Functional Identifiers Of Variables - Siemens SIMATIC S7-1200 Safety Programming Manualline

3 Methods for Safety Programming
3.3

Functional identifiers of variables

Safety often uses the terms 'shutdown' or 'shutdown signals'. In practice, a safety
function is described using this terminology:
"When a safety door is opened, drive XY must be safely shut down."
However, release signals are generally programmed in the technical
implementation as a safety program. This is due to the fact that safety
interconnections are designed based on the closed-circuit principle.
If, for example, a safety door is closed, it gives the enable to switch on a safe
actuator.
Recommendation
Before the start of the project, define a uniform name of the variables with the
appropriate suffixes. The identifier reflects the meaning and purpose of the
variables in the source code context.
Choose the variable identifier such that it reflects the logic "1" state ("true").
For example, "maintDoorEnable" or "conveyorSafetyRelease".
Note
The standardized names of the drive functions (e.g., STO and SLS) according to
IEC 61800-5-2 do not comply with the above recommendation.
Safety Programming Guideline
Entry ID: 109750255, V1.0, 10/2017
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