Fulfilling temporal constraints in fieldbus

Field busses are emerging as a replacement of direct connections from control systems to the process. Many proposals such as FIP, PROFIBUS, CAN, LONWOKS have been made to solve the interconnection problem. Some, like FIP and PROFIBUS, are national standards. However, the temporal requirements, as expressed by bodies like IEC, ISA, IEEE, CENELEC, ISO TCCA, IFC or European projects in the field, are not completely fulfilled by these proposals or not even addressed. In this paper, we first detail the temporal as well as spatial requirements among which consistency plays a key role. We then explain to which extent these requirements are addressed by the different proposals. This analysis shows that none of the proposals entirely fulfils them. We explain how the requirements can be satisfied within the network software, in a simple manner and adequate use of the FIP protocol even if this is not very efficient. Finally, we show the requirements may be satisfied in a simple and efficient manner.<
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