Thermo Scientific Orion Star User Manual page 75

The conductivity of a solution with a specific electrolyte concentration changes with
temperature and this relationship is described by the temperature coefficient of the
solution . The meter has a default temperature coefficient of 2 .1 percent change in
conductivity per ˚C, which is representative of many aqueous samples .
Solution (25 °C to 50 °C)
Ultra Pure Water
Salt (NaCl)
5% NaOH
Dilute Ammonia
10% HCl
5% Sulfuric Acid
98% Sulfuric Acid
Sugar Syrup
Total Dissolved Solids (TDS)
The Orion Star and Star Plus conductivity meters measure TDS as the total amount
of dissolved inorganics in a solution . The dissolved inorganics carry a current that
is measured by the conductivity probe . Since there is a direct relationship between
conductivity and TDS, conductivity readings are used to estimate the presence
of inorganics . The user must enter a TDS factor between 0 .01 and 10 mg/L in the
setup menu .
The standard method of determining TDS involves evaporating a sample to dryness
at 180 ˚C and weighing the residue . The TDS factor is calculated by taking the
residue weight and dividing it by the sample conductivity . Subsequent conductivity
readings are multiplied by the TDS factor to determine the TDS value of the sample .
Automatic Calibration
The Orion Star and Star Plus conductivity meters are capable of automatically
recognizing 100 µS/cm, 1413 µS/cm and 12 .9 mS/cm conductivity standards when
the nominal cell constant of the conductivity probe is entered in the setup menu .
Thermo Scientific Orion Star and Star Plus Meter User Guide
™
Meter Setup Menu Features
Temperature Coefficient (% / °C)
4.55
2.12
1.72
1.88
1.32
0.96
2.84
5.64
EN-69