Commissioning of the water sampling station
26
© Lutz-Jesco GmbH 2020
BA-42840-02-V03
Water sampling station
EASYPRO COMPACT
Operating instructions
8.6.1.3 Compensation of cross sensitivities
The water parameters which you measure with the device can be falsified
by interference (e. g. with temperature or pH value).
The device can compensate these interferences automatically.
Perform the following work steps:
1.
Working in the main menu under System > Inputs, navigate to the
“Compensation” tab.
2.
Working in the “Compensation” tab, configure every sensor
connected for which the measured value is to be compensated and
state the following information
3. Temperature:
If it is possible to compensate for the influence of the
temperature, you can select a fixed reference value or one of the four
temperature inputs.
4. pH value:
If it is possible to compensate for the pH value error, you
can select a fixed reference value or a sensor input.
ü
Configuration of the compensation completed.
8.6.1.4 Disturbance variable
You can connect the measurement of a disturbance variable (e.g. a flow
volume) to an analogue 4 − 20 mA input. The disturbance variable can
then be taken into account with a factor (0.1 to 10) during the calculation
of the control variable Y. The control variable Y will be multiplied with the
disturbance variable during the calculation.
Example:
If the factor = 2 and the disturbance variable amounts to 42 %,
the controller can be set to a maximum of the control variable Y = 84 %. If
the factor = 0.5 and the disturbance variable amounts to 42 %, the
controller can be set to a maximum of the control variable Y = 21 %.
Perform the following work steps:
1.
Working in the main menu under System > Controller, navigate to the
“Disturbance variable” tab and state the following information.
2. Disturbance variable:
Set the disturbance variable to an input signal
of 4 – 20 mA or 0 – 20 mA. You can also deactivate the disturbance
variable.
3. Unit:
As a rule, the disturbance variable is the measurement of a flow.
Select the desired unit.
ü
Configuration of the disturbance variable input completed.
8.6.1.5 Virtual inputs
You can calculate a new value from multiple measurements or reference
values using a virtual input. You can assign the new virtual value to a
controller in the configuration assistant.
In this way, you can calculate the difference between the bound chlorine
and the effective chlorine and use it as the basis for controlling your
actors.
Effective chlorine
The disinfectant effect of the free chlorine is highly dependant on the pH
value of the process water. The pH value influences the reactivity of the
Chlorine ions. This relationship is underscored by the dissociation curve
(Fig. 23 “Dissociation curve of the effective chlorine” on page 26) of the
chlorine.
The actual disinfectant effect of the chlorine is generated by the
hypochlorous acid (HClO). The figure shows that the proportion of the
HClO is largest between pH 2 and pH 7.5. The disinfectant effect is very
low outside this 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 process water. For high pH-values
significant differences will therefore occur between the expected and
actual disinfection if assessed by photometric analysis. The calculation of
the effective chlorine can be used to display the proportion of the
hypochlorous acid (HCIO), i.e. the proportion which contributes to the
disinfectant effect.
100 %
50
10
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0,5
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pH > 1,7 : Cl2
+
H2O � HCIO
+
HCI
pH > 7,5 : HCIO � H
+
+
CIO-
14
(pH)
Fig. 23: Dissociation curve of the effective chlorine
