Transferring Operational Information To The Safety Program; Using Non-Safe Inputs In The Safety Program - Siemens SIMATIC S7-1200 Safety Programming Manualline

3 Methods for Safety Programming
3.9.2

Transferring operational information to the safety program

In many applications, it is essential that specific non-safety-related results of logic
operations are transferred from the standard user program to the safety program.
These are typically operational switch-on conditions (e.g., operational and fail-safe
switching of a motor starter) or machine states for mode preselection.
Prepare the data in the standard user program to the greatest possible extent. The
more non-safety-related logic is implemented in the standard user program, the
easier it is to implement changes to the logic relevant to the process.
3.9.3

Using non-safe inputs in the safety program

Standard inputs that are required directly in the safety program must be read
directly in the safety program. A "detour" via the standard user program should be
avoided.
The background to this is that non-safety-related signals are also included in the
application's systematic integrity. Typical examples are acknowledgment / reset
buttons or mode selectors. Which button / switch is allowed to reset which safety
function is a direct result of the risk assessment. A change of the command
devices must therefore influence the signature and must be made only
accompanied by a reassessment and an acceptance test for changes.
NOTICE
The assessment of the specific signals that influence an application's systematic
integrity and, depending on this, are evaluated in the standard user program or in
the safety program depends on the risk assessment of an application.
Safety Programming Guideline
Entry ID: 109750255, V1.0, 10/2017
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