4 Cabling the AC 800F
4-64
4.3.1.3 Connecting a Profibus master redundancy
The Profibus module FI 830F is suitable for Profibus master redundancy. The
redundant AC 800F accommodating the redundant Profibus module can be
connected to the Profibus like any other Profibus node. It communicates with the
current Profibus master via the Profibus. Thus, the redundant unit is permanently
checked for proper functioning, over all communication levels. Observe the
instructions given above for connecting a Profibus via RS485.
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 the redundancy link. For this
purpose, a point-to-point connection is established between the two redundant
AC 800F. This ensures both rapid and deterministic data transfer.
Set the coding switch on the
Ethernet module to the
appropriate position to define
whether or not the Ethernet
module should have the special
features required for redundancy
communication. Refer to Section
5.4 for details.
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. 4-40 Profibus master redundancy
4.3.1.4 Connecting a Profibus 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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