SEP-OCT 2017

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has type definition has component has component AUTOMATION BASICS 42 INTECH SEPTEMBER/OCTOBER 2017 WWW.ISA.ORG sophisticated than an EtherNet/IP, Modbus TCP, or Profinet IO server. An OPC UA server models data, in- formation, processes, and systems as objects and presents those objects to clients in ways that are useful to vastly different types of client applications. It provides sophisticated services that the client can use, including: n Discovery services: Services that clients can use to know what ob- jects are available and link to other objects, data types, and metadata used to or ganize, classify, and de- scribe objects and values. n Subscription services: Services that the clients can use to identify what kind of data is available for notifica- tions. Services that clients can use to decide how little, how much, and when they wish to be notified about changes, not only to data values but to the metadata and structure of ob- jects. n Query services: Services that deliver bulk data to a client, like historical data for a data value. n Node services: Services that clients can use to create, delete, and modify the structure of the data maintained by the server. n Method services: Services that the clients can use to make function calls associated with objects. An OPC UA server is a data engine that gathers information and presents it in ways that are useful to various types of OPC UA client devices. De- vices could be located on the factory floor like a human-machine interface, or could be a proprietary control program like a recipe manager. They could also be a database, dashboard, or sophisticated analytics program lo- cated on an enterprise server. Even more interestingly, this data is not necessarily limited to a single phys- ical node. Objects can reference other objects, data variables, data types, and more that exist in nodes someplace else in the subnet, architecture, or the Internet. OPC UA organizes processes, sys- tems, data, and information in a way that is absolutely unique to the expe - than anything most of us have ever thought about before. It starts with an object that could be as simple as a single piece of data or as sophisticated as a process, a sys - tem, or an entire plant. It might be a combination of data values, metadata, and relationships. For example, a dual- loop controller object relates variables for the set points and actual values for each loop. Those variables reference other variables that contain metadata like the temperature units, high and low set points, and text descriptions. The object might also make available subscriptions to get notifications on changes to the data values or the meta - data for that data value. A client access- ing that one object can get as little data as it wants (single data value) or an extremely rich set of information that describes that controller and its opera - tion in detail. OPC UA is, like its factory floor cous- ins, composed of a client and a server. The client device requests information; the server device provides it. But, as we see from the loop controller example, what the UA server does is much more UA is a communication technol- ogy built specifically to live in that "no man's land" where data must traverse firewalls, specialized platforms, and se - curity barriers to arrive at a place where it can be turned into information. UA connects databases, analytic tools, en - terprise resource planning, and other enterprise systems with real-world data from low-end controllers, sensors, actuators, and monitoring devices. UA uses scalable platforms, multiple security models, multiple transport layers, and a sophisticated informa- tion model to allow the smallest dedi- cated controller to freely interact with complex, high-end server applica- tions. UA can communicate anything from simple downtime status to mas- sive amounts of highly complex plant- wide information. Different from plant floor systems OPC UA is about reliably, securely, and most of all, easily modeling "objects" and making those objects available around the plant floor, to enterprise ap- plications, and throughout the corpora- tion. The scope of UA is much broader Object "root" Object ViewsFolder Object ObjsFolder Object TypesFolder Object CuringOven Object Timer Object Heater Object Conveyer Method CleanCycle Object HeatElement Object HeatSensor Variable type OvenTemp Variable State Variable OvenTemp Variable MaxTemp Organizes has component has type definition Organizes Organizes has component Organizes has type definition has component has component has component has component has component has component has property Object type CuringOven Figure 2. OPC UA information model

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