B.6 Redundancy
FOUNDATION™ fieldbus is also a distributed control architecture that provides increased
availability compared to centralized control architectures. But as a Linking Device acts
as gateway between H1 links and the HSE subnet, it represents a bottleneck concerning
the availability of communication paths leading from HSE to H1 and vice versa.
To improve the availability of the LD 810HSE Ex, it is possible to combine two Linking
Devices, which then form a redundant set of Linking Devices that logically behaves like
a single Linking Device.
B.6.1 Redundancy Concept
Hub/Switch
Redundancy Link Interface
Power Supply Power Supply
Linking Device 1
Linking Device 2
H1 Links
HSEHSE
Figure B.1: System Topology
A redundant set of Linking Devices consists of two physical Linking Devices that are
connected to the same HSE subnet and to the same H1 links. The redundant set of
devices behaves like one logical Linking Device. By duplicating the physical Linking
Device, it is possible to tolerate one fault in one of the two devices.
In a redundant set of devices, one Linking Device acts as primary device and performs
actively all communication functions including the Link Active Scheduler (LAS) function
on the H1 links. In a redundant set, it is the primary device that has to be addressed by
hosts and configuration tools.
The second Linking Device, named secondary device, acts as backup device. It receives
automatically the same configuration as the primary device, but uses different node
addresses on the H1 links and a different IP address on HSE.
The secondary device is able to take over the function of the primary device if the primary
device fails. In that case the Linking Device is reduced to a non-redundant system that
is not able to tolerate any further failure. Therefore, it is necessary to replace the defective
device as soon as possible to recover redundancy.
2PAA114135-610 105
B Technical Reference
B.6 Redundancy
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