Chapter 6 Usage of Various Functions
6-8
(b) Integral Operation (I Operation)
①
With integral operation, the manipulate value (MV) is increased or decreased
continuously in accordance time in order to eliminate the deviation between the SV
and PV. When the deviation is very small, the proportional operation can not produce
a proper manipulate value and an offset remains between PV and SV. The integral
operation can eliminate the offset value even the deviation is very small.
The period of the time from when the deviation has occurred in I action to when the
MV of I action become that of P action is called Integration time and represented as
Ti.
②
Integral action when a constant deviation has occurred is shown as the following Fig.
7.3.
As shown in the expression, Integral action can be made stronger or weaker by
adjusting integration time (Ti) in I action. That is, the more the integration time (the
longer the integration time) as shown in Fig. 7.4, the less 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. 7.5, 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.
③
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. 7.3 The integral action with constant deviation
∫
=
Edt
Ti
Kp
MV
