With the PISA backup module, for the first time, in addition to pure power monitoring of the individual outputs, the 24 V power supply voltage is also 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 necessary to keep the supply voltage above 21 V. This enables a safe and uninterrupted power 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.