Rockwell Automation T3411 ICS Regent Monitored Digital Input Modules - Manual (Page 23)

Monitored Digital Input Modules (T3411)
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result will remain off, eliminating a nuisance trip. Automatic
testing of the input module will detect the fault and the
associated fault bit will be turned on, allowing the voted result
to be controlled by the remaining healthy input module. The
faulted module can be removed and replaced. After replacing
the input module and performing a voted reset, the fault bit is
turned off, restoring the input configuration to the dual mode.
Programming Triple Fault Tolerant Monitored Inputs
Fault tolerant applications that include triplicated monitored
input modules should use the Voter instruction in ladder
logic. The voter instruction performs two-out-of-three voting
of triplicated inputs, storing the voted result in the defined
shared variable. Refer to the Regent User’s Guide section 5,
Working with Programs and Function Blocks for more details
on using the ladder logic Voter instruction.
Maintenance
No periodic maintenance or calibration is required for the
monitored digital input modules. There are no user
replaceable parts inside these modules.
Safety Considerations
The monitored digital input modules are TÜV certified for
Risk Class 5 safety critical inputs. Safety critical
configurations include dual and triple redundant input
modules and associated application voting methods.
In safety critical input applications using a single sensor, it is
important that the sensor failure modes be predictable and
well understood, so there is little probability of a failed sensor
not responding to a critical process condition. In such a
configuration, it is important that the sensor be tested
regularly, either by dynamic process conditions that are
verified in the Regent, or by manual intervention testing.
Redundant sensors can be used with redundant input
modules to eliminate any single points of failure and extend
fault tolerance to include the sensors.