Chapter 7 Reference
7.1 Conductivity measurement
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●
New units (SI units)
New measurement units, called SI units, have come into use in recent
years. Accordingly, the this 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 compensation
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 temperature"), the “temperature coefficient” expresses
how much change (expressed in %) occurs in conductivity when the
temperature of the solution changes by 1ºC. The temperature coefficient
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 temperature, 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.
The meters are equipped with a built-in automatic temperature
conversion function, enabling them to automatically calculate and
display, based on the actual temperature measurement, 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
Measurem
ent value
10
µ
S/cm
⇒
1 mS/m
1 mS/cm
⇒
100 mS/m
100 mS/cm
⇒
10 S/m
