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MAY-JUN 2019

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lining the specific interfaces the hard- ware and software components will use. These components will be used to architect, build, and start up automa- tion systems for end users. The vision for the OPAS Standard is to allow the interfaces to be used in an un- limited number of architectures, there- by enabling each process automation system to be "fit for purpose" to meet specific objectives. The standard will not define a system architecture, but it will use examples to illustrate how the com- ponent-level interfaces are intended to be used. System architectures (figure 2) contain the following elements: Distributed control node (DCN): A DCN is expected to be a microproces- sor-based controller, I/O, or gateway device that can handle inputs and out- puts and computing functions. A key feature of O-PAS is that hardware and control software are decoupled. So, the exact function of any single DCN is up to the system architect. A DCN consists of hardware and some system software that enables the DCN to communicate on the O-PAS network, called the OCF, and also allows it to run control software. Distributed control platform (DCP): A DCP is the hardware and standard soft- ware interfaces required in all DCNs. The standard software interfaces are a common platform on top of which control software programs run. This provides the physical infrastructure and interchangeability capability so end users can control software and hard- ware from multiple suppliers. Distributed control framework (DCF): A DCF is the standard set of software in- terfaces that provides an environment for executing applications, such as con- trol software. The DCF is a layer on top of the DCP that provides applications with a consistent set of O-PAS related func- tions no matter which DCN they run in. This is important for creating an efficient marketplace for O-PAS applications. OPAS connectivity framework (OCF): The OCF is a royalty-free, secure, and interoperable communication frame- work specification. In O-PAS Version 1, the OCF uses OPC UA. Advanced computing platform (ACP): An ACP is a computing platform that implements DCN functionality but has scalable computing resources (mem- ory, disk, CPU cores) to handle appli- cations or services that require more resources than are typically available on a small profile DCP. ACPs may also be used for applications that cannot be easily or efficiently distributed. ACPs are envisioned to be installed within on-premise servers or clouds. Within the OPAS Standard, DCNs represent a fundamental computing building block (figure 3). They may be hardware or virtual (when virtual they are shown as a DCF as in figure 2), big or small, with no I/O or various amounts. At the moment, allowable I/O density per DCN is not settled, so some standardiza- tion in conjunction with the market may drive the final configuration. DCNs also act as a gateway to other networks or systems, such as legacy systems, wireless gateways, digital field networks, I/O, and controllers like DCS or PLC systems. Industrial In - ternet of Things (IIoT) devices can also be accessed via any of these systems. COVER STORY INTECH MAY/JUNE 2019 13 Figure 2. OPAS establishes a system architecture organizing process automation elements into interoperable groupings. Advanced computing platform DCF DCF DCF On-premise OT data center (executing IEC 62264 Level 2 and 3 functions) DCN = DCP + DCFs Enterprise IT data centers (executing IEC 62264 Level 4 functions) Business platform Transactional computing platform Non-O-PAS environments DCF DCF Connectivity framework (OCF) Business platform communicates through apps running in a DCF, not directly to the OCF DCN DCN External OT data center (executing IEC 62264 Level 2 and 3 functions) External data centers may run DCFs that are connected to the OCF through a firewall. Stand-alone DCF environments may be used for functions such as offline engineering and simulation. Legend Non-O-PAS conformant platform DCN DCN DCN DCN DCN DCN DCN DCN DCN DCN DCS DCF DCF DCF DCS PLC Analyzer PLC Analyzer O-PAS component Machinery monitoring Field networks Safety systems Electrical systems AI/AO/DI/DO twisted pair, etc. Distributed control nodes (Executing IEC 62264 Level 1, 2 & 3 Functions

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