Yokogawa EXAxt SC450 4-Wire Analyzer for Conductivity/Resistivity - Manual (Page 58)

50
IM 12D08N05-01E
Appendix 2
TDS readings
The concept of Total Dissolved Solids (TDS) is
widely used as an indication of the total solute
concentration in water and is a widely accept-
ed water quality standard. The determination
is simply made by evaporation and weighing
the residue. As the heat treatment converts
the chemical properties of the solution, some
solutes that contribute to the total conductiv-
ity will not be found in the residue. Also some
combinations of solutes will become volatile
at the drying temperature. The same applies
for those solutes that do not contribute to the
conductivity but do end up in the residue.
When one (or a few) solute is dominant in the
solution, these problems may be neglected
and TDS will have a direct correlation with the
conductivity. Next is a graph that shows the
correlation between the specific conductance
and concentrations (by weight) for six salts.
The factor by which the conductivity should be
multiplied to come to a TDS reading ranges
from 0.4 to 0.7 up to a conductivity of 500 µS/
cm. At a conductance of approximately 3000
µS/cm the range would be from 0.5 and 1.0.
The EXAxt 450 measures conductivity. This
value can be used to display TDS values on
the main display. One should use the addition-
al concentration table. Please refer to section
5-5 for concentration measurement. The unit
for the TDS reading can be set to ppm or ppb.
0 1000 2000 3000 4000 5000
1000
2000
3000
4000
5000
6000
7000
Concentration, mg/L
Specific conductance, µS/cm, 25°C
MgCI
2
Na
2
SO
4
MgSO
4
CaCI
2
NaCI KCI