P controller:
Used for simple linear control
purposes with small system deviations. Where
major changes are to be controlled,
overshooting may occur. A control offset is to
be expected.
PI controller:
Used for processes where
overshooting is to be avoided and permanent
offsets are not allowed.
PD controller:
Used for processes that
require quick response and where peaks are
to be corrected.
PID controller:
Used for processes for which
the type of control provided by a P, PI or PD
controller is inadequate.
Adjustments of P(ID) controller
Three parameters can be adjusted in the
case of a PID controller:
– the control gain K
p
(P influence)
– the integral action time T
n
(I influence)
– the derivative action time T
v
(D influence)
Step response of process
y
=
set value
y
h
=
control range
T
u
=
delay time [s]
T
g
=
recovery time [s]
V
max
=
=
maximum slew rate of
control variable [K/s]
X
max
=
maximum process value
X
h
=
controller adjustment range
Controller characteristics
,
where
set point = set point from R332.
Recommendable settings for all types
Contr. response
K
p
[%]
T
v
[s]
T
n
[s]
P
K
0
0*
PI
2.6 K
0
6 T
u
PD
0.5 K
T
u
0*
PID
1.7 K
2 T
u
2 T
u
* T
n
= 0:
component is not calculated
T
n
→ ∞
: calculated component
→
0
Start-up
If there is no previous experience for the
control parameter settings, values should be
used which guarantee maximum control loop
stability (see table).
For optimisation, the control gain K
p
is reduced
until the control variable overshoots slightly.
Then K
p
is increased somewhat, and the T
n
setting is reduced (shorter times) to obtain the
shortest possible correction time without
overshooting.
T
v
must also be adjusted in the case of fast
correction times.
REGEL01.CDR
100 %
On
0 %
Off
y
t
X
h
T
u
T
g
∆
x
∆
t
X
max
[%]
[°C]
y
h
Fig. 5.6
Control characteristic
X
T
x
t
g
max
= ∆
∆
K
V
X
T
h
u
=
⋅ ⋅
max
100 %
y
K
e
T
e
T e
e
p
n
i
i
v
l
l
l
l
=
⋅
+
⋅
+
−
L
NM
O
QP
∗
∗
∗
−
∗
∑
1
1
e
j
I comp.
D comp.
e
set point
actual value
set point
∗
−
=
Instrument configuration
Liquisys M CLM 223 / 253
32
Hauser
