I/O Block Failure Mode Output Conditions - ABB Symphony Harmony Series Instruction

I/O Block
•
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
rizes the I/O block output channel conditions based on type of
event.
Table 3-1. I/O Block Failure Mode Output Conditions
Event
Loss of all power
MFT time-out
Redundant I/O module failure
Primary
Backup
Loss of communication:
Hnet (primary)
Hnet (backup)
Hnet (both redundant I/O modules)
Harmony controller
Reset
Channel error
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
3 - 22
Stop or reset occurs.
Failure state
Failure state
Backup assumes output control
No effect; outputs under primary control
Backup assumes output control
No effect; outputs under primary control
Default state
Default state
Failure state
Error dependent
3-1 summa-
Output Condition
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