The OCS Filter Pressure Test (FPT) determines the Filter Pressure Value (FPV), i.e. the pressure rise measured over time upstream of the screen filter as an indication of the melt purity or dispersibility of added colour pigments. The OCS Measuring Extruder (ME) melts and homogenises the test material, which is then delivered to the filter via a melt pump at a defined and constant volume flow. The increasing pressure of the polymer melt is displayed, continuously recorded and finally evaluated.