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When you enable alarming for a shared variable and deploy the shared variable, LabVIEW creates shared variable alarming data items in the Shared Variable Engine (SVE). The alarming data items reside in a folder named Alarms. This Alarms folder resides under the shared variable.
You use alarming data items to read from and write values to alarms. You can read and write alarming data items by using the NI Publish-Subscribe Protocol (NI-PSP) clients, such as the Shared Variable node, VI, and functions, the NI Distributed System Manager, and so on. To launch the System Manager from LabVIEW, select Tools»Distributed System Manager.
To read from or write a value to an alarming data item, you can specify the data item URL in the following format: \\computer\process\variable\Alarms\alarm\data_item. If you use the Shared Variable Node, VI, and Functions to read and write alarming data items, specify the data item URL in the following format: ni.var.psp://computer/process/variable/Alarms/alarm/data_item. In both URL formats, variable stands for the name of the shared variable under which the data item resides and alarm stands for the alarm name you specify.
The default values of alarming data items are the values that you specify for the alarming property when you configure a shared variable. However, the values that you write to alarming data items do not change the values that you specify for the alarming property. If you restart the SVE or the computer, LabVIEW initializes the values you specify for alarming data items. The values that LabVIEW initializes are the same as the values you specify for the alarming property.
The following table lists the shared variable alarming data items that the LabVIEW Datalogging and Supervisory Control (DSC) Module supports.
|Data Item||Data Type||Access Type||Description|
|Ack||Boolean value||Read||Specifies whether an alarm is acknowledged for a shared variable.|
|AckType||32-bit unsigned integer||Read/Write||Specifies how an alarm is acknowledged.
|AlarmState||Boolean value||Read/Write||Sets alarm conditions for Boolean shared variables. You use this data item to set the Boolean shared variable to be in alarm state when the value is either TRUE or FALSE. This data item exists when you enable a Boolean alarm.|
|deadband||64-bit floating-point number||Read/Write||Specifies the alarm deadband for a shared variable as a percentage of the full scale range. This data item exists when you enable a HI_HI alarm, HI alarm, LO alarm, or LO_LO alarm.|
|Description||String||Read||Specifies the description of the alarm.|
|Enable||Boolean value||Read/Write||Specifies whether an alarm is enabled for a shared variable.|
|level||64-bit floating-point number||Read/Write||Specifies the value, in engineering units, that evokes the alarm condition. This data item exists when you enable a HI_HI alarm, HI alarm, LO alarm, or LO_LO alarm. The level values of the numeric alarms conform to the following rule: HI_HI level>HI level>LO level>LO_LO level.|
|Log||Boolean value||Read/Write||Specifies whether alarm logging is enabled.|
|Priority||32-bit unsigned integer||Read/Write||Specifies the priority of the alarm. Enter a value between 1 and 1000, where 1000 is the highest priority.|
|Set||Boolean value||Read||Specifies whether an alarm is set for a shared variable.|