Very interesting. Can you please share more details on this?.
- RTU protocol?. (Modbus or DNP3 or MQTT etc)
- Which OPC server?.
- Does the OPC server poll each RTU periodically or is it a MODBUS slave?.
- How do you download the remote datalogs from each RTU and merge it with the Ignition historian?.
If you like, you can explain the architecture in detail. May be we can work together when the opportunity comes up 
. Thanks.