Chapter 7 Usage of Various Functions
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(b) Integral action when a constant deviation has occurred is shown as the following Fig. 2.4.
Fig. 2.4 The integral action with constant deviation
(c) The expression of I action is as following;
As shown in the expression, Integral action can be made stronger or weaker by adjusting integration time (Ki)
in I action.
That is, the more the integration time (the longer the integration time) as shown in Fig. 2.5, the lesser the
quantity added to or subtracted from the MV and the longer the time needed for the PV to reach the SV.
As shown in Fig. 2.6, when the integration time given is short the PV will approach the SV in short time since
the quantity added or subtracted become increased. But, If the integration time is too short then oscillations
occur, therefore, the proper P and I value is requested.
(d) Integral action is used in either PI action in which P action combines with I action or PID action in which P and
D actions combine with I action.
Fig. 2.5 The system response when a long integration time given
∫
= Edt
Ti
Kp
MV
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