With the PISA backup module, for the first time, not only is the power monitoring of the individual outputs performed, but also the 24 V power supply voltage is monitored and protected against voltage drops. A protective shield in the input stage of the PISA module functions like an adjustable valve, allowing only as much current to pass through as needed to keep the supply voltage above 21 V. This enables a safe and uninterrupted supply for sensitive consumers when they are connected to the same power supply as the PISA module. Consumers that are less sensitive to short voltage drops or that themselves cause faults in the 24 V supply are connected to one of the four monitored outputs of the PISA module.