Correct handling of the Start button is crucial for the safety and efficiency of automation systems. With the right monitoring and diagnostics, potential problems can be recognised and rectified at an early stage.
The start button is pressed and released in a process logic. Both signal changes of the sequence are queried to ensure safety. Possible causes of manipulation of the start button can be, for example, contamination, a mechanical defect or deliberate manipulation.
Process in the logic layer:
Two zones are created in the system layer, an input zone and an inverted input zone, in order to be able to query both signal changes.
The first zone is created and all properties are named using "Fast Rename". The name is entered here under "New Text" and activated with "Apply". As a result, everything necessary is named immediately. The zone is then cloned with "Clone to invert" to transfer all properties.
If further steps are added, the Start button can be handled differently depending on the requirements.
Option 1: All further operands are declared with 0 - don't care. As a result, each further press of the Start button has no effect on the process.
Option 2: All other operands are monitored with I - Interlock Check. This serves as a kind of panic function that stops the automatic system when the Start button is pressed again.
Option 3: All other operands are monitored here with M - Monitoring Check. This is used to diagnose or monitor the status of the push-button. Each button press is recorded in the alarm log file in the HMI.
