Thermo Scientific Orion Star Mode D'emploi page 73

The closer the sample temperature is to the selected reference temperature, the
more accurate the conductivity measurement will be, especially if the temperature
compensation coefficient is estimated or inaccurate .
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 .
Thermo Scientific Orion Star and Star Plus Series 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-67