Titra
Lab
®
TitraLab 870 Reference Manual
Page 273
7. Conductivity measurements
To determine a conductivity value, the TIM870 performs the following operations in this order:
1.
Measurement of the G
S
conductance (value displayed live).
2.
Cable correction (cable resistance and cable capacity correction): G
m
corrected
conductance value.
3.
The cell constant is used to calculate the
κ
conductivity at the T sample temperaure
(measured or entered).
4.
Temperature correction: conductivity recalculated at the T
ref
reference temperature or at
25°C depending on the method programmation.
7.1 Cable correction
The cable correction takes into account the cable resistance and the cable capacitance.
1. Cable resistance
The influence of the cable resistance on the G
m
measured conductance is as follows:
Where:
•
G
s
= conductance of solution (S)
•
R= cable resistance (
Ω
)
The cable resistance is entered upon creating a 2 or 3 pole conductivity cell. Enter a cable
resistance of 0 for a 4-pole conductivity cell. This value cannot be changed afterwards.
Refer to "Create electrode", page 87.
2. Cable capacity
The cable capacity influences the measurements of very low conductance. The TIM870
performs a cable capacity correction when low conductance are measured (< 4 µS).
The equation used by the TIM870 enables an accurate measurement correction to be
obtained for cable capacities up to 1000 pF.
The cable capacity is entered upon creating the electrode. This value cannot be changed
afterwards.
Refer to "Create electrode", page 87.
(
)
S
S
m
G
R
G
G
×
+
=
1
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