Multiplicative Interference Variable - ProMinent DULCOMETER diaLog DACb Assembly And Operating Instructions Manual

[Control]
Setting the
Applicational example of additive
interference variable
Applicational example:
13.10.2

Multiplicative interference variable

126
mA input, channel 3: mA interference variable
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Correction functions included:
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– pH compensation for chlorine
– Additive interference variable for channel 2
– Temperature for pH
If the addition of a chemical is largely dependent on the flow (pro‐
portional dependency), then the addition of an additive interference
variable proportional to the interference variable (flow), adds a pro‐
portion of the control variable to the control variable of the setpoint
controller (setpoint control, that is the comparison, setpoint: actual
value). It is also possible to completely switch off control of the set‐
point and only provide flow-proportional metering. The measure‐
ment of the main measured value can be used together with the
limit values as a monitoring function.
You are to chlorinate potable water. The required setpoint is 0.3
mg/l (ppm) chlorine. The volumetric flow of the drinking water is
measured with a flow meter. The measuring signal of the flow
meter is routed to the controller via a 4 ... 20 mA signal. A chlorine
sensor CLE3 continuously measures the chlorine. The volumetric
flow changes within a wide flow range from 0 ... 250 m³/h. The
chlorine concentration of 0.3 mg/l is achieved using the proportion‐
ality between the water flow and the added volume of chlorine.
This requires the correct design of the metering pump according to
the chlorine concentration. If the chlorine requirement were now to
increase, caused by a higher flow or greater depletion (higher tem‐
perature, more germs), then an additional positive fraction of the
setpoint control would be added to the flow-proportional control
variable. If, by contrast, too much chlorine is metered, caused by a
too high proportionality, then a negative control variable would be
issued and added to the flow-proportional control variable, and the
resulting control variable would fall.
Set the following in the menu of the control:
[Menu] , [Control] , [Interference variable] , [On] , [Signal source] =
[mA input 2]
[Effect] : [additive]
[Assignment] : [0...20mA] or [4...20 mA]
[Nominal value] : enter the maximum expected analogue current
here, e.g. 18 mA
The multiplicative interference variable can influence the control
variable of the setpoint controller over the entire control range pro‐
portionally to the interference variable. This corresponds to a pro‐
portionality factor of 0.00 = 0 % and 1.00 = 100 %, including all
intermediate values.