Notes on Controller Settings
IP244
C79000–B8576–C860–02
4–134
4.4 Selecting the Controller Structure for a Given System
The controlled systems are particularly important for selecting the control loop elements. Their
characteristics are determined by the process control applications and cannot be changed
afterwards. An optimum control action can only be achieved by selecting a suitable controller,
whose action can be matched to the system data within certain limits.
Selection of suitable controller structures
Unsuitable
Unsuitable
T
v
T
u
<0.1
Suitable if no
significant delay
time
Slightly
worse
than PID
Worse
than PID
Control
with
delay time
Hardly required
for these
controlled
variables
Possible, but
I controller
alone usually
better
The most suitable controller types
for more sophisticated requirements
(apart from specially adapted
controllers)
Useless
Less suitable,
since required X
p
band usually too
great
No steady state deviationSteady state deviation
For limited
requirements and
P systems where
Suitable The most suitable controller types
for more sophisticated requirements
(apart from specially adapted
controllers)
System
PID PI PD P
Controller structure
Useless
Control +
disturbance
UselessPure
dead time
Control +
disturbance
UselessUseless
Dead time
+ 1st order
delay
Poor
Unsuitable
Dead time
+ 2nd order
delay
DisturbanceControl
Disturbance
with delay
time
1st order
+ very small
dead time
(delay)
Slightly
worse
than PID
Unsuitable UnsuitableHigher
order
Control
(without
delay)
Disturbance
(without
delay)
Control Disturbance
Not selfĆ
regulating
with delay
PID PI PD P
Controlled
variable
:
Temperature
Pressure
Flow
Suitable controllers for the most important controlled systems
Control +
disturbance
Control +
disturbance
Controller:
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