Each controller is programmable because the user chooses which function blocks to use and how to connect
them. It is configurable because each Function Block has
user-defined behavior.
The most common cause for the DO over-current is a failure in the field there is a minor
probability that the IOM itself might be the cause of the problem. Given this, it is a common
behavior for Series C IOMs to always switchover in an attempt to localize the fault.
TIP
Note that the Primary switchover in most cases is done before actually experiencing the
over current condition.
If the cause for the DO over-current is a failure in the field, then the new Primary will see the same
output miscompare problem, and react like a non-redundant module would - it will:
l Detect the output miscompare generate Soft Failure 23 - Failure in OP circuit/field wiring
detected by AO/DO.
l Detect the over current and generate Soft Failure 180 - Output Short Circuit Detected
l Set the output to unpowered.
l Shed Mode to Manual control.
l Shed ModeAttr to Operator.
You should expect to see:
l One Soft Failure posted from the former Primary:
l Soft Failure 23 - Failure in OP circuit/field wiring detected by AO/DO
l A IOM Failover event
The following are likely if the fault was in the field:
o Two Soft Failures posted by the new Primary:
Soft Failure 23 - Failure in OP circuit/field wiring detected by AO/DO Soft Failure 180 -
Output Short Circuit Detected
o The output unpowered
o The channel in Manual mode
o The former Primary's output miscompare Soft Failure will Return To Normal once
both modules synchronize.
10.16.3 Electronic Short-Circuit Fault Recovery
To return the channel to normal operation the shorted device or shorted wiring must be corrected.
10.16.4 To clear the short-circuit fault:
CAUTION
Immediately after the IOM detects the fault and the DO Channel is set to OFF, it should be
safe to perform maintenance action.
Once the DO channel is set ON, no maintenance action can occur.
