ABB i-bus KNX Product Manual page 41

P controller as temperature controller
The P controller behaves in exactly the same way with a heating control as in the
previous example.
The set temperature (21°C) can never be fully reached.
The remaining control deviation becomes higher the greater the heat losses, i.e. the
lower the outside temperatures fall.
5.5.3 B ehaviour of the PI controller
4 9 B
Unlike the pure P controller, the PI controller works dynamically.
With this type of controller, the set value does not remain unchanged even with a
constant deviation.
In the first moment, the PI controller sends the same control value as the P controller,
but this is increased even more the longer the set value is not reached.
This increase is carried out in a time-controlled way via what is known as the
integration time.
With this calculation process, the control value is only then no longer changed if the
set value and the actual value are the same.
This produces a balance between the supply and run-off in our example.
Note on temperature control:
Good control depends on the balancing of the strip width and integration time with
the room which is to be heated.
The strip width affects the increment of the control value change:
Large strip width = finer increments with a change in control value.
The integration time affects the reaction time to temperature changes
Long integration time = slow reaction.
A poor balance can mean that either the control value is exceeded (overshoots), or
the controller takes too long to reach the set value.
Normally, the best results are achieved using the via system type setting.
Parameter page
Control system
Parameters
Setting the control parameters
Setting
via system type
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