Chapter 6 Usage of Various Functions
6-7
2) Specification
(a) Proportional Operation (P operation)
① P action means a control action that obtains 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;
]
PVSVKpMV
where,
Kp: the proportional constant (gain),
SV: set value,
PV: present value
③ If the Kp is too large, the PV reaches to the SV swiftly, but it may cause a bad effect
like oscillations.
④ If the Kp is too small, oscillation will not occur. However, the PV reaches the SV
slowly and an offset may appear between PV and SV as shown in the Fig. 7.2.
⑤ 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.
⑥ 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.
Fig 7.1 MV by P operation
Fig. 7.2 The relation between Proportional constant (Kp) and present value (PV)
EKMV
P
Time
Deviation(E)
Manipulate value (MV)
: Kp is too small
Time
PV
SV
Oscillation
Offset
: Kp is too large
: Deviation
: Manipulating value
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