User guide

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