OPC UA or OPC Unified Architecture is the latest standard for OPC communication, it eliminates the OPC use of DCOM, it integrates all the common OPC standards into one, and it has greater security features.
It came out in 2006 so why do I not see it everywhere?
I really have a hard time answering that question. I don’t know and even ten years later most Historians and DCS systems fail to have OPC UA connectivity. The process control industry as a whole tends to be slow to upgrade and adopt newer technology unless a new process facility is built and it seems that no one builds new facilities; they just “expand” them. Think of all the places you may know of that have an LCN or still use standard MODBUS for device communication.