Allen-Bradley 1756-L6 Series, Reference Manual, Page: 63 / 134

Rockwell Automation Publication 1756-RM001I-EN-P - May 2012 63
FLEX I/O Modules Chapter 6
Using FLEX I/O Digital Output
Module To achieve SIL 2, the output module must be wired back to an input module for
monitoring.
Requirements When Using FLEX I/O Digital Output Modules
Regardless of the type of FLEX I/O output module used, there are a number of
general application considerations that you must follow when applying these
modules in a SIL2 application:
• Proof tests- Periodically (for example, once every several years) a System
Validation test must be performed. Manually, or automatically, test outputs
to make sure that all outputs are operational and not stuck in the ON or
OFF state. Outputs must be cycled from ON to OFF or OFF to ON.
Figure 34 - Testing Outputs
The control, diagnostics and alarming functions must be performed in
sequence.
• Use external relays to disconnect module power if output
de-energization is critical . To make sure outputs will de-energize, you
must wire an external method that can remove power from the actuator if a
short or other fault is detected.
• Test outputs at specific times to make sure they are operating properly .
The method and frequency of testing is determined by the type of module.
•
Wire sensors to separate input points on two separate modules that are on
different network nodes.
• Monitor the network status bits for the associated module and make sure
that appropriate action is invoked via the application logic by these status
bits.
Timer done
Output Bit
Output Bit
Timer
Fault
Application Logic
Actuator
Alarm to Operator
Fault
Monitoring Input
Monitoring Input
Output Fault
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