Managing I/O with Shared Variables (DSC Module)

You can use shared variables to represent a real-world input/output point. With the LabVIEW Datalogging and Supervisory Control (DSC) Module, you can configure how LabVIEW scales shared variable data, logs shared variable data to a historical database, and sets alarm levels and priorities for shared variable data. You also can bind shared variables to I/O servers, such as the OPC server, or to a shared variable published by another instance of LabVIEW on the network.

Note  You can use the features the DSC Module adds only for network-published shared variables.

You can configure the following shared variable properties:

• Shared variable data type
• Initialization values
• Update, logging, and alarm deadbands
• Units of measurement to data
• Alarm messages for a shared variable whose values enter the alarm ranges you set
• Data binding
• Security settings
• Scaling

LabVIEW saves shared variable information in LabVIEW project library (.lvlib) files. Shared variables communicate between VIs, remote computers, and hardware through the Shared Variable Engine (SVE). The SVE uses the NI Publish-Subscribe Protocol (NI-PSP) data transfer protocol to write and allow users to read live data.

You can include as many shared variables in a project library as you need. However, you might notice performance issues if you have insufficient system resources. Refer to the LabVIEW Datalogging and Supervisory Control Module Release and Upgrade Notes for more information about system requirements.

The DSC Module also adds OPC functionality to LabVIEW, allowing shared variables to connect to OPC servers and clients. Create an OPC Client I/O server to connect shared variables to OPC server data items manually, or use the Multiple Variable Editor window, available by right-clicking a project library or shared variable in the Project Explorer window and selecting Multiple Variable Editor from the shortcut menu. LabVIEW automatically publishes deployed shared variables to the OPC server.

Managing I/O with Tags

Tags are data sources that contain values, traces, alarms, and events of multiple shared variables and I/O server data items. You can manage the following shared variable properties programmatically by using the Tags VIs.

• Values of shared variables
• Alarms of shared variables
• Bindings between front panel objects and shared variables
• Trends of shared variables