LG MASTER-K 120S Series User Manual page 104

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)
② The deviation (E) is obtained by difference between SV and PV and the formula of deviation is as following;
=
MV
③ When E happens, MV by P operation is like Fig.7.1
④ If the Kp is too large, the PV reaches to the SV swiftly, but it may causes a bad effect like oscillations.
⑤ If 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.
⑥ The 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.
⑦ When 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
SV
[ ]
× −
where, Kp : the proportional constant (gain), SV: set value, PV: present value
Kp SV PV
Deviation(E)
PV
Fig. 7.2 The relation between Proportional constant (Kp) and prosent value (PV)
Manipulate value (MV)
Fig 7.1 MV by P operation
Oscillation
Offset
7-20
: Deviation
: Manipulating value
Time
: Kp is too large
: Kp is too small
Time