ABB i-bus KNX Product Manual page 39

5.5 T emperature control
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5.5.1 I ntroduction
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If the RTF/A 1.1 is not configured as a switching controller, it can be parameterised
either as a P or as a PI controller, whereby PI regulation is preferable.
With the proportional controller (P controller), the control value is modified statically
to the control deviation.
The proportional/integral controller (PI controller) is much more flexible, i.e. it controls
dynamically (faster and more accurately).
To explain the functioning of both temperature controllers, the room being heated is
compared to a container in the following example
The fill level of the container represents the room temperature.
The water supply represents the radiator output.
The heat losses of the room are represented by a tap.
In our example, the maximum supply quantity is assumed to be 4 litres per minute
and also represents the maximum heating output of the radiator in our example.
This maximum output is reached at a control value of 100%.
Accordingly, with a control value of 50% only half the water volume, i.e. 2 litres per
minute, flows into our container.
The strip width is 4l.
This means that the controller will regulate at 100%, as long as the actual value will
be less than or equal to (21l – 4l) = 17l.
Problem definition:
•
Required filling quantity:
21 litres (= set value)
•
At what point is the supply to be gradually reduced to avoid an overflow?
4l under the required fill quantity, i.e. at 21l - 4l = 17l (= strip width)
•
Outlet filling quantity
15l (=actual value)
•
The losses are 1l/minute
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