A METHOD TO TEST THE RELIABILITY OF SIZE GRADING BY SIEVES IN SEED TESTING USING A STANDARDIZED REFERENCE SAMPLE

Standards for the apertures of sieves as set by ISO and DIN cannot gua rantee high accuracy of seed grading, because they consider only one s ource of variation of grading, but they can significantly add to accur acy and should be observed in manufacturing sieves. Calibration of gra ding by a standardised reference sample includes all sources of variat ion of the whole grading process and therefore should be used for test ing actual grading performance. For this purpose glass beads are most suitable to use as a standard reference sample, because they show cons tant properties and a high resolution. To demonstrate the utility of t he calibration of grading by a standardised referencde sample, results of a comparative test as well as results of additional experiments ar e presented. Different methods to establish standards for grading equi pment are discussed and starting-points for improving accuracy of size grading are presented.