OPC UA in EULYNX

Opportunities, Challenges, and Practical Experiences

With the increasing spread of EULYNX, OPC UA is also gaining importance as a standardized interface for diagnostic and condition data. But how can the requirements of the specification be implemented in practice, and what challenges arise when integrating into existing systems? In this article, we show the role of OPC UA in the EULYNX environment and share our own experiences regarding implementation.

Why is OPC UA gaining importance in the railway industry? 

EULYNX is a European initiative of infrastructure operators that standardizes open, manufacturer-neutral interfaces between interlockings and field elements (e.g., switches, signals, axle counters). The goal is interoperability and modularity to make components easier to exchange, reduce costs and complexity over the lifecycle, and accelerate innovation.

OPC stands for "Open Platform Communications" and is a communication standard for Industry 4.0 and IoT. Through OPC, access to machines, devices, and other systems in the industrial environment is standardized, enabling manufacturer-independent data exchange. The extension UA "Unified Architecture" refers to the latest specification of the standard. More information on OPC UA can be found in our blog post OPC UA Server on an ARM Microcontroller Using Various RTOS 

EULYNX specifies that control devices of field elements (Object Controller, OC) must transmit their diagnostic and condition data to the Maintenance and Data Management Subsystem (MDM). For this purpose, EULYNX specifies the Standard Diagnostic Interface (SDI), which uses OPC UA for provision/transmission.

OPC UA Information Models in the Context of EULYNX

Starting from EULYNX Baseline 4 Release 3, the diagnostic information to be provided via SDI is defined by an OPC UA information model. The use of information models allows for a semantically unambiguous description of the data. These are well suited for the standardized object and telegram definitions of EULYNX. In addition to the standardized and transparent structuring of the data, OPC UA information models also enable a uniform integration into higher-level diagnostic systems for further processing.

EULYNX specifies the following information models:

• SDI-XX Information Model
  Diagnostic information that must/should be transmitted by all field elements regardless of type. This includes, for example, the status of the CPU (cpuHealthStatus) or the serial number of the device (serialNumber).

• SDI-P/-LS/-IO/-TDS/-LC Information Models
  Diagnostic information that must/should be transmitted by field elements of the respective type (switch, light signal, etc.) in addition to the generic diagnostic information. This includes, for example, the current position of the controlled switch (position) or the displayed light symbol (signalVectorCurrent).

In addition to the specifications themselves, EULYNX also publishes the OPC UA models as XML Nodeset. These are intended to assist suppliers in developing EULYNX-compliant field elements.

Opportunities and Challenges in Implementing OPC UA in the EULYNX Context

EULYNX aims to standardize interfaces without unnecessarily restricting potential manufacturers regarding system architecture/used hardware. For this reason, the information model specified by EULYNX also includes optional data points and allows for design flexibility on various topics. Based on our project experience, this leads to the following opportunities and challenges: 

• This flexibility makes it possible for various system/hardware platforms to meet the requirements of EULYNX regarding diagnostic information. On the other hand, this results in the effective implementation of the specific information models by different manufacturers potentially varying. This aspect must be considered by both manufacturers and railways during development and/or integration and increases the effort/complexity of the system in favor of interoperability. 

• EULYNX and thus the SDI specification will continue to evolve with upcoming baselines. In addition to the resulting advantage of an improved specification, this may potentially lead to changes in information models, test cases, or even interfaces themselves. How to handle various baselines and releases in the field in the long term and whether/how to migrate to newer releases must be clearly defined. 

• Another aspect is the resource requirements regarding storage and performance of the implementation. This can be significant depending on the resulting data model and chosen OPC UA implementation. This can pose a challenge depending on the intended embedded hardware. In the context of a proof-of-concept with SBB, we were able to realize an SDI implementation on existing embedded hardware platforms and thereby demonstrate feasibility. More information about our PoC and the field elements can be found here: Reference Report SBB - EULYNX Field Element 

Conclusion

OPC UA has established itself within EULYNX as a central technology for the standardized transmission of diagnostic and condition data. The defined information models create the foundation for interoperability, manufacturer independence, and a long-term sustainable system architecture. However, the extensive models also lead to increased modeling, validation, and testing effort and generally higher requirements regarding the provided diagnostic information.

For successful and efficient implementation, a clean specification of the information model tailored to the deployed/to be developed system and the external systems to be controlled, as well as EULYNX and OPC UA expertise, is essential.

In various projects, we have gained experience in all phases of the V-model and are happy to support you with our acquired EULYNX and OPC UA expertise in your next endeavor.