7 Functional Description of the Fieldbus Modules
7-17
7.2.5 Master redundancy
Profibus module FI 830F is suitable for a Profibus master redundancy. If an AC 800F
should fail, a redundant AC 800F takes over all fieldbuses with the fieldbus
components connected to them and continues process control. This improves the
system availability. The redundant Profibus module FI 830F is connected to the
Profibus like any other Profibus node and communicates with the current Profibus
master via the Profibus.
The process data on the primary
(i.e. active) AC 800F are
permanently matched with those
on the secondary (i.e. redundant)
AC 800F via a special Ethernet
module, as described in Section
5.4.
If a change-over to redundancy
mode occurs, the Profibus
module of the secondary unit
nearly bumplessly takes over all
nodes on the Profibus and
continues process control.
Fig. 7-8 Profibus master redundancy
7.2.6 Line redundancy
No line redundancy has been implemented in the Profibus module FI 830F. If,
however, an analysis of the system availability shows the necessity of redundant
Profibus cabling, it is recommended to use a redundancy link module RLM 01. This
module connects the RS485 interface of the Profibus module to two Profibus lines.
The data are then transmitted on both lines in parallel. In the receive branch of the
RLM 01 the data are analyzed by a special ASIC, and only those from the properly
working line are further transmitted. This intelligent handling of the two redundant
Profibus lines ensures that no data are lost or corrupted when a switch-over occurs.
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