Rockwell Automation 1771-PD PID MODULE (+DU) - Manual (Page 8)

Introduction
Chapter 1
1Ć5
Figure 1.1
Simplified PID Algorithm
SP
Process
A/D
Hardware
/
Digital
PV
+
S P
I
D
V
BIAS
Lead
Feedforward Input
(FFV)
D/A
Hardware
11099
Variable
Analog
Input
Filter
-
Lag
Analog
Output
S S
/
SP
PV
+
S
Error=SP-PV -
V
P
+ V
I
+ V
D
BIAS
+
S
+
V = V
P
+ V
I
+ V
D +
BIAS
P
r
o
c
e
s
s PV = Process Variable
SP = Set Point
V = Control Variable
V
P
= Proportional Term K
P
V
I
= Integral Term K
I
V
D
= Derivative term K
D
Control Variable
Controller Gain K
C
Reset Term 1/
Ti
Rate Term T
d
AĆB ISA
Error=SP-PV
a) PID Closed Loop Control
b) Major Control Functions
Control Variable
V
PID