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Ethernet-based real-time control data bus

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Laqua,  H.
W7-X: Construction, Max Planck Institute for Plasma Physics, Max Planck Society;
W7-AS, Max Planck Institute for Plasma Physics, Max Planck Society;
Experimental Plasma Physics 3 (E3), Max Planck Institute for Plasma Physics, Max Planck Society;

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Niedermeyer,  H.
W7-X: Construction, Max Planck Institute for Plasma Physics, Max Planck Society;

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Willmann,  I.
Max Planck Institute for Plasma Physics, Max Planck Society;

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Citation

Laqua, H., Niedermeyer, H., & Willmann, I. (2002). Ethernet-based real-time control data bus. IEEE Transactions on Nuclear Science, 49(2), 478-482.


Cite as: http://hdl.handle.net/11858/00-001M-0000-0027-4140-3
Abstract
Wendelstein 7-X is designed as a steady-state experiment to demonstrate the fusion reactor relevance of the advanced stellarator concept. The experiment's control and data acquisition will be performed by a distributed system of computers and programmable logic controllers (PLCs). Data of several systems have to be combined flexibly to control the machine, requiring a data exchange on a millisecond time scale between several connected units. A discharge can last up to half an hour, thus, the connections may vary during a discharge. Hence, it is desired to provide control relevant data, e.g., measurands, set points, interlock signals, cyclically via a bus system. The paper will analyze the special quality of control data streams and deduce the basic requirements for a real-time data bus. Ethernet is a candidate for the data bus since it is a widely used broad-band bus with a foreseeable potential for development. Because of its nondeterministic arbitration algorithm Ethernet is generally considered not to be suited for hard real-time applications. It is possible to circumvent this disadvantage of Ethernet either by using switching techniques or a software token to obtain a reliable base for hard real-time data transport.