Fieldbus & Industrial Networking


Redundant fieldbus communications

March 2006 Fieldbus & Industrial Networking

As fieldbus networks enter more and more into the mission critical domains of availability and redundancy of both the network path and the I/O devices, the pressure on fieldbus networks to deliver more is increasing. Omniflex has produced a number of solutions for demanding applications using its Conet Fieldbus Network and Maxiflex, its programmable I/O system platform. This is a fully redundant system comprising dual redundant network systems ie, dual master nodes, dual Conet networks and dual front end I/O nodes. (The figure shows the system makeup.)

The system is made up of a primary link and a secondary link. Each link includes a master node that is responsible for connecting the scada system to the I/O node in the same link. The master nodes are also the nodes responsible for ensuring the integrity of the entire system so that there is always communications between the scada system and an I/O node. In order to accomplish this, each master node is connected via Conet to a Conet NIM module that is fitted into the Maxiflex rack of the other master node. As the Conet NIM modules are electrically isolated from the Conet network, the primary Conet Lan and secondary Conet Lan are isolated from themselves, providing complete dual redundancy from the master nodes through to the I/O nodes.

The primary link is used by the scada system during normal operation. The primary master is continuously checking all relevant communication and I/O node status indicators to ensure the link is healthy. In the event of a failure in one or more status indicators, the primary system will flag this to the scada system and this condition will be detected by the secondary master node. At this point the secondary system will 'take control' of the communications link until the primary link is restored. Once the primary link is restored, the secondary link will 'release control' of the communications link to the primary system.

Both master nodes must be downloaded with the redundant link software for the system to operate. No redundant software is required to be downloaded to the front end I/O node thereby keeping these nodes free for any user application required.

A number of different solutions, including Ethernet with hot standby on applications for top ends, are available to suit application constraints imposed by the end user. Contact Omniflex directly to discuss your application.



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