Using ultrasonic frequency variation for test sieving, even powders with separating cuts of ≤300 micron can be sieved. Fitting at least one HAVER-test sieve with a frequency variation system enables such analyses.

The ultrasonic frequency variation system consists of a clamping ring, which is connected by a converter to a generator. The generator converts electrical energy into high frequency energy, which is then converted to mechanical energy by the converter and transferred to the clamping ring. Sound waves cause the test sieve frame to oscillate at high frequency. These oscillations are transferred to the test sieve cloth where they are evenly distributed.

The oscillations of the test sieve cloth reduce frictional resistance between the grains and the screen. This reduces the tendency towards blockage, resulting in increased throughput. The end of a test sieving period is clearly reached more rapidly. As a result, test sieving of some difficult products is easier and in some cases, becomes possible.