LG Electronics 120S user manual Kp is too large

Chapter 7 Usage of Various Functions

2)Specification

(1)Control operation

(a)Proportional operation (P operation)

① P action means a control action that obtain a manipulate value which is proportional to the deviation (E : the difference between SV and PV)

②The deviation (E) is obtained by difference between SV and PV and the formula of deviation is as following;

MV = Kp ⋅ [SV − PV ] where, Kp : the proportional constant (gain), SV: set value, PV: present value

③When E happens, MV by P operation is like Fig.7.1

	: Deviation
	: Manipulating value
Deviation(E)	Manipulate value (MV)
	Time

Fig 7.1 MV by P operation

④If the Kp is too large, the PV reaches to the SV swiftly, but it may causes a bad effect like oscillations.

⑤If the Kp is too small, oscillation will not occur. However, the PV reaches to the SV slowly and an offset may

appear between PV and SV shown in the Fig. 7.2.

⑥The manipulation value (MV) varies from 0 to 4,000. User can define the maximum value of MV (MV_MAX) and

minimum value (MV_MIN) within the range 0 ~ 4,000.

⑦When an offset remains after the system is stabilized, the PV can be reached to the SV by adding a certain value. This value is called as bias value, and user can define the bias value

		: Kp is too large
PV	Oscillation	: Kp is too small
SV
		Offset
		Time

Fig. 7.2 The relation between Proportional constant (Kp) and prosent value (PV)

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