OPC UA in a Nutshell
OPC Unified Architecture (OPC UA) is the new standard for data communication in process automation and beyond, provided by the OPC Foundation. It is expected that OPC UA will replace the very successful Microsoft-DCOM-based specifications of the OPC Foundation (DA, HDA, and A&E) over the next few years as OPC UA unifies all the functions provided by those specifications. Because of its platform-independence and use of state-of-the-art Web service technology (see Chap. 6) it is expected that OPC UA will be applied in an even wider range of industries and applications, compared to Classic OPC. It can be deployed on devices, DCS, MES and ERP systems. The small set of easy-to-use services (see Chap. 5) allows accessing the unified address space in a reliable and secure manner (see Chap. 7). By using binary encoding on the wire OPC UA is a high-performance solution, significantly faster than XML data exchange (see Chap. 13).
OPC UA not only addresses data communication but also information modeling (see Chap. 2). With its rich address space model, it allows high-value metadata exposure and thus provides significantly more information than before. For this purpose, OPC UA uses object-oriented concepts and allows a full-meshed network of nodes related by multiple types of references. There is a high interest in these capabilities in many domains and there are already projects to standardize information models based on OPC UA. Examples of such activities are FDI where a common field device description is targeted and common activities with PLCopen (Industrial Control), MIMOSA (Maintenance Information – ERP and above), and S95 (Production Information – MES) (see Chap. 4).
With its profiles (see Chap. 12) OPC UA scales well from small servers to highly sophisticated systems. Small servers only providing simple functionality are able to run on limited hardware, exposing only a small set of simple data. Highly sophisticated servers are able to expose a large amount of complex information and to support complex functionality like querying the address space (see Chap. 9).
Nevertheless, some people are complaining that “Everything is so complicated” in OPC UA. Therefore, in the next section we will take a look at this objection against OPC UA. Finally, there is an outlook examining how OPC UA may be applied in the market and what is missing in it, to improve it even further.
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Notes
- 1.
The OPC DA specification does not use a pure object-oriented design but supports bulk operations instead of simple methods and thus the numbers are comparable.
- 2.
There are some minor exceptions from that rule. For example, the Read service and the subscription mechanisms both provide access to actual data. However, the use cases are very different and thus the simple Read only reading a value once and the subscription requiring some setup first and then getting changes of the value are both supported.
- 3.
Security has to be implemented in certified OPC UA products (see Chaps. 7 and 12). Whether security is enabled in a concrete installation depends on the configuration based on the security requirements of the installation.
- 4.
Other then XML without an XML-Schema.
- 5.
And of course a client also has to send data to the server in a format the server expects.
- 6.
The OPC UA meta model is tailored to the broad domain of exchanging real-time related data, including events and history, but not to a concrete domain like drilling or pulp and paper.
- 7.
Actually one per specification.
- 8.
This is a general statement true for all SDKs in all domains. The comfort and quality of an SDK always increases from very early versions (1.0 or even less) to higher and more stable versions.
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Mahnke, W., Leitner, SH., Damm, M. (2009). Conclusion and Outlook. In: OPC Unified Architecture. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-540-68899-0_14
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