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Programmable safety systems and safety network systems not only provide advantages in terms of flexibility and ease of installation, but also present new techniques for achieving machine safety. A good example of new safety system concepts is demonstrated by an installation at the Warwick Manufacturing Group, University of Warwick. The FACT (Future Automation Control Technology) cell is developed as a test environment for new automation techniques. The cell is controlled with programmable logic controllers (PLCs), which have network connections to Ethernet, ControlNet and DeviceNet. These three networks are used primarily for programming, peer-to-peer communication between PLCs, and data links to and from hardware, respectively. The cell contains three robots and a conveyor system, on which a tooling pallet assembly is mounted. The area has an integrated safety system consisting of a Pilz safety controller (a PSS 3000 controller with SafetyBus, subsequently referred to as PSS), networked to 11 Pilz DI808 input/output (I/O) nodes.

If you thought the arguments over plant floor communications were resolved by the ratification of an international fieldbus standard back in 2000, think again. The emergence of industrial Ethernet as the future physical and transport medium of choice puts the whole issue back in the melting pot. Today there is widespread recognition of Profibus as the clear leader for factory automation applications in Europe, but less widely appreciated is the fact that Interbus runs a surprisingly close second, that DeviceNet rides the manufacturing roost in North America, that Modbus, without the benefit of inclusion in either or any IEC standard, is still the protocol of choice for a large proportion of industrial automation applications or that, in Asia, CC-Link, hardly mentioned in Europe or North America, leads the field, again without benefit of an IEC accolade. Move the spotlight to the process automation sector and, if anything, the picture becomes even more confused. True, there are only two serious contenders: Profibus and Foundation Fieldbus (FF), but they can't even agree between themselves what actually constitutes a process application.