OPC UA

User-friendly network

In a user-oriented and future-proof network, existing and new technologies function smoothly alongside one another as well as between cross-manufacturer solutions. A good example is the combination of OPC UA and PROFINET. With OPC UA as middleware, data and information models can become object-oriented. PROFINET with its application profiles virtually takes over the supply of the necessary information.

To ensure that this interaction works and is uniform for all PROFINET devices, the PNO established the 'OPC - PNO Working Group-' as a joint WG with the OPC Foundation. The most important task was the standardized mapping of existing and proven data and information models from PROFINET to OPC UA. The goal was to create a 'Joint OPC UA Companion Specification'. Since January 2020, version 1.0 of the specification has been officially released. This first version focuses on applications in the areas of asset management and diagnostics. The main objective was to map the different views of the different user groups.

From a technological point of view, production data or process sequences of a machine are important, but from a maintenance point of view, the equipment used is important. Energy management also requires different information, while details about the network are interesting for a different user group. The PROFINET view deals with the representation of the devices and their communication relationships, a network view deals with interfaces and ports, and a functional view deals with the information model of a control loop or sensor function, for example. These different views of the same machine or plant must fit together, which is achieved by semantic references.

Which views, i.e. which submodels and data are important for everyday operation, were developed on the basis of a detailed use-case description within the framework of the Companion Specification.

In contrast to the classic Companion Specifications based on OPC UA DI, which only deal with the modeling of a device, the PROFINET Companion Specification refers to the modeling of a complete system automated with PROFINET with a large number of controllers and devices.

Accordingly, the PROFINET model consists of the controller and the device submodel. The controller submodel contains the PROFINET connections (application relations) with modules and submodules configured in the PROFINET controller. The device submodel consists of the PROFINET devices with their actually existing modules and submodules. These two submodels are connected to each other via OPC UA references.

In addition, the information model includes the mapping of the physical network topology of the PROFINET network. Thus, the exact cabling of the PROFINET devices with their Ethernet interfaces, ports, and cables is included in the OPC UA information model and can be used for network diagnostics. The OPC UA information model uses OPC UA Amendment 7 'Interfaces and Add-Ins'. An appendix to the specification describes the use of the information model as an example.

Fail-safe communication thanks to OPC UA Safety

Modularization and interoperability are playing an increasingly important role in modern plants and are the core requirements for Industrie 4.0. PROFIBUS & PROFINET International (PI) was an early adopter of OPC UA as an open, cross-vendor standard for machine-to-machine communication. OPC UA allows cross-vendor networking between machines, regardless of the fieldbuses used within the machine.

However, up to now OPC UA has not been able to transfer fail-safe data as is the case with fieldbuses with PROFIsafe. Safety functions involving controllers from different manufacturers therefore had to be performed conventionally with direct cabling or using a special coupler.

OPC UA Part 15:

Safety now enables direct safe communication between controllers. It is a specification defined jointly by PI and the OPC Foundation. OPC UA is already the most important standard for machine-to-machine communication.

PI's many years of experience in the field of functional safe communication and PROFIsafe ensure that OPC UA Part 15: Safety meets all requirements of the IEC61784-3 standard (functional safety of fieldbuses). The safety mechanisms and many features have been adopted from PROFIsafe. In particular, OPC UA Safety also uses the proven "Black Channel" mechanism of PROFIsafe. For this purpose, OPC UA Safety implements the necessary safety measures in a safety layer above the communication layer.

The advantages of PROFIsafe - independence from synchronized clocks, an unlimited number of network terminals and network devices, as well as an unlimited communication rate - are retained.
 

However, OPC UA Safety also offers functions that were previously not possible with PROFIsafe. These include user data with any structure and a length of up to 1500 bytes, the creation of any network topology (star, line, grid, ...), hierarchical safety IDs for simplified management of series machines, and dynamic connection setup with changing partners.
 

The last feature in particular is completely new and offers previously unattainable flexibility. Until now, a static, unique code name had to be assigned for each possible safety connection. This must be known at both ends of the connection in order to check incoming telegrams to see whether they come from the correct sender. If you think, for example, of mobile robots that move independently from machine to machine, this procedure becomes complicated. As soon as only one new station is added, all machines mustbe reparameterized. This increases effort and reduces flexibility.

Particularly in the Industrie 4.0 context, it should be possible to reconfigure the safety function without human consent. In this context, the OPC UA Safety solution has the advantage that the check for the correct data source is no longer based on a code name for each connection, but that each data source is directly assigned a corresponding ID. This allows several subscribers to alternately access the same data source and the subscribers do not have to be known to the source. In the example this means that mobile robots can be added at any time without having to adapt the machines.

Outlook

The next steps are also already planned. Test specifications are currently being drawn up in which test procedures are defined. In addition, the development of a software tool for automatic testing has been commissioned. It is also necessary to establish a certification and acceptance procedure similar to PROFIsafe. This is a prerequisite for the simple and fast safety certification of products that implement OPC UA Safety. Case studies will also be created to demonstrate the new features of OPC UA Safety. These include the simplified management of safe addresses for series machines and the ability to communicate with different partners over the same connection during runtime. Furthermore, an OPC UA Mapper for Pub/Sub is specified in order to be able to implement safety functions with high demands on response time.

Convincing combination

PROFINET has been fulfilling diverse and complex tasks in the field for many years, for example, during machine startup, in engineering or for redundancy requirements. More than 30 million field devices with a PROFINET interface provide the relevant information. OPC UA complements this technology because it allows object modeling from a wide range of data sources. Thanks to this combination, the result is real added value for users, as the following practical examples from asset management and diagnostics show. The first version of the PN-OPC UA Companion Specification focuses on these two applications.

Asset Management

Many users do not know which devices with which hardware or firmware status have been installed in a system over the years. Without such information, however, maintenance plans cannot be created, let alone managed properly. This is now being solved.

The first version of the PN-OPC UA Companion Specification solves the requirements of asset management and diagnostics with the following details:

• Asset Identification

     Listing of all PROFINET Nodes (Controller and Devices) with:
          - Modules and submodules (Real and Expected)
          - I&M and Asset Information (Tag Function, Tag Location, Versions, Vendor, ...)
          - Network Parameters
          - Physical Topology of the PROFINET Network

• Detection of asset changes

          - New, Remote and Replaced Devices / Submodules - Docking Devices
          - Firmware Updates in the Devices
          - Changes in Physical Topology

• Changing Asset Information

          - Name of Station, Tag-Function

 Diagnosis

More detailed information from the field is also required for intelligent diagnostic strategies. Here too, the PN-OPC UA Companion specification provides practical strategies.

• Display PROFINET Connections (ARs)
• Recognizing the differences between the configuration in the controller and the real assets (devices, modules, submodules)
• Reporting the PROFINET device diagnoses
• Network diagnostics (counter, wrong neighbours)

OPC-Server

The corresponding OPC-Server in this illustration can be installed in different devices:

  1.      PLC

  2.      Gateway/Edge

  3.      Direct Device-Integration

Depending on the application and environment, these solutions have various advantages.