LG Electronics 120S user manual Where, h sampling period, Perform the PID operation, PID8AT

Chapter 7 Usage of Various Functions

(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;

P(n) = K[SV (n) − PV (n)]

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;

I (t) = K ∫ t e(s)ds : integral term

Ti 0

K : proportional gain constant	Ti : integral time
e(s) : deviation value
By derivation about t, we can obtain;

dIdt = TiK e where, e = (SV – PV) : deviation value The digitized formula is as following;

I (n + 1) − I (n)	=		K	e(n) where, h : sampling period
h
			Ti
I (n + 1) = I (n) +		Kh			e(n)
			Ti

(c) D control

The continuous formula of derivative term is as following;

TdN ⋅ dtd D + D = −KTd dydt

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

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