3 years ago

Automation Technologies 1/2016

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Automation Technologies 1/2016


INDUSTRIAL COMMUNICATION Unifying ethernet and process automation In factory automation, Ethernet is the basis of fast IP communication. However, the world of process automation still works with two-wire cables and 4-20 mA. But a concept study by ‘Pepperl+Fuchs’ demonstrates, that continuous data flow via Ethernet is actually possible in process automation as well. the fieldbus standard that is used, which fulfills an important prerequisite for continuous communication in the process industry. Ethernet for process automation An interview with Michael Kessler, Executive Vice President Components & Technology and Lutz Liebers, Head of the Division Process Automation at Pepperl+Fuchs Why do we need Ethernet for the process industries? E thernet, the standard form of communication technology for the constant flow of data, is nowadays almost as common as running water and power connections. Ethernet protocols are standardized worldwide and supported by virtually every automation system. Until now, due to a number of reasons, it has not been possible to use this widespread technology at the field level in process industries. To extend continuous communication via Ethernet down to the field level, a group of well-known companies from all over the world has joined under the name “Advanced Physical Layer (APL)”. Its goal is to develop common standards and basic concepts for Ethernet for applications in process automation. As a member of this group, Pepperl+Fuchs has presented its own concept study, and developed a demonstrator based on this study. Ethernet and process automation can be unified, and the technical requirements of the plant operators can be fulfilled. The demonstrator can achieve a transfer rate of up to 10 Mbit/s, and the standard fieldbus two-wire cable that is used can cover a distance of up to 1,200 meters. The Ethernet connection for the field devices is intrinsically safe. The data transfer supports all IP protocols, regardless of Michael Kessler: For a number of reasons. Future system architectures, as they are being discussed in the context of Industry 4.0, require seamless, direct communication through all levels of an automation system. Ethernet is perfect for this. At the moment, if this communication takes place at all, this is only via network transitions, which always create a bottleneck that requires laborious configuration. The requirements for the bandwidth for the data transfer are also increasing. Processes are becoming faster and the volumes of data transmitted during the configuration of the devices continue to increase. Why has Ethernet not been expanded so far? Lutz Liebers: The process industries have good reasons for working with two-wire cables. The power consumption of conventional Ethernet is far too high for the requirements in the field, and especially in hazardous areas. In addition, there are increased demands on the robustness of the connectors to ensure signal transfer over the entire lifecycle of a process plant – not to AUTOMATION TECHNOLOGIES 1/2016

mention plants in the far North or on the Persian Gulf. And the maximum length of a standard Ethernet cable of 100 meters is much too short for a refinery or a large-scale chemical plant. Can these physical barriers be overcome? Lutz Liebers: Yes, that is perfectly possible if you work on the physics of the signal transfer. Using our demonstrator, we can show the potential practical implementation. What are the special features of this demonstrator? Michael Kessler: We have intensively studied different modulation methods, and have chosen one that is ideally suited to use in process automation. It requires very low power, so it meets the requirements for a simple implementation that is intrinsically safe. The modulation method allows us to achieve a high data rate over a long cable length, without having to compromise on noise immunity. The implementation is so efficient and compact that it can be economically integrated into a simple head mounted temperature transmitter. A two-wire cable can supply up to 60 field devices and the corresponding switches with power, and allow them to communicate. The entire architecture is based on switches, which ensures compatibility with all commonly used Ethernet protocols. One feature that stands out is the migration from today’s digital fieldbus solutions. The switch installed in the field automatically detects when a ProfiBus PA or FF device is connected instead of an Ethernet field device. The switch then adapts the bound rate and protocol at the corresponding port, and converts the data to Ethernet. “The demonstrator portrays in small scale the typical communication architecture of a process plant with Ethernet signal transfer and shows that Ethernet can fulfill the requirements of the processing industry in the field.” Michael Kessler, Executive Vice President Components & Technology “Ethernet for process automation bridges the gap to Sensorik 4.0 (sensor technology 4.0), which we see as an essential foundation for Industry 4.0.” Lutz Liebers, Head of the Division Process Automation


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