Chapter 2. SPECIFICATIONS
2 - 5
2.4.2 Control Action
1) Proportional Action (P Action)
(1)
P action means a control action that obtains a MV which is proportional to the deviation (E: the difference
between SV and PV).
(2)
The expression which denotes the change relationship of E to MV in P action is shown as follows:
where Kp is a proportional constant and means gain.
(3)
When deviation occurs, the MV by P action is shown in Fig. 2.1.
[Fig. 2.1] MV with the proportional action
(4)
As shown in Fig. 2.1, the larger the proportional constant Kp the larger the MV, that is, the stronger the P
action when the deviation(E) is same . Also, the smaller the Kp the smaller the MV after P action.
(5)
If the Kp is too large, PV reaches SV swiftly but can make bad effects like oscillations shown in Fig. 2.2
and cause damage in control stability.
(6)
If the Kp is too small, oscillations do not occur but the velocity with which PV reaches SV slows down and
offset can happen as shown in Fig. 2.3.
(7)
Manipulated Value varies within 0 to 16,000.
MV = Kp
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