α
2 Simple Application Controllers
Function Blocks 6
6 - 55
Table 6.25: PID Equations
Filtered Process Value
Filtered Set Value
Deflection (Error Value)
Integration Value
Derivative Value
C o n t r o l Va l u e C h a n g e i n
Forward Operation
C o n t r o l Va l u e C h a n g e i n
Reverse Operation
Manipulation Value
Table 6.26: List of Additional Variables used in the PID equations
Variable
Description
EV
n
Deflection for current sample
EV
n-1
Deflection of previous sample
I
n
Intergration Value for current sample
K
D
Derviative Gain
K
P
Proportional Gain
MV
n
Output Value for current sample (Manipulated Value)
PV
fn
Measured Value (filtered) for current sample
PV
fn-1
Measured Value (filtered) for previous sample
PV
fn-2
Measured Value (filtered) for two samples ago
PV
n
Measured Value for current sample
SV
fn
Set Value (filtered) for current sample
SV
fn-1
Set Value (filtered) for previous sample
SV
n
Set Value for current sample
SV
n-1
Set Value for previous sample
T
D
Dervative Time
(
)
n
fn
f
n
fn
PV
PV
PV
PV
−
+
=
−
1
á
(
)
(
)
1
1
1
−
−
+
−
+
+
=
fn
I
n
n
I
n
S
I
S
fn
SV
T
SV
SV
T
SV
T
T
T
SV
β
αβ
β
fn
fn
n
SV
PV
EV
−
=
n
I
S
n
EV
T
T
I
=
(
)
1
2
1
2
−
−
−
+
+
−
+
=
n
D
fn
fn
fn
D
D
S
D
n
D
K
PV
PV
PV
T
K
T
T
D
(
)
(
)
n
n
n
n
P
n
D
I
EV
EV
K
MV
+
+
−
=
∆
−
1
(
)
(
)
n
n
n
n
P
n
D
I
EV
EV
K
MV
+
+
−
−
=
∆
−
1
∑
∆
=
n
n
MV
MV
