Rockwell Automation 1756-RMxx ControlLogix Enhanced Redundancy System User Manual - Manual (Page 138)

138 Rockwell Automation Publication 1756-UM535D-EN-P - November 2012
Chapter 6 Configure the Redundancy Modules
Using Dual Fiber Ports with
the 1756-RM2/A Redundancy
Module
The dual fiber ports of the 1756-RM2/A module constitute a redundant pair of
communication channels between the partner 1756-RM2s in a redundant chassis
pair. One of the channels is termed as 'ACTIVE', while the other channel is
termed as 'REDUNDANT'. All data communication between the partner
redundancy modules is conducted exclusively over the ACTIVE channel. If or
when the ACTIVE channel fails, a 'Fiber Channel Switchover' is initiated
automatically and all data communication shifts to the REDUNDANT channel,
which then becomes the new ACTIVE channel.
Fiber Channel Switchover
Due to the fiber channel switchover, the redundant chassis pair continues to
remain synchronized even in the event of a failure of the ACTIVE channel. Any
of the following failures of the ACTIVE channel triggers an automatic fiber
channel switchover to the REDUNDANT channel, provided the
REDUNDANT channel is still operating in a normal condition:
• Signal attenuation along the fiber cable path routed between the partner
redundancy modules
• A broken or damaged fiber cable routed between the partner redundancy
modules
• Improper or loosely fit cable connector
• SFP transceiver fault
• Removal or loose connection of the SFP transceiver
• Data communication error (signalled by a failed CRC check)
Chassis synchronization is lost only when both of the channels have failed or are
disconnected.
The fiber channel switchover may occasionally extend the completion of data
communication packets between the partner redundancy modules. Therefore,
the controller's scan time may occasionally experience a delay of 10 ms or less.
Configuration
The use of dual fiber ports is entirely ‘plug & play’. There is no user configuration
needed for any of the operations of the active and redundant channels. The
firmware automatically manages the selection of active and redundant channels.
The dual fiber cables between the partner redundancy modules can be crossed
over between CH1 and CH2 without any restriction.