OPC UA as an end-to-end communication solution right down to field level - for both production and process technology.

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More than 300 experts from more than 60 companies are currently working in the technical working groups, which are open to all members of the OPC Foundation, to develop corresponding concepts and specifications.
Work on the first version of the specification has made good progress over the past year - despite Covid-19 and the associated restrictions.

The basic concepts for the controller-to-controller (C2C) use case were largely approved and have been incorporated into the first draft specifications. A first release candidate was completed in November of last year, on the basis of which prototypes are being implemented and the draft specifications validated. At the same time, a working group is developing test specifications that will be implemented in corresponding test cases for the OPC UA certification tool (CTT).

OPC UA at field level - the system architecture

Peter Lutz is Director Field Level Communications at the OPC Foundation.

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The extensions specified by the FLC initiative are based on the OPC UA framework (IEC 62541), which enables secure and reliable, manufacturer- and platform-independent information exchange.
Controllers and field devices support the connection-oriented client/server communication model as well as the publish/subscribe extensions, which are indispensable for communication at field level due to the corresponding requirements for flexibility, efficiency and deterministics. The security mechanisms specified in OPC UA are also used, which, among other things, support authentication, signing and encryption of the data to be transported and can be used for both client/server and publish/subscribe communication relationships.

OPC UA-based system architecture with extensions for the field level.

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The initial release candidate of the FLC initiative, completed in November 2020, consists of four specification parts (OPC UA Parts 80-83) and focuses on C2C (controller-to-controller) communication for the exchange of process and configuration data using peer-to-peer connections and basic diagnostics:

- Part 80 (OPC 10000-80) provides an introduction and overview of the basic concepts of extending OPC UA for communication with and in the field level.

- Part 81 (OPC 10000-81) specifies the basic information model for controllers and field devices (Automation Components) and the communication concepts to fulfill the various use cases and requirements of factory and process automation.

- Part 82 (OPC 10000-82) describes network services such as topology detection and time synchronization.

- Part 83 (OPC 10000-83) describes the data structures for the exchange of information required for offline engineering using descriptors and descriptor packages.

Work on the safety solution for OPC UA (OPC UA Safety) is also very advanced. The first OPC UA Safety specification, which is based on client-server mechanisms and emerged from a joint working group with Profibus & Profinet International (PI), was adopted in November 2019 (Part 15, OPC 10000-15). A revision of the OPC UA Safety Specification will be available shortly, which describes the extensions for OPC UA Publish/Subscribe and the parameterization of safety participants. One of the special features of the safety concept for OPC UA is that safe participants can be dynamically integrated into the communication even while a machine or system is in operation, which is not possible in this form with conventional safety protocols.

There is also progress to report with regard to Motion. Since mid-2020, a working group has been developing an OPC UA-based drive solution.
OPC UA Motion comprises the specification of motion control functions for various types of motion devices such as controllers, standard drives, frequency converters and servo drives. The FLC Steering Committee has agreed to build on the CIP Motion and Sercos specifications and adapt them to the OPC UA information modeling and system architecture, taking into account corresponding Industry 4.0 use cases. By building on existing concepts and specifications - as with safety - the specification work can be significantly accelerated.

The combination with TSN and APL

Figure 4: Semantic interoperability with OPC UA from the sensor to the cloud.

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In principle, the OPC UA framework is transport-independent and can therefore be used flexibly with various underlying communication protocols and transmission physics.
Ethernet Time-Sensitive Networking (Ethernet TSN) and the Ethernet Advanced Physical Layer (Ethernet APL) are seen by the OPC Foundation as important components of the strategy to extend OPC UA to all use cases and requirements in factory and process automation and to implement the vision of a fully scalable, industrial interoperability solution.

The combination with TSN

An underlying Ethernet TSN enables deterministic data transmission via OPC UA, which is particularly essential for demanding automation applications. On the other hand, TSN allows different applications and protocols to be operated via standardized hardware and a common network infrastructure. This makes it possible to implement convergent industrial automation networks in which different IT and OT protocols coexist. A working group of the FLC initiative is currently working out which TSN sub-standards are mandatory for OPC UA-based end devices and infrastructure components in order to meet the defined requirements for performance, flexibility and user-friendliness. The OPC Foundation has made a clear commitment to the TSN-IA profile, which is being developed in the IEC/IEEE 60802 working group. For this reason, the OPC Foundation has entered into a liaison with the IEC SC65C and IEEE 802.1 standardization bodies.

The combination with APL

Ethernet APL describes a physical layer for Ethernet that has been specially developed for the requirements of the process industry. Ethernet APL enables high-speed data transmission over long distances, the supply of power and data via a common, twisted two-wire cable and protective measures for safe use in hazardous areas. This makes Ethernet APL the pioneer for the use of OPC UA and other Ethernet-based protocols in the process industry. Due to the particular importance of this technology, the OPC Foundation joined the Advanced Physical Layer (APL) project group in June 2020 to develop and promote APL together with other non-profit organizations and various industry partners.

The combination with 5G

The FLC initiative: The following companies are members of the steering committee of the Field Level Communications Initiative and support it both financially and with technical expertise.

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However, data exchange via OPC UA is not limited to wired or radio-based Ethernet communication. Support for the 5G mobile communications standard is also on the OPC Foundation's roadmap. The mapping to 5G will fit seamlessly into the existing OPC UA architecture, so that all protocol and profile extensions of the FLC initiative currently in specification will be usable not only via Ethernet and Ethernet TSN, but also via 5G.

The OPC UA (IEC 62541) framework with the extensions specified by the FLC initiative for the field level, in combination with subordinate communication standards such as APL, TSN and, in future, 5G, offers a complete, open , standardized and interoperable solution that not only meets the requirements for industrial communication, but also enables consistency and semantic interoperability from the field level to the cloud.

This approach - in combination with the diverse Companion specifications - ensures that data and interfaces can be standardized as far as technically possible at the data source - if feasible directly in the device: A flow meter will directly deliver standardized 'OPC UA flow measurement data' as soon as the APL cable is plugged in. Similarly, servo drives process standardized 'OPC UA drive setpoints' directly and provide actual drive values as soon as they are integrated into a machine network via Ethernet TSN.