Plant historians and relational databases are similar because they both collect and store data. But they were created for completely different purposes, and they behave differently.
The historian captures and stores data about the plant operations for the purpose of measuring plant activity. Those measurements are then used to improve plant operations or report data to regulatory bodies. The relational database collects business data for use in running the company, not just the plant. The relational database is great at answering the question: What customer ordered the largest shipment? The historian, on the other hand, is better at answering the question: What was today’s hourly unit production standard deviation? Ultimately, to make the best use of plant data, companies are finding that it helps to use both the historian and a relational database.
In manufacturing, the historian is a well-accepted tool and typically is preferred over the relational database by plant operators. “One of the reasons we chose to use the historian to track plant operations is because the database can’t keep up with the plant processes,” says Jack Wilkins, senior manager for Proficy Software at GE Fanuc Automation, in Charlottesville, Va. “Plus, the historian has a long history on the manufacturing side. It’s accepted. It’s a known quantity, like the black box flight recorder on an airliner.”
Wilkins notes, however, that the historian has limitations in its ability to analyze data effectively. “We’re beginning to see a greater need to put data in context, and the historian has little ability for context.” GE Fanuc solves this limitation in the historian by bringing in a Microsoft SQL database component.
Over at Lighthammer Software Development Corp., in Exton, Pa., Chief Technology Officer and co-founder Rick Bullotta also sees the need to work with both the historian and a relational database. “Historians do a crummy job with transaction material or genealogy, but they’re great for streaming data.” He notes that databases do poorly in the application space.
Like GE Fanuc, Lighthammer took the approach of bringing the two together, says Bullotta. “We link the historian in the plant tracking or maintenance system to a relational database, and those two different systems appear as a unified system.”