I would like to ask what are the possibilities of recovering historical data from devices with which Ignition communicates remotely.
I am referring to the example of photovoltaic farms. There are devices there that operate on different communication protocols. Access to these devices is remote. Sometimes the connection to these devices is temporarily lost for various reasons (network operator, SIM failure).
When communication is lost, information about the operating parameters of the power plant is lost. This causes problems with the settlement of KPIs for this period and adversely affects summary indicators.
The idea is to cache information for the time of loss of communication and recover it when communication returns. We have devices such as PLCs available on site.
We cannot install an ignition edge instance on all sites so we are looking for any other ideas and suggestions.
If you have a modern PLC with structured memory, it is relatively easy to code a ring buffer (array of structures) to buffer your data. Each element would include a timestamp (easy to get that in 64-bits with Logix) for Ignition to use to backfill your history after comms are restored.
The only downside to this approach is that it isn’t practical to turn on and off–you would use it all the time to record history. It would simply keep up under normal conditions. This approach works best with wide tables and a scripted handshake.
The technique is generic, and should work regardless of OPC Server used. It doesn't depend on any particular OPC features. It does require custom code in the PLC to advance the ring buffer as Ignition consumes from it. This topic adds a bit more detail: