Definition of Conductivity
Electrical Conductivity is the ability of a solution to conduct an
electrical current. Current flow in liquids carried by ions is different
from metals, where is carried by free electrons. Ions are formed
when a solid such as salt is dissolved in a liquid to form electrical
components having opposite electrical charges. The sodium
chloride separates to form Na+ and Cl- ions. All ions present in the
solutions contribute to the current flowing through the sensor and
therefore, contribute to the conductivity measurement. Conductivity
can be used as a measure of the concentration of ions present in
Electrical conductivity is the reciprocal of electrical resistivity.
Electrical resistivity uses the unit of ohm meter or © x m. Rather than
use the units © 1 x m 1, in 1971 the unit “ siemens” ( symbolized by the capital letter S) was adopted by the General Conference on
Weights and Measures as an SI derived unit.
The unit for electrical conductivity becomes siemens per meter. The
siemens unit is named after Werner von Siemens, the 19th century
German inventor and entrepreneur in the area of electrical
engineering. Previously to the siemens per meter unit, mho/ cm was
used to measure conductivity, where the unit “ mho” is a reciprocal
ohm. The “ mho” is the “ ohm” spelled backwards. Because of the
history of conductivity, micromho/ cm and millimho/ cm is commonly
translated to microsiemens/ cm and millisiemens/ cm because they
The unit of measurement commonly used is one millionth of a
Siemens per centimeter ( micro-Siemens per centimeter or ¼ S/ cm) .
When measuring more concentrated solutions, the units are
expressed as milli-Siemens/ cm ( mS/ cm) . For ease of expression,
1000 ¼ S/ cm are equal to 1 mS/ cm. Often times conductivity is
expressed simply as either micro or milli Siemens.