<p>In a ventilating fan (1), power consumption of the driving motor (M) is utilized to detect operating condition and fault condition. By means of a sensing resistor (R1) and a fault sensing circuit (2) the power consumption is measured and converted into a two logical level information. The logical level information is coded in a two bit code (00, 10) for a system µP (4) to control power supply of the motor (M) and the device to be cooled by the ventilating fan (1).</p>
