horiba LAQUAact D-74, Инструкция по эксплуатации

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Technical note
D-74 91
●
Conductivity measurement
Conductivity is an index that expresses the ease with which electric current flows through
a material. Conductors are categorized either as electron conductors (such as metals
and other substances which use free electrons to conduct electricity) or ion conductors
(such as electrolytic solution or fused salt, which use ions to conduct electricity). This
section describes the kind of conductivity that pertains to ions, especially the conductivity
of electrolytic solution that uses water as the solvent. As shown in figure, two pole plates
with an area "a" are positioned parallel to each other, separated by distance "l". Then
solution is poured into the cell until it is full and alternating current is run between the
plates. Each positive and negative ion in the solution will migrate toward the oppositely
charged pole. The result is that current flows through the solution by means of ion
conductivity. When this occurs, resistance "R" is in inverse proportion to the area "a" of
the pole plates, as is the case with metal and other conductors, and is proportional to the
distance "l" between the two pole plates. These relationships are expressed by equation
①
, below.
..............................................................①
R: Resistance ( Ω ) r: Resistivity ( Ω ·m) a: Pole plate area (m
2
)
l: Distance between pole plates (m) J: Cell constant (m
-1
)
Resistivity is an index that indicates the difficulty with which current flows and is a
constant determined according to the solution. The inverse of "r", which is "L" (and is
equal to 1/r), is called the specific conductivity and is widely used as an index to express
the ease with which current flows. Specific conductivity "L" is generally referred to as
simply conductivity and is expressed in units of S/m.
Inserting conductivity "L" into equation
①
results in equation
②
, below.
...............................................................................②
As is clear from equation
②
, when a conductivity cell having a cell constant "J" of 1 m
-1
is used (in other words, when a conductivity cell having two pole plates that each have
an area "a" of 1 m
2
and are positioned parallel to each other such that the distance "l"
between the two plates is 1 m is used) the inverse of the resistance "R" of the solution
between both pole plates is the conductivity. Conductivity is defined in this way, but it
changes according to the temperature of the solution. The conductivity of a solution is
generally expressed as the value when the solution is 25°C.
Solution
Polar plates a m
2
x2