Chapter 7 Usage of Various Functions
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2) Specification
(1) Control operation
a) Proportional operation (P operation)
(a) P action means a control action that obtain a manipulate value which is proportional to the deviation (E : the
difference between SV and PV)
(b) The deviation (E) is obtained by multiplying a reference value to the actual difference between SV and PV. It
prevents the deviation from a sudden change or alteration caused by external disturbance. The formula of
deviation is as following;
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PVSVbKpMV −××=
Kp : the proportional constant (gain)
b: reference value
SV: set value
PV: present value
(c) When E happens, MV by P operation is like <Fig 2-1>
<Fig 2-1> MV by P operation
(d) If the Kp is too large, the PV reaches to the SV swiftly, but it may causes a bad effect like oscillations shown in
the Fig. 2.2.
(e) 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. 2.3.
(f) 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.
(g) 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
Time
Time
E
Kp ⋅ E
E
SV
MV
SV
Kp ⋅ E
E
MV
PV
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