to the Conductivity Theory Page.
Conductivity is the ability of a solution to conduct electric
current. The principle by which instruments measures
conductivity is simple - two plates (cells) are placed in the sample, a
potential is applied across the plates and the current is measured. Generally,
the potential is in the form of a sine wave. Conductivity is
determined from the voltage and current values according to Ohm's Law:
G=1/R=I (amps)/E (volts)
Since the charge on the ions in solution
facilitates the conductance
of electrical current, the conductivity of a solution is proportional to
its ion concentration.
Note: Some solutions may not show a direct
correlation to concentration, ionic interactions can alter the linear
relationship between conductivity and concentration in some highly
concentrated solutions like sulfuric acid.
The basic unit of measurement for conductivity is the
Siemens (S). Since
cell geometry affects conductivity values, standardized measurements are
expressed in specific conductivity units (S/cm) to compensate for variations
in electrode dimensions.
Conductivity measurements are temperature dependent. The
degree to which temperature affects conductivity varies from solution to
solution and can be calculated.
Most conductivity electrodes
only have two plates, usually made of
platinum or carbon (graphite). The EID's four plate or 'Bull's Eye'
design results in higher accuracy for measuring pure water.
The following shows optimum conductivity ranges for cells of three
CONDUCTIVITY RANGE (uS/cm)
0.5 to 400
10 to 2,000
1000 to 200,000
should be calibrated using a standard
solution before using. When selecting a standard, choose one
that has the approximate conductivity of the solution to be measured. After
using the probe for some time, you might consider cleaning the plates
with a mild liquid soap or acetone - Note: Do not
use abrasive materials in cleaning.
Waste water treatment