Jesco EASYPOOL SMART 02, Operating Manual

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EASYPOOL SMART 0 Operating Manual | 19
Controller
Fig. 4.5.1: Chlorine dissociation curve as a function of the pH value
For photometric measurements the pH value of the sample is
buffered to approx. pH 6.5. As a result the measurement has a
higher effective chlorine content than is actually in the bathing
water. In the presence of high pH-values significant differences
will occur between expected and actual disinfection if assessed
by photometric analysis. The main display will show therefore
free chlorine values: the photometry value and the the effec-
tive chlorine content ("eff. chlor") to kill germs at the current pH
value.
NOTICE!
For saline bathing water use a platinum/silver chlorine
measurement cell instead of platinum/copper.
Calibration
Before starting the calibration, the upper value of the measuring
range of the sensor must be specified (Main menu >> Menu
>>Service >> Inputs). In non-DIN 19643 operated swimming
pools it is preferable to use the 0 … mg/l measuring range.
The input can then be calibrated using a two-point calibration
(Main menu >> Calibrate >> Free Chlorine >> point):
The physical value (µA) measured at the sensor is shown on the
display during calibration.
Calibration method 1: Zero-point calibration
The sample water flow is therefore stopped. (ball valve on water
sampling station inlet). The value of the physical quantity shown
on the display (approx 5 … 10 μA) can be saved with "OK" as
soon as it stops changing. The device automatically changes to
the next menu section.
Calibration method 2: DPD
The sensor is operated with sample water. If the physical value
on the display does not change any more, the chlorine content in
the sample water is determined via a photometer (DTP method).
To avoid signal deviations during DTP determination as reading
errors, the sample water must be taken from the measuring cell
and the current signal at the time of removal of the sample water
must be saved. The content of chlorine in water is measured by
means of the DPD method. The value must be set in the control-
ler and saved by pressing OK.
After storage the transconductance value of the chlorine sensor
is shown. The typical transconductance reading is 5 µA … 35
µA (depending on water sample) per mg/l of free chlorine. The
accuracy of resistivity measurements is monitored throughout
the process.
1-point calibration is often sufficient (reference value only) to
check the chlorine content after optimization.
4.5.2 Measuring input pH value
The voltage signal transmitted by the combination electrode is
proportional to the pH value. This voltage is defined by the Nernst
voltage. The Nernst voltage ist he change in voltage per pH unit.
It depends on the temperature of the medium to be measured
(see corresponding technical literature or German Standard DIN
1961).
The Nernst voltage is measured between the pH glass electrode
and a reference electrode. Mechanically these two electrodes are
integrated in a pH combination electrode.
Calibration
Calibration of the electrode may be performed by ways of "-
point calibration" with buffer solutions or by "1-point calibra-
tion" with final input of the resistivity value. "Single point calibra-
tion" requires the transconductance of the single-rod measuring
cell to be measured in a laboratory beforehand.
The actual voltage of the single-rod measuring cell and the
theoretical value (ideal value) of the buffer solution setting are
displayed during calibration. This allows the rating of the single-
rod measuring cell to be determined during calibration, assuming
fresh buffer solutions.
The reaction time for any brand new electrode is just a few sec-
onds and the electrode is considered as fully adjusted when the
physical reading becomes stable. In the case of older combina-
tion electrodes the reaction time may be longer.
2-point calibration
Main menu >> Calibrate >> pH value >> point
Buffer 1: Zero-point calibration
Submerge the pH combination electrode in a buffer solution
which is equivalent or close to the zero point of the electrode.
The ideal zero point (O mV) of the combination electrode is pH
7.00, the actual zero point, however, deviates slightly from this
value. For zero-point calibration a buffer solution of pH 6.80 is
available from the manufacturer. When immersing the pH single-
rod measuring cell in this solution, a voltage of 1 mV can be
displayed theoretically. The physical value actually measured is,
however, always different from the theroretical one.
When the physical value on the display becomes stable, you may
save the calibrated value by pressing „OK“.
IMPORTANT!
Should the actual measured voltage strongly differ
from the design zero-point of the electrode, it means
there is a zero-point drift of the electrode. Zero-point
drift should not exceed the specifications of the DIN
Standards 19265. In the event of zero-point drift
exceeding ± 40 mV, TOPAX DX gives a poor probe
calibration warning.