SERCOS News - Issue 1 - 2008

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2 Editorial The Real-Time Ethernet Magazine Real-time Ethernet: Speed is not everything! Ethernet is generally recognized to be a powerful and future-proof bus system which is particularly notable for its low cost and standardized physical design. Hence it always sounds highly promising, at least at first, whenever new types of bus system are based on Ethernet. At second glance, however, this image becomes somewhat clouded, not so much because of the technology or the possibilities offered by Ethernet but more because of the number of incompatible solutions competing with each in the market. The latest development is that solutions are now already being offered on the basis of Gigabit Ethernet. It should come as no surprise that the subject has become an issue for those companies and users’ organizations in particular which experience performance disadvantages because of the respective transmission method used. What is not mentioned here is that certain disadvantages have to be taken into account if Gigabit Ethernet is used, such as more complex cabling, for example, and higher costs and CPU loads for software-based solutions. Thanks to its highly efficient protocol, SERCOS III is already able to meet the performance requirements of all applications today, meaning that there is no need to switch to Gigabit Ethernet. Instead it enables concepts to be implemented which offer genuine added value for machine manufacturers. In particular this means manufacturerindependence and worldwide acceptance, as reflected in the standardized device profiles and the CIP Safety on SERCOS safety concept. We hope you have an enjoyable read. Peter Lutz, General Manager SERCOS International e.V. Küblerstraße 1, D-73079 Süßen Phone: +49 (0) 7162/9468-65 Fax: +49 (0) 7162/9468-66 e-mail: p.lutz@sercos.de www.sercos.de Quick-Info 1-0801 A1 a company SERCOS III Hardware for master and slave Driver software for master and slave Controls and IO systems Starterkits Design - Consulting - Training AUTOMATA GmbH & Co. KG · info@automata.de · www.automataweb.com Tel. + 49 (0) 82 33 / 79 16 - 0 · FAX + 49 (0) 82 33 / 79 16 - 19
The Real-Time Ethernet Magazine Sercos-Inside 3 Safe and fit for the future Many companies have several networks running in parallel, making it impossible or unprofitable to communicate with each other. This makes cooperation more difficult and results in functional losses. Yet it would be helpful if a die-casting machine was able to report a fault, not just to the staff on site, but also to the production planning systems, material management as well as the manufacturer. A direct connection between the PC of a developer located at headquarters and the control of an assembly line of a subsidiary factory could make updates much faster and more cost-efficient. Therefore companies are increasingly coming to use a unified protocol to transfer information from A to B. Here Ethernet and TCP/IP, the basis of the Internet and office communication, have become dominant. As factory automation has much higher requirements as to the robustness, reliability and safety of the information networks, Ethernet in the industrial environment looks somewhat different from Ethernet in the office. The most important requirement Industrial Ethernet has to meet is real-time communication, i.e. the assurance that important information will be transferred immediately or within a guaranteed time frame. This is the only way to coordinate complex processes. Common Ethernet allows a unit to block the line for all other participants for as a long as it takes to transmit its data completely. This leads to the typical "freezing" of the network, for instance when someone is sending an e-mail with a volume of several megabytes to many recipients. Two seconds of delay may not be a problem in the office, but in a machine, which has to coordinate 80 work cycles per minute, it would be disastrous. The second important feature is reliability. Heat, dust and vibration can never be prevented at a workplace. Strong magnetic fields may induce currents in cables that are insufficiently protected. And a cable failure is always possible where many parts are moving. None of these factors may be allowed to jeopardize the work capabilities, and the same applies to the safety from external access. However desirable it is to make communication easy, unauthorized access must be prevented in every case. The term of Industrial Ethernet actually covers various different practical solutions. Around a dozen solutions are offered, six of which – systems such as SERCOS III, PROFINET RT or EtherNet/IP – can be seen as the relevant market participants with enough international support and a sufficient number of clients. However, there are enormous differences in some cases. Some systems may offer real-time functions but with only limited synchronicity, which guarantees that several modules work in the same system cycle. Others are based on a close connection between the control and network functionality, which means that the user is restricted in his choice of automation systems. Others again might be open but demand rigid network planning with numerous control units which make modifications difficult and also make simple standard communication very slow. Today's field busses and Industrial Ethernet systems offer some basic functions which allow carrying out typical control tasks. As the complexity of the application increases, the requirements for the network increase as well. For instance, real-time applications that require the precise interaction of several electric drives or need fast processing of sensor data depend on a network with a guaranteed high performance. This is exactly the domain of SERCOS III. Thanks to Fast Ethernet with a throughput of 100 megabits per second and possible mini-
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SERCOS News - Issue 1 - 2008

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