A bus-independent safety protocol
03 June 2010
For a long time now, the automation industry has been demanding a uniform standard for safety systems because the development of safety-related technology is very cost-intensive and the investment risk is high. With openSAFETY, the Ethernet PowerLink Standardisation Group (EPSG) has now laid the foundation for the first completely open safety-related data communication protocol for all areas of automation. With communication cycles in the microsecond range, the TUV Rhineland certified protocol guarantees fast response times and suitability for use in systems rated up to SIL 4.
Because openSAFETY is bus independent, it can be used with all fieldbus or industrial Ethernet systems. At the recent Hanover Fair, EPSG successfully demonstrated four different openSAFETY configurations, which were created using popular industrial Ethernet protocols, including Sercos III, Modbus TCP, EtherNet/IP and PowerLink. On the face of it, users now have what they have been seeking - a complete, certified safety system that runs on all transport protocols.
The black channel principle
The key to interoperability with arbitrary transport protocols is openSAFETY’s ‘black channel’ principle. It doesn't matter which transport protocol is used to transport the safety frames because all safety-related mechanisms are integrated exclusively on the application layer of the protocol, and its functionality is therefore independent of the underlying transport layer. openSAFETY continually monitors all transfered data content to ensure that it is complete, that it has the correct transfer sequence and that the transfer duration is maintained. All transfer errors are recorded immediately so that industry-specific communication methods and even single-channel, non-safe transport networks can be used as the basis for communication without limitations.
The structure of the openSAFETY protocol is characterised by three things: the definition of data transport using an extremely flexible telegram format; the integrated services for configuration and automatic parameter distribution, and a communication structure that achieves optimum machine productivity using cross traffic. The crucial advantage is the reduction of safety-relevant braking distances, which allows safety margins to be ideally dimensioned and machine cycles to be increased.
The EPSG provides support for openSAFETY, offering assistance with certification and conformance testing. The protocol is available for free download as open source software from http://www.ethernet-powerlink.org/
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