LG MASTER-K 120S Series, Руководство пользователя, Страница: 109 / 306

Chapter 7 Usage of Various Functions
7-25
(2) Realization of PID control on the PLC
In this chapter, it will described that how to get the digitized formula of the P, I, and D terms.
(a) P control
The digitized formula of P control is as following;
[ ]
) ( ) ( ) ( n PV n SV K n P
− =
n : sampling number K : proportional gain constant
b : reference value SV : set value PV : present value
(b) I control
The continuous formula of I control is as following;
∫
=
t
i
ds s e
T
K
t I
0
) ( ) (
: integral term
K : proportional gain constant Ti : integral time
e(s) : deviation value
By derivation about t, we can obtain;
e
Ti
K
dt
dI
=
where, e = (SV – PV) : deviation value
The digitized formula is as following;
) (
) ( ) 1 (
n e
Ti
K
h
n I n I
=
− +
where, h : sampling period
) ( ) ( ) 1 ( n e
Ti
Kh
n I n I
+ = +
(c) D control
The continuous formula of derivative term is as following;
dt
dy
KTd D D
dt
d
N
Td
− = + ×
N : high frequency noise depression ration
y : the object to be controlled (PV)
(3) Instruction and parameter setting
For the PID operation of MASTER-K120S, following 2 instruction are included in the KGLWIN software.
No. Name Description
1 PID8 Perform the PID operation
2 PID8AT Perform the auto tuning operation