Limit value monitor

The FB_LimitMonitor function block reliably monitors an actual value for compliance with defined lower and upper limits and simultaneously saves the minimum and maximum values reached. The block is fully implemented in Structured Control Language (SCL) and is ready for immediate use in the Siemens TIA Portal.

Note: All modules are designed exclusively as a learning and optimization basis and are not approved for live operation. System modules, in particular, must be finally tested and commissioned by qualified personnel before productive use.

At the beginning, the logic checks whether the IstWert is below the UnterGrenze or above the OberGrenze :

• Lower limit or upper limit = TRUE if outside
• ImGrenzbereich = TRUE if within

When Init signal is active, the first recorded actual value is simultaneously set as the minimum and maximum value. Starting in the next cycle, the block compares the actual value with the stored extreme values and updates them as needed.

The StatusText reports depending on the status:

• “Value below limit”
• “Value above limit”
• “Value within the normal range”

• Inputs/Parameters: IstWert , UnterGrenze , OberGrenze (REAL), Init (BOOL)
• Outputs/Variables: UnterGrenzwert , OberGrenzwert , ImGrenzbereich (BOOL), Minwert , Maxwert (REAL), StatusText (STRING)
• Implementation via simple comparison logic without timers or state machines

• Process monitoring in production plants
• Extreme value recording in test benches and test systems
• HMI visualization of limit violations in real time
• Support for maintenance through transparent status messages

• Siemens S7‑1200 & S7‑1500 controllers
• Developed for TIA Portal from version V13
• Simulation & HMI connection recommended from TIA Portal V16

You will receive the .scl file with complete declarations of all inputs and outputs. Customization instructions for initialization and limit definition are included in the code header. The download link will be available immediately after purchase.

I would be happy to support you in fine-tuning the limit ranges, integrating additional functions for extreme value detection or visualizing them in the HMI.

Just contact me via shop message or email for individual customizations.