Allen-Bradley 1756-L6 Series, Reference Manual, Page: 61 / 134

Rockwell Automation Publication 1756-RM001I-EN-P - May 2012 61
Chapter
6
FLEX I/O Modules
Overview of FLEX I/O Modules There are two types of SIL2-certified FLEX I/O modules:
• Digital I/O modules
•
Analog I/O modules
FLEX I/O modules are designed with inherent features that assist them in
complying with the requirements of the 61508 Standard. For example, the
modules all have a common backplane interface, execute power-up and runtime
diagnostics, and offer electronic keying.
Using 1794 Digital
Input Modules To achieve SIL 2, two digital input modules must be used, with field sensors
wired to channels on each module. The two channels must be compared by
software before reconciling the data.
Requirements When Using FLEX I/O Digital Input Modules
Regardless of the type of FLEX I/O input module used, there are a number of
general application considerations that users 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 inputs
to make sure that all inputs are operational and not stuck in the ON or
OFF state. Inputs must be cycled from ON to OFF or OFF to ON.
•
Wire sensors to separate input points on two separate modules that are on
different network nodes.
• Configuration parameters (for example, RPI, filter values) must be
identical between the two modules.
Topic Page
Overview of FLEX I/O Modules 61
Using 1794 Digital Input Modules 61
Using FLEX I/O Digital Output Module 63
Using Analog Input Modules 65
Using Analog Output Modules 71
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