Here you will find an explanation and illustration of a switch in the logic layer and in the system layer.
A switch is used for various functions, in particular for starting a system. There are two different ways to use a switch.
Operation in the logic layer:
The switch is flipped in the process logic and remains active. A zone is inserted in the system layer and the signal change of the switch is expected. The I - Interlock Check is monitored in each subsequent step, but the M - Monitoring Check can also be used here. The switch must always remain on. Restarting the system is prevented by an inverted zone (switch OFF).
System layer:
