Apparatus at a spinning preparation machine, especially a flat card, roller card or the like, for ascertaining carding process variables

In an apparatus at a spinning preparation machine, wherein a clothed roller is located opposite at least one clothed component, there is associated with the component, in contact therewith, a piezoelectric sensor which is connected to an electrical evaluation device in communication with a display device and/or switching device. In order, by simple means to make it possible to ascertain the carding intensity, the piezoelectric sensor is a structure-borne sound sensor and the electrical evaluation device is capable of determining the carding intensity from the structure-borne sound.