Hach-Lange POLYMETRON 83xx User Manual - Manual (Page 9)

2 E LECTRODES C ONDUCTIVITY P ROBE - I NSTRUCTION M ANUAL
621=183=000 Issue B 09/2010 Page 5
1. Overview
General
The probes for which the electrochemical
exchanges take place directly between the
electrode and the solution are called
"contacting" probes or "kohlrausch" probes.
They consist of two conductor electrodes
(chemically inert in relation to the solution),
insulated from each other, in a particular and
known geometrical form (cell constant), on
which an alternating voltage is applied.
Therefore a mechanism of exchange exists at
the interface of the liquid and the electrodes
and only the use of an alternating voltage with
an optimum frequency avoids saturating the
surface of the electrodes (formation of an
insulating layer reducing the flow of current, a
phenomenon known under the term of
"polarisation").
It is the total quantity of ions present in the
solution that is measured and not the type of
ion as such.
Principle of electrolytic conductivity
Ohm’s law specifies that the current circulating
in the dipole is proportional to the difference in
potential and resistance of this dipole:
I = E / R.