Regulator behaviour All three fractions (P-fraction, I-fraction, D-fraction) are added together and
act as an adjustment to the compound regulator's load specification. The
value is added to the momentary internal load.
As long as the actual value is below the set-point, the P-fraction and the
I-fraction are positive, i.e. both these fractions act to increase the load
specification.
Only the D-fraction is still negative in such a case (assuming the boiler's
temperature is rising).
A sufficiently large D-factor should be selected, in order to avoid an
excessively large overshoot during burner startup.
The D-fraction can also be increased by increasing the readjustment
interval, since the boiler has more time for a change in temperature.
If, despite a large set-point deviation, the burner is not driven to full load or
base load respectively, the P-factor should be increased.
The larger the readjustment interval, the quieter the compound but also the
larger the actual value's deviation from the set-point and the slower the
adjustment.
The overshoot effect can result in a failure of the control mechanism, hence
the readjustment interval should be so selected that the compound
(the internal load) settles down.
Examples Parameter Name Hot water Steam
805 120 280 600
806 60 360 300
807 20 50 35
808 integral 15 2 20
implicitly optimisation is provided by customer
P-factor
I-factor
D-factor
time
Output regulator Setting the regulator
38
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