Allen-Bradley FlexLogix 1794, Reference Manual

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Publication 1794-RM001G-EN-P - December 2011
3-4 FLEX I/O Modules
The control, diagnostics and alarming functions must be performed in
sequence. For more information on faults, see publication
1756-RM001 .
General Considerations when using Any FLEX I/O Digital Output
Module
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. For additional information, refer to publication
1756-RM001 .
Figure 3.4
The control, diagnostics and alarming functions must be performed in
sequence..
•
Use of external Relays to disconnect Module Power if Output
De-energization is Critical
: To make sure outputs will de-energize,
users 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.
Timer done
Output Bit
Output Bit
Timer
Fault
Application Logic
Actuator
Alarm to Operator
Fault
Monitoring Input
Monitoring Input
Output Fault