ABB Symphony Harmony Series, Instruction, Page: 156 / 402

WBPEEUI240751C0 4 - 1
Section 4
Redundancy
Introduction
This section provides a general description of block redun-
dancy, and details redundancy for specific block types. Redun-
dancy allows backup electronics to read inputs and to drive
outputs in the event of a primary failure. The backup is contin-
uously monitoring its ability to read field inputs and to drive
field outputs as a background diagnostic task.
NOTE: A CIO block cannot be redundant. However, the analog control station
(IISAC01) can be used with the CIO block to provide automatic or manual
backup. Refer to the
IISAC01 Analog Control Station instruction for further
explanation.
Description
Redundancy in I/O blocks protects against most common
power, communications, and block hardware and software fail-
ures and some I/O channel failures. A failover from primary
I/O module to backup I/O module is not instantaneous. Typi-
cally, failover should occur in less than 100 milliseconds.
Online diagnostics and readback checks are used to determine
the operating status of an I/O module. Both the primary and
the backup module perform the same diagnostics and read-
back tests. In all cases, the Harmony controller handles the
data management.
The redundant I/O modules utilize the serial redundancy link
to verify redundant hardware connection, monitor and verify
operation, resolve primary/backup modes, and to exchange
status information. Connectors and signal lines on the back-
plane of the base establish the redundancy link. The redun-
dancy link is also redundant.
For all redundant capable I/O blocks, both I/O modules are
active and both report data to and receive data from the con-
troller. Both modules contain the same device label and func-
tion code configuration. The input and output channels are
internally routed on the base to both I/O modules. If the