The Ripple-Count method, patented by Elmos, makes it possible to record the revolutions without any additional sensors and to determine the position of DC motors. The basis of this method is the rotor commutation of the DC motor. The method is based on the fact that the ripple frequency is estimated using the motor current measurement and that specially adapted bandpass filter filters out the relevant area from the spectrum of the motor current. This means that detecting the wanted signal is greatly simplified and is therefore precise.
The method obviates the need for sensors, such as a Hall sensor, and other permanent magnets with their respective wiring. The customer can therefore save on a lot of individual components.
It makes sense to use ripple counter ICs for pump and fan speed controls. However, the performance of these ICs is such that they can also be used in position recognition systems for window controls e.g. in the jamming protection or for the memory function in e.g. car seats.