It is an electric machine, which operation principles are based on eddy currents of Foucault or Eddy current that take place in electric machine operations.
Not as the electric engines where they want to reduce to the maximum these eddy currents to elevate its yield, a brake of eddy currents (Foucault ) power and it takes advantage of the parasitic currents, that take place in the stator, to offer resistance to the axis turn. The rotor is toothed assembled and when turning dragged by the engine producing in the stator currents that go against the movement under the influence of a magnetic field generated by a coil in the stator and of adjustable characteristics by electronic control.
The resistant torque is proportional to the intensity that crosses the coil and the braking power is the product of that torque times the speed of turn.
All the restrained power is transformed into heat, reason why it is necessary to cool the machine evacuating it by water circulation in mechanized "shirts" in the stator. The brakes housing or stator is balanced and would be dragged by the rotors magnetic influence in its turn, if not outside because an effort sensor or extensiometric load cell is prevented by the union of a bench. This sensor, can measure the force or torque whereupon it tries to turn the stator, that is the same one that the rotor transmits, called resistant torque and being also is the engines torque. The dynamometric brake not only offers the resistance to the turn, but also evacuates the heat generated in the process and measures the engines torque. As it is also possible to measure the speed of turn in the brake, which is same that the engines one, it is possible to obtain the mechanical power of the engine just by multiplying the torque by the regimen of turn in every moment.
The control of the brakes resistant torque is made electronically by means of a regulator P.I.D. (Proportional, Integral, Device) that applied to the power stage of suitable transistors to the type of brake, allows to stabilize the set brake-engine in conditions of predetermined torque and regime, manually or of automatic commanded form from the computer according to a work cycle programmed by the user.
The electric dynanometers are easily adjustable and very stable, but their dimensions based on the disipable power are very elevated, which is reflected in its cost. For less precise applications and cost, there are sometimes used, electric brakes of cooled air Foucault, that allow a reasonable power opposion although by short periods of time as being limited by their ventilation.
