Abstract: The invention relates to an air jet sieve device having a housing, at least one sieve for insertion in the housing, a sieve deck and chamber located below the sieve, a slotted nozzle beneath the sieve deck, a drive for the slotted nozzle, an air inlet to the slotted nozzle, an air outlet through the housing and out of the chamber located beneath the sieve deck, and a control unit to control operation of the device. The invention also relates to a method that permits not only detection of the sieving progress during a sieving process but also provides a criterion to permit establishing the sieving time. This is achieved by equipping the sieving machine with a measuring sensor through which the particles in the air outlet flow are detected triboelectrically and which are correlated with the sieving progress to permit establishing the sieving time.