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;
[]
)()()( nPVnSVKnP −=
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
dsse
T
K
tI 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( ne
Ti
K
h
nInI =
−+ where, h : sampling period
)()()1( ne
Ti
Kh
nInI +=+
(c) D control
The continuous formula of derivative term is as following;
dt
dy
KTdDD
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