Rockwell Automation Publication 1756-RM093J-EN-P - April 2018
97
Appendix
F
RSLogix 5000 Software, Version 14 and Later,
Safety Application Instructions
De-energize to Trip System
When using RSLogix 5000™ software, version 14 safety application instructions,
all inputs and outputs are set to zero when a fault is detected. As a result, any
inputs being monitored by one of the diverse input instructions (Diverse Inputs
or Two-hand Run Station) should have normally-closed inputs conditioned by
logic similar to the logic in Rung 4 of
Ladder Logic Example 2
and
Ladder Logic
Example 3
on pages
100
and
101
. The exact logic required is both application
and input-module dependent. However, the logic must create a safety state of 1
for the normally-closed input of the diverse input instructions.
Use Connection Status Data
to Initiate a Fault
Programmatically
The following diagrams provide examples of the application logic required to
latch and reset I/O failures. The examples show the logic necessary for input only
modules, as well as input and output combination modules. The examples use a
feature of the I/O modules called Combined Status, which presents the status of
all of the input channels in a single boolean variable. Another boolean variable
represents the status of all the output channels. This approach reduces the
amount of I/O conditioning logic required and forces the logic to shut down all
input or output channels on the affected module.
Use the
Input Fault Latch and Reset Flow Chart
on page
98
to determine which
rungs of logic are required for different application situations.
Ladder Logic
Example 1
shows logic that overwrites the actual input tag variables while a fault
condition exists. If the actual input state is required for troubleshooting while the
input failure is latched, use the logic shown in
Ladder Logic Example 2
. This
logic uses internal tags that represent the inputs to be used in the application
logic. While the input failure is latched, the internal tags are set to their safety
state. While the input failure is not latched, the actual input values are copied to
the internal tags.
Use the
Output Fault Latch and Reset Flowchart
to determine which rungs of
application logic in
Ladder Logic Example 3
on page
101
are required.
Topic
Page
Use Connection Status Data to Initiate a Fault Programmatically
