Instructions
LWT-110 Bases for measurement | 6
B-H87.0.02.DB214-1.0 13 / 26
2-pole measuring cell
4-pole measuring cell
6.4.2 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 101 are available for
this purpose. In normal application conditions, semi-annual testing is recommended;
Adjustment of the measuring input [}p.19]. A system test by the manufacturer is re-
commended in case of doubt; Calibration and adjustment service.
For this purpose, also refer to
2 Adjustment of the measuring input [}19]
6.5 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.
6.5.1 NLF temperature compensation according to EN 27888
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 tem-
perature is 25 °C. The recommended application range of NLF compensation is
between 60 µS/cm and 1000 µS/cm.
6.5.2 Linear temperature compensation LIN
If the function of the temperature compensation is not known exactly, a linear temper-
ature compensation is normally adjusted in the device. Open the Configuration menu
and select the parameter TCOR. Configuration parameters LIN and TLIN correspond to
TK
lin
. Put simply, this means that the temperature dependency is approximately the
same over the considered concentration range of the solution. Temperature coeffi-
cients of 2.0 %/K are most common.
Formula
LF
Tref
=
LF
TX
/ ((1 + TK
lin
/ 100%) * (TX – T
ref
))
A temperature coefficient can be determined, for example, with measurement of a
solution at 2 temperatures, T1 and T2, with temperature compensation switched off.
Formula
TK
lin
= ((LF
T1
- LF
T2
) * 100%) / ((T1 – T2) * LF
T1
)
TK
lin
= value is entered in the Configuration menu in parameter TLIN.
LF
T1
= conductivity at Temperature 1