5.5.2
P(ID) controller
The Liquisys M supports the definition of various controller functions. On the basis of the PID
controller, P, PI, PD and PID controllers can be implemented. To obtain the best control
response, use the controller best suited to the application in question.
•
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 expec-
ted.
•
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 con-
troller is inadequate.
Start-up
If there is no previous experience for the control parameter settings, use the values which
guarantee maximum control loop stability (see table). For optimisation, reduce the control gain K
p
until the control variable overshoots slightly.Then increase K
p
and reduce T
n
(shorter times) to
obtain the shortest possible correction time without overshooting. Adjust T
v
in the case of fast
correction times.
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
=
=
max. 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 R232,
MAX, MIN = upper and lower range values.
Recommendable settings for all types
Controller
behaviour
K
p
T
v
[min]
T
n
[min]
P
1·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
v
= 0:
D component not calculated
T
n
= 0:
I component not calculated
X
T
x
t
g
max
= ∆
∆
K
V
X
T
h
u
=
⋅
max
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
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 component
D component
e
setpo
cur
r
entval
ue
M A X M IN
* =
-
-
i
nt
OM253D5B.CHP
Liquisys M COM 223 / 253
Instrument configuration
Hauser
37
