-typed VI refnums have data type information that includes the connector pane of the VI. You can use strictly-typed VI refnums to call a dynamically loaded VI using the Call By Reference function. Right-click the refnum control and select Select VI Server Class»Browse from the shortcut menu to select a VI from disk that has the connector pane you want. You also can drag a VI icon, connector pane, or a subVI icon from a block diagram or the Hierarchy window to a VI refnum control to specify the type of a strictly-typed VI refnum control.

Use VI refnum controls to pass a VI refnum from one VI to another. The Open VI Reference function requires a strictly-typed VI refnum control as a type-specifier input when you want a strictly-typed reference to a VI. In this case, the value of the refnum control is unimportant. The function uses only the type.
Menu RefNum—Used with the Menu functions. Use this type of refnum when you want to pass a VI menu reference to a subVI.
TCP Network Connection RefNum—Used with the TCP/IP functions. Use this type of refnum when you open a network connection in one VI but want to perform I/O operations on the network connection in another VI.
Occurrence RefNum—Used with the Occurrence functions. Use this type of refnum when you generate an occurrence in one VI but want to set or wait for the occurrence in another VI.
Automation RefNum—Used with the ActiveX Automation functions. Use this type of refnum when you open a reference to an ActiveX Server Object and you want to pass it as a parameter to another VI. To specify the type of the refnum, right-click it and select Select ActiveX Class from the shortcut menu to browse the list of available ActiveX Server applications.
Notifier RefNum—Used with the Notifier Operations functions. Use this type of refnum when you want to suspend the execution of a block diagram until you receive data from another section of the block diagram or from another VI running on the same computer. This refnum control is not located on the Controls»Refnum palette. You must right-click an input terminal of a Notifier Operations function and select Create Control from the shortcut menu to create this refnum control.
Queue RefNum—Used with the Queue Operations functions. Use this type of refnum when you want to store data in a queue, which you can later retrieve as individual elements or as an array of all the data elements. This refnum control is not located on the Controls»Refnum palette. You must right-click an input terminal of a Queue Operations function and select Create Control from the shortcut menu to create this refnum control.
Semaphore RefNum—Used with the Semaphore VIs. Use this type of refnum when you create a semaphore in one VI but want to acquire or release the semaphore in another VI.
Rendezvous RefNum—Used with the Rendezvous VIs. Use this type of refnum when you create a rendezvous in one VI but want to wait at the rendezvous in another VI.
Config Data RefNum—Used with the Configuration File VIs. Use this type of refnum when you open a configuration file in one VI but want to read from it or write to it in another VI.