LS Industrial Systems GLOFA G7M-DR20U, User Manual

Page: 132 / 367

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;
Kp : proportional gain constant, SV: set value, PV: present value
(b) I control
The continuous formula of I control is as following;
Kp : proportional gain constant Ti : integral time
E(s): deviation value
By derivation about t, we can obtain;
where, e = (SV – PV): deviation value
The digitized formula is as following;
where, h: sampling period
(c) D control
The continuous formula of derivative term is as following;
N: high frequency noise depression ratio
y: the object to be controlled (PV)
) ( ) ( PV SV K n P
P
− =
∫
=
t
i
P
ds s E
T
K
t I
0
) ( ) (
E
T
K
dt
dI
i
P
=
) (
) ( ) 1 (
n E
T
K
h
n I n I
i
P
=
− +
) ( ) ( ) 1 ( n E
T
h K
n I n I
i
P
+ = +
dt
dy
T K n D
dt
n dD
N
T
d P
D
− = +
) (
) (