Rockwell Automation T7408 ICS Regent+Plus DC Digital Input Modules 24VDC, 48VDC and 120VDC - Manual (Page 11)

(T7401, 02, and 08) DC Digital Input Modules
P D - 7 0 1 1 M a r - 0 6
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non-interfering and when properly configured are also
certified for Risk Class 5 safety critical inputs. Safety critical
configurations include 2oo3 and 1oo2 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.
In all safety critical configurations and applications, the DC
voltage digital input modules can be used for de-energized to
trip inputs, only if the inputs are dynamically transitioned at
a period not greater than six months.
For additional safety considerations, please refer to the Safety
Considerations section of the Regent User’s Guide.