What are the various modes of redundancy for different topologies of fieldbus system?
The use of redundancy in a fieldbus system may be influenced by its topology, but much more by the nature of the application. In particular, the user might want to consider redundant power supplies (particularly if one power supply feeds several bus segments). Host system fieldbus I/O channel hardware could be redundant (providing two independent paths to the same bus cable), for increased reliabilty on each segment. Similarly, gateways between segments could be made redundant, if their continued operation is regarded as critical. In a fieldbus using control in the field, an important function is the LAS (link active scheduler) which controls bus traffic. The host (if there is one) normally provides this LAS function. To survive loss of the host system, it would be worth ensuring that a back-up LAS function is available in one or more of the field devices.
