Design And Function - ProMinent CLE 3-mA Instrucciones De Servicio

Design and function

3
Design The CLE chlorine sensor is a membrane-covered, two-electrode sensor. It
consists essentially of the membrane cap and the electrode shaft. The
electrolyte-filled membrane cap forms the measurement chamber. A micro-
porous membrane in the membrane cap allows gases in the sample water to
pass into the membrane chamber. The electrodes in the electrode shaft
project into the measurement chamber. The amplification electronics are
located above the electrodes in the electrode shaft. The electrical connector
is located above the electronics.
The measurement gauge for temperature compensation is integrated into the
lower end of the electrode shaft
Measured variable Free chlorine (HOCl, OCl
hypochlorous acid (HOCl) and hypochlorite (OCl
chlorine. In the operating range of the CLE probe (pH 5.5...8) disinfection is
carried out almost entirely by the hypochlorous acid. The chlorine sensor
detects only the hypochlorous acid (HOCl) as a proportion of the free active
chlorine. The hypochlorite (OCl
disinfectant, is not measured.
Function The CLE chlorine sensor is a membrane-covered amperometric two-
electrode sensor. A gold cathode acts as a working electrode and a silver
chloride anode is the counter electrode. After connecting the probe to the
controller a constant polarisation voltage is passed to the electrodes. The
hypochlorous acid diffuses through the membrane and depolarises the
working electrode. The resulting current flow (depolarisation current), which
under constant conditions is proportional to the concentration of the
hypochlorous acid, is converted by the probe electronics into a standard
output signal (4...20 mA) and is displayed by the measuring device/
controller.
The equilibrium of the system HOCl/OCl
can see from Fig. 1, the HOCl concentration falls rapidly as the pH increases.
At pH 7, for example, the proportion of hypochlorous acid (HOCl) in the free
chlorine is approx. 77 % but only 25 % at pH 8.
As the CLE measures only the hypochlorous acid, the measurement signal is
equally dependent on the pH value.
Fig. 1
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Design and function
-
, Cl ). The sum of the chlorine gas (Cl
2
-
) is described as free active
-
), which is 100 times less effective as a
-
is strongly pH-dependent. As you
DPD-1 reagent is normally used to
calibrate the CLE chlorine sensor.
However, this measuring method
always detects the sum of HOCl and
-
OCl . Therefore the pH value must be
kept constant after calibration. If the
pH value has altered by more than
±0.2 since the previous calibration
the probe must be recalibrated. If the
pH value of the sample liquid cannot
be kept constant you should use a
controller which can automatically
correct the pH value of the chlorine
signal.
),
2
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