ELMETRON CC- 411, Руководство пользователя, Страница: 23 / 52

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8.2. The conductivity cell maintenance
In order to receive stable results, it is advisable to store the cell in water for a
few hours before the measurement, this is especially required in case of
distilled water measurements.
The conductivity cell maintenance consists mainly in accurate washing the
inside of the measuring cell with distilled water. The platinum electrodes must
not be cleaned mechanically, because this results in rubbing off the platinum
layer, what can cause decreasing of accuracy, lowering of stability and
changing of the K constant.
Measurements of liquids with oils and heavy-sediment content may cause
platinum contamination, make the measurement impossible and irreparably
damage the electrodes. In case of fat content in the measured liquids it is
possible to clean the electrodes by immersing the cell in acetone, chloroform,
fourhydrofuran or detergent.
Certain norms recommend universal liquid for cleaning cells. This is a
mixture of equal parts of isopropyl alcohol, ethyl ether and hydrocholic acid,
diluted with water in 1:1 ratio.
Breaking of the measuring cell hinders any further measurements due to
significant change of the K constant, unstable results and increase of the
dependence of the result on the position of the cell in the measuring vessel.
The cell should be immersed in such a way for the solution to fill it up and not
to include any air bubbles (single bubbles or silver coating). It is essential for
obtaining accurate results of measurements. The best way is to immerse the
cell, make a few vertical moves and thus to remove air bubbles through holes
in the upper part of the cell. If the air bubbles appear each time after the cell
has been immersed and they are difficult to remove, it is advisable to
immerse the cell in a water – washing up liquid mixture, what will lower the
surface tension and disable air bubbles to stick to the surface of the cell walls
or electrodes. After such action the cell should be washed accurately in
distilled water.