Rockwell Automation T3411 ICS Regent Monitored Digital Input Modules - Manual (Page 21)

Monitored Digital Input Modules (T3411)
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Field wiring open circuit or short circuit conditions are
referenced in the application program using the Fault Name
tag names defined in the I/O configuration Editor. When a
line monitor device is installed across the field switch and the
wiring is healthy, the Fault Name status is on. If there is a
short or open circuit (or there is no line monitor device
installed) the Fault Name status is off.
The status of the Name and Fault Name input variables are
summarized in Table 3 for the various field input conditions.
Table 3. Input Status for Field Input Conditions.
With Line Monitor Device
Installed
Without Line Monitor
Device Installed
Field Input
Condition Name Fault Name Name Fault Name
Switch Open OFF ON OFF OFF
Switch Closed ON ON ON OFF
Open Circuit OFF OFF Same as Switch Open
Short Circuit ON OFF Same as Switch Closed
Programming Dual Fault Tolerant Monitored Inputs
To program fault tolerant configurations using dual
monitored input modules, ladder logic is used to check the
status of the inputs and the system control relays (that report
a faulted I/O module) and provide a voted input value. Two
examples are shown below.
Normally Energized Inputs
Figure 14 shows a ladder logic rung that would be suited for
normally energized inputs that de-energize to trip.
Figure 14. Dual Voting for Normally Energized Inputs.