35
5. OPERATION PROCEDURES
Water Quality Readout
Measuring electrical conductivity
Water quality gauge on control panel indicates the conductivity at the outlet of ion-exchange resin
cartridge and at the outlet of condenser for distilled water. Water quality readout for ion exchanged
water should be used as a guide to determine a time for ion-exchange resin cartridge replacement. Be
sure to read display with the electrode completely immersed in water, i.e., while dispensing ion
exchanged water. In the following cases, the electrode is not immersed in water and is affected by air
bubbles. Therefore, displayed values are not accurate.
1. When unit has just started operation, or during stop
2. Immediately after replacement of ion-exchange resin cartridge and pre-treatment cartridge
3. Immediately after the start of the distillation process
Electrical conductivity
・
Electrical conductivity (
ρ
) is a numerical value representing the ease of passing electricity. When
greater quantity of electrolytes or impurities are dissolved, water is more likely to pass electricity and
in that state the value of electrical conductivity is high.
The smaller value represents the better purity of pure water.
・
However, the value of electrical conductivity does not show the content of non-electrolytic
substances (organic substances, colloidal substances, dissolved gases, microorganisms, etc.) but
only indicates electrolytic substances. Consider it as one index of the purity of water.
・
Specific resistance (R) also indicates the flow of electric current. Specific resistance is inversely
related to the electrical conductivity. The higher value, therefore, represents the better purity of water.
R[
Ω
・
m]=
1
or
R[×10
4
Ω
・
m]=
1
ρ
[S/m]
ρ
[×10
-4
S/m]
The value of theoretical pure water is calculated as follows:
R=18.3 × 10
4
Ω
・
m(18.3 M
Ω
・
cm)25 °C
(Note that the specific resistance is represented in integers in the range of 18 to 1 × 10
4
Ω
・
m and
does not show decimal point)
ρ
=0.055 × 10
-4
S/m(0.055
μ
S/cm) 25 °C
Water quality of ion exchanged water and distilled water
・
Ion exchanged water and distilled water have the following characteristics. Use them suitably for the
purpose.
It is the best to use pure water immediately after collection. If it is not going to be used for a long
period of time, drain all the water from distilled water tank. If the water has been stored in distilled
water tank for a long period of time, drain the tank and produce distilled water once again.
(1) Ion exchanged water
Most of the electrolytes in the water are removed, resulting in water with the lowest electrical
conductivity. Non-electrolytic substances cannot be removed. More or less, the purity of water
occasionally drops while the resin is new, or when produced after extended storage of unit.
(2) Distilled water
Distillation can remove both electrolytic and non-electrolytic substances averagely, except for
substances of low boiling point such as ammonia. However, in the production process (condensation
and storage), water absorbs carbon dioxide gas in the air, and produces carbonic acid gas. This
makes electrical conductivity 1 to 2.5×10
-4
S/m (1 to 2.5
μ
S/cm) 25 °C which is worse than that of ion
exchanged water, and pH will be 5 to 6, indicating weak acidity.
See JIS K 0102 (Testing methods for industrial wastewater) for how to remove dissolved gas
(oxygen/carbon dioxide) in pure water.