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Measurement Basics | 5
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5.6 Electrodes / measuring cell
5.6.1 Design
There are basically two different types of measuring cells: 2-pole and 4-pole measur-
ing cells. Control and/or evaluation take place in a similar manner; the 4-pole measur-
ing cells can compensate well for polarisation effects and contamination to a certain
degree with the more elaborate measuring processes.
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The product is equipped with a permanently connected 2-pole measuring cell.
2-pole measuring cell
4-pole measuring cell
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Universal 2-pole graphite measuring cell with wide range of applications, such as fish
husbandry, measurement of surface water and drinking water.
5.6.2 Calibration / adjustment of the measuring cell
_
In harsh applications and due to ageing processes, the cell constant of measuring
cells changes. Depending on the application and precision requirement, the overall
precision of the display device and measuring cell measuring chain should be checked
regularly. Special testing and calibration solutions, such as GKL 100, 101 and 102 are
available for this purpose. In normal application conditions, semi-annual testing is re-
commended;
Adjustment of the measuring input [
. A system test by the man-
ufacturer is recommended in case of doubt; Calibration and adjustment service.
For this purpose, also refer to
2
Adjustment of the measuring input [
5.7 Temperature compensation
The conductivity of aqueous solutions is temperature-dependent. The temperature de-
pendency varies greatly according to the type of solution. With temperature compens-
ation, the solution is calculated back to a uniform temperature in order to compare it
independently of the temperature. The normal operating temperature for this is 25 °C.
_
However, it can also be adjusted to 20 °C.
5.7.1 NLF temperature compensation according to EN 27888
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For most applications, such as fish husbandry applications and measurement of sur-
face water and drinking water, non-linear temperature compensation for natural water
NLF
is sufficiently accurate in accordance with EN 27888.
The normal operating temperature is 25 °C.
The recommended application range of
NLF
compensation is between 60 µS/cm and
1000 µS/cm.
