KERN ABT-A01 Operating Manual

Contents

6.2 Influence Factors for Measurement Errors6.2.1 Air bubblesA small bubble of, for example, 1mm3 will have a considerable influence on themeasurement if the specimen is small. Buoyancy will be increased by approximately1mg resulting immediately in an error of 2 digits. Hence, it has to be ensured that noair bubbles cling to the solid immersed in the fluid. The same applies to the glassplummet that is immersed in the test fluid.Take great care when removing air bubbles by swirling, to prevent the fluid fromspurting out and splashing onto the sifting bowl. Moisture on the suspension bracketof the sifting bowl results in increased weight.Do not touch the solid sample or glass plummet with bare fingers. An oily surfacecauses air bubbles when immersing the specimen in fluids.Do not place solid specimens (in particular flat objects) in the sifting bowls as thiswould result in air bubbles when immersed together. For this reason examine thebottom of the sifting bowl for air bubbles after the specimen had been immersed influid.6.2.2 Solid SpecimenA specimen possessing too great a volume that is immersed in fluid will result in anincrease in fluid level inside the glass beaker. As a result, part of the suspensionbracket of the sifting bowl will also be immersed causing buoyancy to increase. As aconsequence the weight of the specimen in the fluid will drop.Specimens that change the volume or assimilate fluid are unsuitable formeasurement.6.2.3 LiquidsWater temperature is another factor to be taken into consideration. The density ofwater changes by c. 0.01% per degree Celsius. A temperature measurementshowing an error of 1 degree Celsius results in an inaccurate fourth decimal place.If the specimen absorbs the fluid or dissolves during the measurement in the fluid, adifferent fluid should be chosen. Additionally take into consideration that the fluidmight evaporate.6.2.4 SurfaceThe suspension bracket of the sifting bowl penetrates the surface of the fluid. Thisstate undergoes continuous change. If the specimen or the glass plummet isrelatively small, the surface tension will impair repeatability. The addition of a smallamount of detergent makes the surface tension negligible and increasesrepeatability.ABT-A01-BA-defsi-0710 39