Rockwell Automation 1794 FLEX I/O System with ControlLogix for SIL2 - Manual (Page 30)

Publication 1794-RM001G-EN-P - December 2011
3-8 FLEX I/O Modules
The input’s OK bit preconditions a Timer run that is preset to
accommodate an acceptable fault response time and any communication
filtering lags in the system. If the inputs miscompare for longer than the
preset value, a fault is registered with a corresponding alarm.
Figure 3.7
The control, diagnostics and alarming functions must be performed in
sequence.
• Configuration parameters (for example, RPI, filter values) must be
identical between the two modules.
• The same controller must own both modules.
• Monitor the ControlNet status bits for the associated module and
ensure that appropriate action is invoked via the application logic by
these status bits.
• Wire sensors to separate input channels on two separate modules that
are on different ControlNet nodes.
Timer done
Timer
Inputs Faulted
Alarm to Operator
Inputs OK
SUB
Delta
Input 1
Low Limit ADD
Delta
Input 1
High Limit MULT
Range
Tolerance %
Delta
Inputs Faulted
LIM
Low Limit
Input 2
High Limit
Inputs OK