28
Operation Method
Display of Water Quality
Measurement of Electric Conductivity
The water conductivity meter on the control panel displays the conductivity at the outlets of the
ion-exchange resin cartridge and the condenser for distilled water. The displayed value can be used
as an index for replacing the ion-exchange resin cartridge. The value of conductivity is valid only
when the electrode is fully damped with water, or when pure water is dripped. Correct value is not
displayed in the following cases because the electrode is not damped or air bubbles are produced.
1. At beginning of operation and during halts
2. Just after changing pretreatment cartridge or ion-exchange resin cartridge
3. Just after distillation starts
Electric conductivity
Electric conductivity is a value indicating easiness of flowing of electricity. In the case of water,
electricity flows the more easily when the more electrolyte i.e. impurity is solved, so the value of
conductivity is the greater; when the less electrolyte is solved, the smaller is the value.
When the value of electric conductivity is the smaller, the better is purity of pure water.
Here, electric conductivity indicates only electrolyte, and does not indicate content of
non-electrolyte (such as organic substance, colloid substance, dissolved gas, and microorganism),
and it is just an index indicating purity of pure water, and it does not represent all of purity.
Specific resistivity indicates the same contents as electric conductivity. Specific resistivity is
inversely related to electric conductivity, and when the value is the greater, the better is purity.
When obtaining specific resistivity from electric conductivity, where specific resistivity is
R
and
electric conductivity
ρ
,
R［Ω･m］
1
S m］
=
ρ
[ /
or
R［×10 Ω･m］
1
×10
S m］
４
－４
=
ρ
[
/
So the theoretical value of pure water is as follows:
R=18.3
×
10
4
Ω･
m (18.3M
Ω･
cm) 25
℃
(Take notice that the resistivity is displayed in integer form (not in decimal) in the range 18 to 1 x
10
４Ω・
m.)
ρ
=0.055
×
10
-4
S/m (0.055
μ
S/cm) 25
℃
Quality of ion exchange water and distilled water
Ion exchange water and distilled water have the following features respectively. Distinguish them
as necessary in use.
It is ideal to use pure water immediately after sampling; therefore be sure to drain water in distilled
water tank if it is out of use for a long time. If water has been stored in distilled water tank for a long
time, drain once, then store in distilled water tank newly before use.
1. Ion exchange water
Most of electrolyte in water is removed, and water with the lowest electric conductivity is obtained.
However, non-electrolyte cannot be removed. In addition, slight fall of purity is found while resin is
new and when water is fed again after halt of system.
2. Distilled water
Electrolyte and non-electrolyte can be removed in average except for low boiling point substance
such as ammonia. However, carbon dioxide gas in the atmosphere is absorbed and carbon oxide
is generated in the process of manufacturing (condensing/storing), and so the electric conductivity
is worse than ion exchange water, that is 1 to 2.5 X 10-4 S/m (1 to 2.5
μ
S/cm) at 25C, and
represents weak acid (pH5 to 6).
See "2 - Common item (11) Water" of JIS K0102 (Plant drain test procedure) for removal of
dissolved gas (oxygen and carbon dioxide) in pure water.
