The principle of the eddy current dynamometer is based on a simple interaction. As soon as current flows through the excitation coil, a magnetic current is formed whose flux lines close around the coil. If the rotor is moved within this field, eddy currents are induced in the sides of the cooling chamber. These eddy currents construct a counter-magnetic field which then brake the rotor. The influx of mechanical energy is thereby transformed into heat and led off by the water.