Request Value Change Notifications VI

LabVIEW 2017 Datalogging and Supervisory Control Module Help

Edition Date: March 2017

Part Number: 371618K-01

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Owning Palette: Shared Variables VIs

Requires: DSC Module

Subscribes to the specified shared variables and begins generating notifications. Call this VI multiple times to add to the list of shared variables being monitored for value changes.


request changes specifies the types of value changes that this VI requests.

0all changes (default)—Requests all changes of the shared variables, including value changes, quality changes, timestamp changes, and error status changes.
1value changes only—Requests only the value changes of the shared variables.
notification refnum is a user event refnum created by the Enable Value Change Notifications VI.
shared variables is the list of shared variables for which you want value change notifications.
updates to buffer (no buffer) specifies how many value changes LabVIEW buffers for the specified shared variables. If you do not provide a buffer, LabVIEW generates notifications only for the most recent value of the shared variable. Some intermediate values of shared variables that change rapidly might not generate notifications. Only request a buffer if this VI needs to monitor every value change of a shared variable because buffering can reduce performance. This buffer only controls the behavior of the client application. You must configure buffering on the server with the shared variable.
error in describes error conditions that occur before this node runs. This input provides standard error in functionality.
shared variable value change notification returns the strictly typed user event refnum.
shared variables out returns a copy of the shared variables input.
error out contains error information. This output provides standard error out functionality.


Refer to the Simple Shared Variable and Event Monitor.lvproj in the labview\examples\lvdsc\Shared Variable Management\Simple Shared Variable and Event Monitor directory for an example of using the Request Value Change Notifications VI.


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