Design issues for Ethernet in automation

In modern process control systems the different activities are organised by structuring plant as a hierarchy of functional levels. In order to take into account the different requirements of the traffic exchanged at the various levels in the hierarchy, communication architectures are also organised as levels of networks using different communication protocols according to their specific operating conditions. The heterogeneous nature of these networks, however, causes problems of incompatibility and complicates the exchange of information between different levels. For this reason, manufacturers and users are currently showing great interest in harmonising the communication infrastructure at the plant level, and Ethernet technology seems to be the most natural candidate for a number of practical and economic reasons. The paper addresses some issues about the use of Ethernet as a single network technology in a process control system, especially focusing on how to improve timeliness in the delivery of real-time data over a shared Ethernet network used at the field level. Two suitable approaches are presented and evaluated using simulation. One of them is priority-based, while the second is based on adaptive traffic smoothing.