22 Rockwell Automation Publication 843ES-UM001A-EN-P - February 2020
Chapter 2 Safety Concept
Install and Replace Encoders
Replacing a safety module that sits on a CIP Safety network is more complicated
than replacing standard devices because of the Safety Network Number (SNN).
Safety devices require this more complex identifier to verify that module
numbers that are duplicated on separate subnets across all networks in the
application do not compromise communication between the correct safety
devices.
The SNN is a unique identifier that is automatically assigned to each subnet in a
safety application. The same SNN is assigned to all devices on the subnet.
For example, when an EtherNet/IP adapter is used in a safety application, the
Logix Designer application project assigns it an SNN. All safety modules that are
installed with that adapter, are automatically assigned the same SNN.
However, each safety module requires a unique identifier within the same subnet.
A DeviceID is used to identify each safety module uniquely. The SNN and node/
IP address constitute the DeviceID of the safety module.
GuardLogix controllers retain I/O device configuration on-board and are able to
download the configuration to the replacement device.
Safety Application
Requirements
Safety application requirements include the evaluation of probability of failure
rates (PFH), system reaction time settings, and functional verification tests that
fulfill your required SIL level criteria. See Average Frequency of a Dangerous
Failure on page 20 for more PFH information.
Creation, recording, and verification of the safety signature is also a required part
of the safety application development process. The safety controller creates the
safety signatures. The safety signature consists of an identification number, date,
and time that uniquely identifies the safety portion of a project. This includes all
safety logic, data, and safety I/O configuration.
ATTENTION:
• Configure the replacement device properly and confirm that it operates
correctly.
• After installation of the module, a safety administrator must confirm the
installation and conduct trial operation and maintenance.
IMPORTANT If the 843ES CIP Safety encoder was used previously, clear the existing
configuration before installing it on a safety network by resetting the encoder
to factory default. See Reset an 843ES CIP Safety Encoder to Out-of-Box State
on page 26 for more information.
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