Distributed I/O bus controls and supervises each cabinet fan separately. It detects malfunctioning fans and indicates them with warning or fault messages. The control program performs identification run for cabinet fans to detect nominal speed values of the fans.
Typically, the control unit of the supply unit acts as an I/O bus master. Cabinet fans in drive cubicles are controlled with separate PWM (pulse-width modulation) outputs. When the control program detects a malfunctioning fan and delivers the warning code from the supply unit to the inverter unit.