Commissioning
21
© Lutz-Jesco GmbH 2020
Subject to technical changes.
200123
BA-46020-02-V04
Multi-Channel Controller
TOPAX
®
MC
Operating instructions
8.2.1.4 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 con-
troller 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.
8.2.1.5 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 con-
troller 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 ac-
tors.
Difference
You can calculate the difference between two measured values or the dif-
ference between a measured value and a fixed reference value.
Perform the following work steps:
1.
Working in the main menu under System > Inputs, navigate to the
“Virtual” tab.
2.
State the following information.
3. Calculation:
Select “difference”.
4.
Select a sensor.
5.
Select a second sensor or a reference value. The second sensor must
output the same measured value as the first. You will need to enter
the reference value manually.
6. Min-alarm:
Activate or deactivate the minimum alarm and state a
difference value under which the alarm will be triggered.
7. Max-alarm:
Activate or deactivate the maximum alarm and state a
difference value over which the alarm will be triggered.
8. Delay:
Set a time delay for the minimum and maximum alarm.
ü
Configuration of the difference completed.
Combined chlorine
Bound chlorine is calculated from the difference between the total chlo-
rine and the free chlorine:
Bound chlorine = total chlorine – free chlorine
At least one total chlorine measurement is required to calculate bound
chlorine. The chlorine value can be entered manually as a single refer-
ence value or a corresponding sensor input is selected.
Perform the following work steps:
1.
Working in the main menu under System > Inputs, navigate to the
“Virtual” tab.
2.
Working in the “Virtual” tab, configure the desired calculation of the
bound chlorine and state the following information.
3. Calculation:
Select “bound chlorine” to calculate the bound chlorine.
4. Total chlorine:
Select the sensor which measures the total chlorine.
5. Free chlorine:
Select the sensor which measures the free chlorine. If
no sensor is present, you can enter a reference value measured once
which can be used for the calculation.
6. Min-alarm:
Activate or deactivate the minimum alarm and state a
value under which the alarm will be triggered.
7. Max-alarm:
Activate or deactivate the maximum alarm and state a
value over which the alarm will be triggered.
8. Delay:
Set a time delay for the minimum and maximum alarm.
ü
Configuration of the bound chlorine completed.
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. 20 “Dissociation curve of the effective chlorine” on page 22) of
the chlorine.
The actual disinfectant effect of the chlorine is generated by the hy-
pochlorous 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 chlo-
rine content than is actually in the process water. For high pH-values sig-
nificant differences will therefore occur between the expected and actual
disinfection if assessed by photometric analysis. The calculation of the ef-
fective chlorine can be used to display the proportion of the hypochlorous
acid (HCIO), i.e. the proportion which contributes to the disinfectant effect.
