LaMotte CON 6 PLUS Manual page 30

particularly where high purity water is involved. The unit most
often used to describe resistivity is megohm-cm, which are simply
the reciprocal of conductivity (μS/cm). The chart below shows the
relationship between these units.
Conductivity and Temperature
Conductivity in aqueous solutions refl ects the concentration, mobility,
and charge of the ions in solution. The conductivity of a solution will
increase with increasing temperature, as many phenomena infl uencing
conductivity such as solution viscosity are aff ected by temperature.
The relationship between conductivity and temperature is predictable
and usually expressed as relative % change per degree centigrade.
This temperature coeffi cient (% change per degree) depends on the
composition of the solution being measured. However, for most medium
range salt concentrations in water, 2% per degree works well. Extremely
pure water exhibits a temperature coeffi cient of 5.2%, and concentrated
salt solutions about 1.5%.
Since temperature aff ects the conductivity measurement so profoundly,
the usual practice is to reference the conductivity to a standard
temperature—typically 25 °C. Select 20 °C or 25 °C as the normalization
temperature in advanced setup.
Enter the temperature coeffi cient which best suits the sample and use an
ATC probe to automatically temperature compensate back to the chosen
reference temperature.
Conductivity
(μS/cm)
0.056
0.1
1.0
2.5
10.0
Resistivity
(megohm-cm)
18
10
1.0
0.4
0.1
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