NAVI F-52, Instruction Manual

Page: 255 / 270

Chapter 16 Reference
16.4 Conductivity measuring
242 HORIBA
m is used l the inverse of the resistance R of the solution (expressed in
Ω
) 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 25ºC.
●
New units (SI units)
New measurement units, called SI units, have been in use since 1996. Accordingly, this pH
meter also uses SI units. The following conversion table is provided for people who are used
to using the conventional kind of conductivity meter. Note that along with the change in unit
systems, the measurement values and cell counts have also changed.
●
Temperature coefficient
The conductivity of a solution generally varies greatly, depending on the temperature of the
solution. Because the conductivity of a solution is based on its ion conductivity, as explained
above, the higher the temperature of the solution the more active its ions and the higher its
conductivity. Using a given temperature as the standard (and calling that the standard temper-
ature), the “temperature coefficient” expresses how much change (expressed in %) occurs in
conductivity when the temperature of the solution changes by 1ºC. The temperature coeffi-
cient is expressed in units of “%/ºC (standard temperature).” This temperature coefficient is
found by assuming that the conductivity of the sample changes linearly in relation to temper-
ature, whereas the change in conductivity of an actual sample, strictly speaking, follows a
curve. The shape of this curve changes, depending on the kind of sample being measured.
Most solutions, however, are said to generally have a temperature coefficient of 2 %/ºC (25ºC
standard), within a range where the size of the temperature change is not very large.
(Temperature coefficients of various solutions are listed on the following page.)
This pH meter is equipped with a built-in automatic temperature conversion function,
enabling them to automatically calculate and display, based on the actual temperature mea-
surement, the conductivity of a sample at 25ºC, using a temperature coefficient of 2 %/ºC.
Former units ⇒ SI units
Cell
constant
1 cm
-1 ⇒
100 m
-1
0.1 cm
-1 ⇒
10 m
-1
10 cm
-1 ⇒
1000 m
-1
Measure-
ment value
10
μ
S/cm
⇒
1 mS/m
1 mS/cm ⇒ 100 mS/m
100 mS/cm ⇒ 10 S/m