An arrangement in a winnower comprising at least one rotational member (10) e.g. a disk or a cylinder, having cells for lifting seeds and other particles from a lower position to a higher position and a chute (14) for receiving the lifted material. The rotatable member is associated with at least one sensor (17) located in the flow of the lifted material supplied to the chute, for generating electric signals in dependence on impingement of material particles leaving the rotatable member and falling down into the chute. The sensor is operatively connected through a function circuit (18) to adjusting means for controlling an operational parameter of the winnower in dependence on the impingement intensity.