ABB AC 800M User Manual page 91

Section 3 Fieldbus Topologies
Master redundancy
The AC 800M controller is linked to the PROFIBUS master module CI854A. When
a CI854A module fails or bus communication is interrupted, the redundancy partner
is automatically activated. A CI854A pair balances the data cyclically via the
CEX bus.
Line redundancy
Line redundancy requires a redundant transmission medium and a redundant bus
connection on the PROFIBUS master. The two transmission media are electrical
cables in the simplest case, or fibre optical cables for higher requirements. For
optimal usage of line redundancy, master/slaves/links with two bus terminals are
required.
The ABB PROFIBUS master module CI854A has a build in line redundancy. For
slaves with only a single PROFIBUS DP interface, the Redundancy link Module
RLM 01 can be used to integrate the device in the redundant line structure.
The master, slave or link detects the failure of a line and continues communication
over the intact redundant line. The requirements for line redundancy involve
immunity to open circuit, short circuit and error adaptation in respect of cables,
connectors, repeaters, media converters and links.
If the PROFIBUS slave has not been implemented a redundant PROFIBUS
interface, and 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.
Slave redundancy
Slave redundancy refers to a situation in which at least redundant links/gateways
and optionally redundant I/O modules are present. If a gateway module fails or a
disturbance in communication occurs, the second gateway module takes over the
task. The same principle applies to the I/O modules. The redundant module
continues to record and/or output measured values in the case of an error. The
connected sensors or actuators including the signal and command lines are generally
only set single.
3BDS009029R5001 B
Redundancy concepts
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