Data
77
Ion component of sample
It becomes difficult to measure residual chlorine in high metallic ion concentration. If the
cathode is plated by metals, clean the electrode in accordance with the “ Removal of sensor
contamination ” (page 49) or replace the cathode.
It is recommended to make electrochemical cleaning often for the sample high metal ions are
included.
Note
When the sensor is replaced, also replace all the beads.
After replacing the sensor, warm up (for break-in) for at least 3 h and then start the calibration.
Electrochemical cleaning capability
The HR-200 uses an electrochemical reaction to measure the concentration of residual
chlorine. General tap water, swimming pool water, and bath water contain metallic ions. When
metallic ions reach the surface of the cathode electrode, metallic ions receive electrons and
will be reduced to metal which is plating on the cathode surface. For example, a ferric ion (II)
is reduced by receiving two electrons and then iron will be plated on the cathode surface.
(equation 3).
Fe
2+
+ 2
e
→
Fe... Equation 3
When metal is plated on the surface of the cathode electrode, the measured value is affected.
The electrochemical cleaning is performed to remove metal adhering to the surface of the
cathode electrode. In the electro chemical cleaning procedure, plated metals on the cathode
surface is oxidized and dissolved giving positive potential to the cathode electrode against the
electrochemical cleaning electrode. On the other hand, the electrochemical cleaning electrode
is negative potential, emits electrons and reduces the positive ion to be neutral that is metal
will be plated on the electrochemical cleaning electrode. However, since the electrochemical
electrode is not used to measure the concentration of residual chlorine, the measured value is
not affected.
The electrochemical cleaning dissolves not only metals on the cathode but also gold of the
cathode electrode. Excessive cleaning will corrode cathode electrode and shorten the life of
cathode electrode.
h19136 | UTC 2020/03/30 3:34:51
CONFIDENTIAL
