ABB Symphony Harmony Series, Instruction, Page: 157 / 402

4 - 2 WBPEEUI240751C0
Description
primary and backup I/O modules report different values for
the same channel to the controller, the controller will mark the
value as suspect. Refer to
Suspect Condition
in Section 6 for
further explanation.
Redundancy Arbitration
Primary and backup responsibilities are determined by an
arbitration process performed during startup. The redundancy
link between the I/O modules allows them to communicate
directly with each other. Basically, the first module up and
running assumes the primary role. A feature built into the I/O
block, however, ensures that the left module always assumes
the primary role and the right module assumes the backup role
as long as both I/O modules are mounted on the base when
the block starts up. The front panel status LEDs indicate
which I/O module is the primary and which is the backup.
Refer to Table
7-2 for the LED indications.
The arbitration process also insures that a labeled I/O module
becomes the primary when there is an unlabeled I/O module
in the redundant pair. After the labeled module starts up and
assumes the primary role, it will then automatically configure
the unlabeled backup module with its label so both share iden-
tical device labels.
Failover
The backup I/O module automatically assumes the primary
module’s responsibilities if the primary fails. Catastrophic fail-
ures that will cause a failover from primary to backup include:
•
Primary halts completely.
•
Primary loses block logic power (both BLP A and BLP B).
If a catastrophic failure of the primary module occurs, the
backup module will become the primary even if it has some
type of non catastrophic failure. Non catastrophic failures
include:
•
Primary’s Hnet communications fail (both channels).
•
One of the primary’s I/O channels fail.
•
Primary loses IFP or LFP field power.
If a non catastropic failure of the primary module occurs, the
failover will only occur if the backup I/O module is 100 percent