I. FUNCTIONS AND CAPABILITIES
1. Basic Concept Description:
The Series 210 Residual Analyzer uses a Galvanic measurement
cell consisting of a Cathode and a Copper Anode with the sample water as the electrolyte. This
measurement method is referred to as Amperometric and has been in use for over 50 years.
As described below, the measurement cell can be used to measure the concentration of Free
Chlorine, Total Chlorine, Chlorine Dioxide and other oxidants. Certain chemical species produce
an electrical current in the cell that is proportional to their concentration in the sample water. This
electrical current is read and manipulated by the Series 210 monitor circuit board. The system
employs a motor to continuously clean the measurement cell by the abrasive action of Tefl on balls.
Sample water continuously fl ows through the measurement cell at a controlled rate. A Temperature
sensor is employed to compensate for signal fl uctuations caused by Temperature changes. The
pH of the sample water is either manually entered for pH compensation in the software or else a pH
buff er feed system is used to control the pH in the sample water. If Total Chlorine, Chlorine Dioxide,
or some other oxidants are being measured, then another chemical will be continuously injected into
the sample water prior to its entering the measurement cell.
This analyzer is also equipped with a complete PID Control program, which can be enabled or disabled
as desired. The program accepts a proportional (fl ow) analog 4-20 mA input and uses the residual
value produced by the analyzer. This control program can be enabled as proportional (fl ow pacing),
set-point (residual) or PID (compound loop) control.
2. Galvanic Cell Theory:
Pure water has a relatively low conductivity. However, the presence of ionizing
species increases the conductivity. If two electrodes are immersed in a solution containing chemical
species (ions) capable of being reduced (gaining electrons) then this species can move toward
the cathode where it can accept electrons from the cathode. To balance this fl ow of electrons
(current), an oxidation reaction (where an oxidizable species loses electrons at the same rate) must
simultaneously occur at the anode surface.
As the reactions occur at the surface of each electrode, the local concentration of the reducible/
oxidizable species drops, thus creating local concentration gradients. As a result of the
concentration gradients, the process of diff usion moves more of these species toward the
electrodes. The rate at which diff usion moves these species to the electrode surfaces is referred to
as the rate of arrival.
The electrical current produced in the cell is proportional to the rate of arrival of the reducible/oxidizable
species at the electrodes. As the concentration of these species increases, so does the rate of
arrival. Also, as the temperature increases, the rate of arrival increases for a given concentration.
After some temperature compensation, the current is therefore an indication of species concentration.
The current is read by electrically connecting the cathode and anode.
3. Chlorine Chemistry:
When Chlorine dissolves in water it forms Hypochlorous Acid according to the
following reactions:
Chlorine Gas: Cl
2
Cl
2
+ H
2
O
↔
HOCl + HCl
Sodium Hypochlorite: NaOCl
NaOCl + H
2
O
↔
HOCl + Na
+
+ OH
–
Calcium Hypochlorite: Ca(OCl)
2
Ca(OCl)
2
+ 2H
2
O
↔
2HOCl + Ca
++
+ 2OH
–
3
Содержание 210 Series
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