ABB Symphony Harmony Series, Instruction, Page: 151 / 402

3 - 22 WBPEEUI240751C0
I/O Block
•
Stop or reset occurs.
In some cases, a reset may be enough to return the outputs to
normal operation. If a reset does not, then an I/O module
replacement will most likely be required. Table
3-1 summa-
rizes the I/O block output channel conditions based on type of
event.
Short Circuit Protection
Most I/O blocks incorporate some type of current limiting
where appropriate to protect against short circuits in the field
wiring. This current limiting often makes I/O fusing unneces-
sary. The current limiting prevents excessive current levels at
faulted terminals which could cause circuit damage. Specifi-
cally, I/O block channels are protected against shorts across
the transmitter or load, across positive and negative terminals,
from the positive terminal to ground, and from the negative
Table 3-1. I/O Block Failure Mode Output Conditions
Event Output Condition
Loss of all power Failure state
MFT time-out Failure state
Redundant I/O module failure
Primary
Backup
Backup assumes output control
No effect; outputs under primary control
Loss of communication:
Hnet (primary)
Hnet (backup)
Hnet (both redundant I/O modules)
Harmony controller
Backup assumes output control
No effect; outputs under primary control
Default state
Default state
Reset Failure state
Channel error Error dependent