YOKOGAWA SC450G - Appendix 2 TDS Readings; Appendix 3 Calibration Solutions for Conductivity

IM 12D08N05-01E
APP-5
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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 accepted 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 conductivity 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 SC450G measures conductivity. This value can be used to display TDS values on the
maindisplay.Oneshouldusetheadditionalconcentrationtable.Pleaserefertosection5.5
for concentration measurement. The unit for the TDS reading can be set to ppm or ppb.
Appendix3 Calibrationsolutionsforconductivity
NOTE
Thissectionshouldbereadinconjunctionwiththecalibrationsection(Chapter6)and
themaintenancesection(Chapter7).Thecalibration(cellconstant)ofasensordoesnot
change unless the sensor is damaged.
It can also appear to change because of coating of the electrodes, or partial blockage.
Becausethesechangesshouldbehandledasdescribedinthemaintenancesection,it
does not make sense to regularly recalibrate the SC450G.
Acalibrationcheck,however,isanothermatter.Whentheobjectiveisclearlydenedasa
diagnostic exercise a regular check can bring an extra level of security and confidence to
the measurement.
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