C200
S
OFTWARE
Instruction Manual C200 Part2 A1.doc
optek Danulat GmbH
•
D-45356 Essen
•
Germany
page 107
8.2
Automatic temperature compensation conductivity
Automatic Temperature Compensation
The conductivities of electrolytic solutions are influenced considerably by temperature variations. Thus, when significant
temperature fluctuations occur, it is general practice to correct automatically the measured, prevailing conductivity to the
value that would apply if the solution temperature were 25°C, the internationally accepted standard.
Most commonplace, weak aqueous solutions have temperature coefficients of conductance of the order of 2% per °C
(i.e. the conductivities of the solutions increase progressively by 2% per °C rise in temperature); at higher concentrations
the coefficient tends to become less.
At low conductivity levels, approaching that of ultra-pure water, dissociation of the H2O molecule takes place and it
separates into the ions H+ and OH–. Since conduction occurs only in the presence of ions, there is a theoretical
conductivity level for ultra-pure water which can be calculated mathematically. In practice, correlation between the
calculated and actual measured conductivity of ultra-pure water is very good.
The generally accepted expression relating conductivity and temperature is:
Gt = G25 [1 + (t – 25)]
Where:
Gt = conductivity at the temperature t°C
G25 = conductivity at the standard temperature (25°C)
τ
= temperature coefficient per °C
When making temperature compensated measurements, a conductivity analyzer must carry out the following
computation to obtain G25:
(
)
[
]
25
t
1
G
G
t
25
−
τ
+
=
Calculation of Temperature Coefficient
The temperature coefficient of a solution can be obtained experimentally by taking non-temperature compensated
conductivity measurements at two temperatures and applying the following expression:
(
)
(
)
25
t
G
25
t
G
G
G
1
2
t
2
1
t
1
t
2
t
−
−
−
−
=
τ
Where: Gt2 = conductivity measurement at a temperature of t2°C
Gt1 = conductivity measurement at a temperature of t1°C
One of these measurements could be made at the ambient temperature and the other obtained by heating the sample.
Temperature coefficient (%/°C) =
τ
x 100.
