Chauvin Arnoux CSD 22 Notice De Fonctionnement page 22

3. PRINCIPLE OF THE CONDUCTIVITY
The electrical conductance, G, of a liquid depends on the geometry of the volume
of liquid involved. It is the reciprocal of the resistance, R. It is expressed in Siemens
(S).
γ
The conductivity
per centimetre. The conductivity
conductivity of a column of liquid 1cm long having a cross-sectional area of 1cm2.
The conductivity of an electrolyte depends only on its nature and its concentration.
Just as the resistance and the resistivity are related by the formula : R = ρ (I/S)
The conductance and the conductivity are related by the formula : G =
Where G conductance in Siemens
γ
conductivity in S.cm
S area in cm
I length in cm.
The conductivity of an electrolyte can be measured simply by maintaining a fixed
alternating voltage on the terminals of the cell and measuring the current that flows
through it.
3.1 CHARACTERISTICS OF THE MEASUREMENT CELL
The conductometry cell comprises two square plates (5mm on a side) of platinum-
plated platinum, plane, parallel, and 4mm apart. The smooth platinum plates are
platinum-plated, in other words covered with platinum dendrites to form a large
porous surface area. The purpose of this operation is to limit polarization of the
electrodes.
The measured conductance of an electrolytic solution depends not only on the
conductivity of the volume of solution exactly between the plates of the sensor, but
also on the solution near this cubic volume, because the measurement cell is
immersed in a larger volume of solution.
MEASUREMENT
G = 1 / R ; 1 S = 1 Ω
is the reciprocal of the resistivity, ρ. It is expressed in Siemens
γ
is a specific characteristic of a liquid. It is the
γ
= 1 / ρ ; 1 S.cm
2 .
-1
-1 = 1 (Ω.cm)
-1 .
22
-1
γ
(S / I)