47
APPENDIX A…
A1.1
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:
G
t2
– G
t1
G
t1
(t
2
– 25) – G
t2
(t
1
– 25)
∝
=
Where:
G
t2
= conductivity measurement at a
temperature of t
2
°C
G
t1
= conductivity measurement at a
temperature of t
1
°C
One of these measurements could be made at the ambient
temperature and the other obtained by heating the sample.
Temperature coefficient (%/°C) =
∝
x 100.
For ultra pure water applications the temperature compensation
equation becomes,
G
imp1
– G
imp2
[G
imp2
(t
1
– 25) – G
imp1
(t
2
– 25)]
∝
=
Where: G
imp1
= G
t1
– G
upw1
G
imp2
= G
t2
– G
upw2
A2
Relationship Between Conductivity and
Total Dissolved Solids (TDS) Measurement
The TDS factor (i.e. the relationship between conductivity
(µS cm
–1
) and TDS in p.p.m.) is totally dependent on the
properties of the solution being measured.
In simple solutions where only one electrolyte is present, the
conductivity/TDS ratio can easily be ascertained, e.g. 0.5 in the
case of sodium chloride. However, in complex solutions where
more than one electrolyte is present, the ratio is not easily
calculated and can only be reliably determined by laboratory
testing (e.g. precipitation and weighing). The ratio in these cases
is found to vary between approximately 0.4 and 0.8, depending
on the chemical constituents, and is constant only when the
chemical ratios remain constant throughout a particular
process.
In cases where the TDS factor cannot be determined easily, refer
to the supplier of the particular chemical treatment being used.
Fig. A.1 Ultra-pure Water Temperature Compensation
Temperature ºC
0
10
20
30
40
50
60
70
80
90
100
micr
oSiemens/cm
0.1
0.0
0.2
0.3
0.4
0.5
0.6
0.7
0.8
µ
S cm
–1
A
B
Curve 'A' – Theoretical ultra pure water conductivity
Curve 'B' – High purity water conductivity
(ultra pure water with slight impurity)
Summary of Contents for AX411
Page 1: ...AX400 Series User Guide Model AX411 Dual Input Conductivity Analyzer ...
Page 53: ...51 NOTES ...
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