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Measurement / Operation
Polarization
Calibration with the
DPD-1 method
14
4
Measurement / Operation
4.1
Run-in period
Each time the sensor has been refilled it must be polarized. To do this,
immerse the connected and voltage-supplied sensor in a well-stirred chlorine
solution with at least 5 mg/l chlorine for an hour. Then put the sensor into use
(measuring position). The sensor can be calibrated after a stabilizing time of
approx. 20 minutes. After approx. one day, a post-calibration should be
performed.
The position in the flow through vessel has a considerable effect on the
approach flow and, hence, the measuring function of the sensor. Therefore
carefully position the sensor as described below.
The sensor filled with electrolyte must not become dry and has
to be permanently supplied with electrical voltage. Otherwise the
characteristics of the membrane cap, electrode finger and elec-
trolyte will be changed (sometimes irreparably). The sensor may
only be stored in an unfilled condition (see also section
5.3 S
TORAGE
4.2
Check of the sensor / analysis
The chlorine sensor has a linear characteristic curve. Calibration of the chlo-
rine sensor is carried out as a single-point calibration. The calibration value
(nominal value) is usually determined photometrically. A common procedure
for this is the DPD method for free chlorine. The photometer and test sets for
this are described in the WTW catalog or on the Internet.
How to carry out the calibration is described in detail in the operating manual
of the measuring transmitter.
4.3
Chlorine measurement with the FCML 412
The FCML 412 chlorine sensor measures inorganic chlorine compounds
dissolved in water. The measured values determined with the photometer
according to the DPD-1 method (free chlorine) are directly comparable to the
values determined by the sensor.
).
FCML 412 N(-S), FCML 412-M12
ba77197e02
01/2024
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