208 Rockwell Automation Publication 1715-UM001J-EN-P - December 2020
Chapter 7 1715 Redundant I/O System in SIL 2 Safety Applications
Requirements for
ControlLogix-based SIL 2
Applications
Add-On Instructions
The Add-On Instructions provide a mechanism to verify the validity of data
that is transferred between the ControlLogix controller and the 1715 adapter.
When you use the Add-On Instructions, the sender of the data adds check data
to the produced data. The receiver of the data uses the check data to verify the
integrity of the consumed data.
Connection Reaction Time Limit
The Connection Reaction Time Limit (CRTL) setting defines the maximum
time that the connection can operate with old data, before substituting the
configured safe state values. If the CRTL expires, the receiver requires a SIL 2
Reset before valid data is provided again.
For an input module, if the CRTL expires before the Add-On Instruction
detects valid data, the value of the affected input assembly transitions to the
configured safe state value. A SIL 2 reset is required before inputs transition
from the safe state to field values.
For an output module, if the CRTL expires before the 1715 firmware detects
that valid output data is received from the Logix controller the output data
transitions to the configured safe state values. In this case, a SIL 2 Reset is
required before outputs can be re-energized.
Using the 1715 Adapter in
SIL 2 Applications
The 1715-AENTR adapter performs the following functions:
• External communication with the controller via an Ethernet network
• Communication with I/O modules, such as receiving input values,
sending output values, and coordinating diagnostics
• Enforcement of the output CRTL on data that is received from a
ControlLogix controller
For high availability, use two 1715-AENTR adapters in simplex and duplex SIL 2
applications.
Reaction to Faults
The 1715-AENTR adapter reports faults via status indicators that turn red when
a fault is detected in the adapter. Fault indications are also sent to the user
application. These variables provide the following information:
• Module presence
• Module health and status
• Channel health and status
• An echo of the front panel indications
IMPORTANT
To meet SIL 2 application requirements in a ControlLogix system,
you must use the 1715 Add-On Instructions that are described in
Chapter 8
.
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