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OPC UA down to the sensor

Implementation of Industry 4.0 production requires digital consistency – from the sensors all the way up to the ERP level. All too often, a heterogeneous mix of bus systems and a lack of overarching standards make it difficult to achieve this kind of consistency. With the integration of OPC UA into POWERLINK, help is on the way.

As the tasks being solved by industrial automation grow in complexity, the trend toward decentralized control architectures continues. Having peripheral devices equipped with onboard intelligence and connected via fieldbus and industrial Ethernet allows automation solutions to be extremely flexible, modular and customizable. It is not unusual for a given machine to be composed of numerous subsystems and machine modules, each with its own controller.

Open standard

"Effective communication between the individual subsystems and components is a decisive factor in the productivity of these types of solutions," explains Stefan Schönegger, managing director of the Ethernet POWERLINK Standardization Group (EPSG). At the same time, it is very important to manufacturers of machinery and equipment that their options are not restricted by proprietary solutions. "OPC UA perfectly complements POWERLINK for communication between the field and ERP levels," says Schönegger.

OPC UA is an open standard that has been implemented by all the major control system manufacturers. It ensures that machines with controllers from different manufacturers can be easily coordinated as a single system. The protocol is also platform-independent, and the communication stack can be ported to any operating system or embedded hardware. "OPC UA is the only protocol that combines all of these benefits," says Schönegger. "For this reason, the EPSG relies on OPC UA as the communication protocol from the field level all the way up to ERP systems."

Close partnership

The OPC Foundation and the EPSG are collaborating on interface-free communication within and between production systems. At the 2015 SPS IPC Drives, the two organizations announced that they were working on the required companion specification. "With POWERLINK we've found a powerful new partner," adds Tom Burke, president and executive director of the OPC Foundation. "POWERLINK is an ideal match for OPC UA towards the machinery level and the associated real-time requirements."

"In the first stage, the machine controller will act as a gateway between the IT-related OPC UA world and the real-time world of POWERLINK," explains Schönegger. All the machine data is mapped from the OPC UA server to the machine controller, so it is provided in a standardized way. "This allows SCADA or MES systems to access sensor data, for example, without having to know anything about the inner workings of the machine."

"The companion specification takes this even one step further," says Schönegger. In the future, it will be possible to fully integrate OPC UA into the POWERLINK protocol. In its asynchronous phase – independently of the real-time data – POWERLINK is able to transmit any Ethernet protocol. "OPC UA can be completely integrated into the POWERLINK protocol with no extra effort."

OPC UA Companion Specification for POWERLINK Thomas Burke and Stefan Schoenegger EPSG
Thomas J. Burke (left), president of the OPC Foundation, and Stefan Schönegger, managing director of the EPSG, announced the development of an OPC UA companion specification for POWERLINK at the 2015 SPS IPC Drives trade fair.
OPC UA is transmitted in the asynchronous phase of the POWERLINK cycle.

No more gateways

As a result, gateways become superfluous. There is no need for an interface between the worlds of POWERLINK and IT. The machine controller doesn't even need to know OPC UA, because it only acts as an Ethernet router. A SCADA system will be able to take advantage of OPC UA to do things like access a sensor, change parameters or retrieve diagnostic information. All OPC UA services will be available without limitations.

"At the sensor/actuator level, I/O components can be used that speak both POWERLINK and OPC UA," says Schönegger. These I/O components can send the same process and parameter data to the controller via POWERLINK and to the higher-level system via OPC UA – simultaneously and independently.

Easy engineering with POWERLINK

Like OPC UA, the POWERLINK protocol is strictly software-based, with a stack that can be accessed externally and ported to all other platforms. "The combination of OPC UA and POWERLINK provides the maximum amount of freedom when engineering machines and systems," says Schönegger. Using PLCopen-compliant OPC UA function blocks makes it easy to develop applications – regardless of the control system manufacturer.

Machine #1: The machine controller receives sensor and actuator data via POWERLINK and supplies it to the higher-level system via OPC UA.
Machine #2: Through direct integration of OPC UA into POWERLINK, a SCADA system can access a sensor directly – there is no need for gateway functionality in the controller.
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