EN-69
Thermo Scientific Orion Star
™
and Star Plus Meter User Guide
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)
Temperature Coefficient (% / °C)
Ultra Pure Water
4.55
Salt (NaCl)
2.12
5% NaOH
1.72
Dilute Ammonia
1.88
10% HCl
1.32
5% Sulfuric Acid
0.96
98% Sulfuric Acid
2.84
Sugar Syrup
5.64
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 .
Meter Setup Menu Features
