User manual
ABS-A02-BA-e-1010 17
6.2 Influence Factors for Measurement Errors
6.2.1 Air bubbles
A small bubble of, for example, 1mm
3
will have a considerable influence on the
measurement if the sample is small. Buoyancy will be increased by approximately
1mg resulting immediately in an error of 2 digits. Hence, it has to be ensured that no
air bubbles cling to the solid immersed in the fluid. The same applies to the glass
sinker that is immersed in the test fluid.
Take great care when removing air bubbles by swirling, to prevent the fluid from
spurting out and splashing onto the sifting bowl or from water splashing. Moisture on
the suspension bracket of the sifting bowl results in increased weight.
Do not touch the solid sample or glass sinker with bare fingers. An oily surface
causes air bubbles when immersing the specimen in fluids.
Do not place solid samples (in particular flat objects) in the sifting bowls outside the
liquid as this would result in air bubbles when immersed together. For this reason
examine the bottom of the sifting bowl for air bubbles after the specimen had been
immersed in fluid.
6.2.2 Solid body sample
A sample possessing too great a volume that is immersed in fluid will result in an
increase in fluid level inside the glass pitcher. As a result, part of the suspension
bracket of the sifting bowl will also be immersed causing buoyancy to increase. As a
consequence the weight of the specimen in the fluid will drop.
Samples that change the volume or assimilate fluid are unsuitable for measurement.
6.2.3 Liquids
Water temperature is another factor to be taken into consideration. The density of
water changes by c. 0.01% per degree Celsius. A temperature measurement
showing an error of 1 degree Celsius results in an inaccurate fourth decimal place.
6.2.4 Surface
The suspension bracket of the sifting bowl penetrates the surface of the fluid. This
state undergoes continuous change. If the sample or the glass sinker is relatively
small, the surface tension will impair repeatability. The addition of a small amount of
detergent makes the surface tension negligible and increases repeatability.