Rockwell Automation 1791DS-IBxxxx Guard I/O DeviceNet Safety Modules - Manual (Page 115)

Rockwell Automation Publication 1791DS-UM001J-EN-P - May 2013 115
Chapter
7
Considerations When Replacing Guard
I/O Modules
This chapter provides things to consider when replacing Guard I/O modules
when they are connected to GuardLogix or SmartGuard controllers. For more
information, refer to the controller user manuals listed in the Additional
Resources on page
10 .
Considerations When
Replacing Guard I/O Modules When Guard I/O modules are connected to a GuardLogix or SmartGuard
controller, consider the following when replacing the modules.
The topic of replacing a safety I/O module that sits on a DeviceNet network is
more complicated than standard devices because of the safety network number
(SNN). The node number (Mac ID) and SNN make up the safety node’s
identifier. Safety devices require this more complex identifier to guarantee that
duplicate node numbers do not compromise communication between the correct
nodes.
The DeviceNet network supports 64 node numbers, so if you have 100 devices
on multiple DeviceNet networks, there are at least 36 duplicate node numbers
being used. Even though the duplicate nodes are on separate DeviceNet
networks, this must still be considered in a safety system.
In this example, the DNB scanner #1 is connected to node 5. The DNB scanner
#2 is connected to another node 5. If the cables get inadvertently crossed, the
scanners may be communicating with the incorrect node 5.
Figure 25 - Crossed Cable Example
Topic Page
Considerations When Replacing Guard I/O Modules 115
Replacing an I/O Module When Using a SmartGuard Controller 117
Replacing an I/O Module When Using a GuardLogix Controller 121
DNB #1 DNB #2 DNB #1 DNB #2
5 5 5 5