Data acquisition redundancy

The RedundantDIObject monitors and controls the redundant DIObject data sources at the object level. Unlike redundant AppEngines, individual DIObject data sources do not have redundancy-related states. For all practical purposes, they function as standalone objects.

Only one DIObject data source provides field device data through the RedundantDIObject at a time. Both data sources must have commonly-configured DAGroups. These must be reflected in and channeled through the RedundantDIObject, which monitors the two DIObject data sources. It also determines which one is Active at any given time. Both data sources must also have the same item address space.

After deployment or engine failover, attributes may appear to remain in an initializing state when scripting is used to activate the attributes. The script may capture the attributes while still initializing, before the engines are able to synchronize with each other. When synchronization occurs, the attributes will move to active state, but unless there is retry logic in the script, that information may not be returned. This situation can be avoided by ensuring that your scripts contain retry logic to capture the updated state of the attributes.