H72.0.11.6C-04
Operating Manual GMH 3451
page 8 of 18
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The salt composition of the different seas is not the identical. Depending on place, weather,
tides, etc. there may be considerable divergences to the 35 ‰ according to IOT.
Additionally the salt composition may influence the ratio between salinity and actual salt
content.
6.6 Electrodes / measuring cells
6.6.1 Design
Basically there are two types of measuring cells: 2-pole and 4-pole cells. The operation is done similarly; the
4-pole measuring cells can compensate polarization effects and – up to some degree – soiling due to its
complex measuring method.
2-pole measuring cell
4-pole measuring cell
6.6.2 Calibration / Adjustment of measuring cells
Especially in harsh environments and over long time the cell constants of measuring cells are drifting.
Depending on the application and use we recommend a regular checking of the precision of the measuring
chain: inst cell. For this there are control solutions available (GKL 100, 101, 102). At normal use a
checking each half year is recommended (see chapter 11 Automatic adjustment/calibration of cell
correction). A system check at the manufacturer is recommended in case of doubt: see chapter 15 Accuracy
Check / Adjustment Service).
6.7 Temperature compensation
The conductivity of aqueous solutions depends on its temperature. The temperature dependency is strongly
dependent on the type of solution. The temperature compensation recalculates solutions’ conductivity to a
consistent reference temperature. The most common reference temperature is 25 °C.
6.7.1 Temperature compensation “nLF” according to EN 27888
For most applications (e.g. in the area of fish farming, surface or drinking water measurements, etc.) the non-
linear temperature compensation for natural water (“nLF”, according to EN 27888) is sufficiently accurate.
The common reference temperature is 25 °C.
Recommended application range of nLF-compensation: between 60 µS/cm and 1000 µS/cm.
6.7.2 Linear temperature compensation and determination of temperature coefficient “t.Lin“
If the actual function needed for exact temperature compensation is not known, “linear temperature
compensation” is normally selected (Menu, t.Cor = Lin, t.Lin corresponds
TK
), i.e. one assumes that the
actual temperature dependency at the considered concentration range is approximately equal:
LF
LF
1
TK
100% • Tx
Tref
Temperature coefficient of about 2.0 %/K are most common.
A temperature coefficient can be determined for example by measuring a solution with deactivated
temperature compensation at two different temperatures (T1 and T2).
TK
LF
LF
• 100%
T1
T2 • LF
TK
lin
is the value input at the menu “t.Lin”.
LF
T1
conductivity at temperature T1
LF
T2
conductivity at temperature T2
