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Safety becomes the next networking battleground
Published:  01 January, 2006

Safety becomes the new networking battleground

At the recent SPS/IPC/Drives show in Germany, safety-related bus systems were a hot topic, with several demonstrations of working systems, and news of other developments.

For example, the three regional organisations that promote the Sercos technology announced an extension to the protocol that will allow safe data to be carried on Sercos for applications up to SIL3. Called Sercos safety, it is independent of the transport layer and is available for Sercos II and III and other media, although it works best with the new Ethenet-based Sercos III.

Up to 64 bits of safe data can be carried in Sercos III data telegrams and can be exchanged between slaves using peer-to-peer communications without needing a central master. A safety network can extend over several subordinate Sercos networks. The Sercos safety protocol is being evaluated by the TÜV Rheinland test house and the first products are expected to be available this year.

TÜV Rheinland has already confirmed the suitability of another safety protocol, EPLsafety which claims to be the only open, network-independent protocol for security critical applications to the SIL 3 level. Although EPLsafety is optimised for Ethernet PowerLink, it is independent of the transport protocol, and can be used with CANbus systems, TCP/IP on Ethernet, and other fieldbuses and networks.

Volker Sasse, chairman of the Ethernet PowerLink Standardisation Groups` safety work group, says that other safety bus protocols are linked closely to particular fieldbuses. "These protocols cannot be used with other buses or industrial Ethernet," he says. "With EPLsafety, we have broken away from this tradition, and offer an interoperable, open safety protocol for any network."

Another contender entering the safety arena is the Japanese-dominated CC-Link organisation which has been developing a network called CC-Link Safety since 2004, with the first products expected to go on sale this year. CC-Link Safety complies with SIL3, is compatible with standard CC-Link, and operates at speeds of up to 10Mb/s. It can use existing CC-Link cables and is designed to detect communication errors such as unexpected delays or data errors.

At the Nuremberg show, Profibus International released Profisafe V2 which can be used both on Profibus DP and Profinet I/O networks and is suitable for applications including drives, motion control and production and process automation. The safety layer is independent of the communication system, and includes the backplane buses of PLCs and field devices. TÜV has given Profisafe V2 a positive assessment, and the protocol is suitable for applications to the SIL3 level.

Finally, after more than two years of development, the PLCopen organisation released its Safe Software specification, which is integrated with logic and motion in its IEC 61131-3-based development environment. It is hailing the development as "the first functional saftey standard". PLCopen says the specification will help developers to integrate safety-related functions into their systems from the start of the development cycle.

Rexroth is implementing the PLCopen safety principles in its IndraDrive range and is offering suitable function blocks. Another company supporting the PLCopen initiative is KW Software which claims that its Safeprog programming system meets the PLCopen guidelines for safe programming user interfaces. It also plans to implement 17 PLCopen safety function blocks by mid-2006 and expects to be the first company to win a PLCopen Safety Certificate for a complete platform.

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