LSIS Master-K K1000S - Control Actions; Proportional Operation (P Operation)

Chapter 15 The PID function of K200S MASTER-K
15-2
15.2 Control actions
15.2.1 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 multiplying a reference value to the actual difference
between SV and PV. It prevents the deviation value from a sudden change or alteration
caused by external disturbance. The formula of deviation is as following;
[
]
PVSVbKpMV −××=
Kp : proportional constant (gain)
b : reference value
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 shown in the Fig. 15.2
4) 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. 15.3
5) The manipulation value (MV) varies from 0 to 40,000. User can define the maximum
value of MV (MV_MAX) and the minimum value (MV_MIN) within the range 0 ~ 40,000.
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’, and user can define the bias value in
sequence program.
Fig. 15.1 The block diagram of PID control system
PID
operation
D/A conversion
and hold circuit
Process
(Actuator, sensor)
A/D conversion
Deviation
Set
value
Present
value
+
–