English (GB)
31
Fig. 39
Integral action
Differential action, PID action
With a differential action (D) controller, a deviation
initially generates a very high manipulated variable
which rapidly decays. In theory, the step-forced
response is an infinitely high "needle function" since
it only reacts to a change in the deviation.
In reality,
the magnitude of the deflection depends on the
magnitude of the change in deviation. The D
controller is only used together with P and I
controllers e.g. as a PD or PID controller.
The advantage is that fast adjustments are possible
as the controlled variable changes rapidly e.g. in the
case of faults. The characteristic of the D controller
is the derivative action time T
v
.
Fig. 40
Differential action
15.1.5 Adaptation and error correction
When adapting the controller to the controlled
system, use the basic parameter settings gained
from experience and the response of the controlled
variable which you observed when starting up the
control loop.
•
The controlled variable rapidly reaches the
setpoint without overshoots:
– In this case the controller is optimally set.
Fig. 41
Optimally set controller
•
The controlled variable oscillates around the
setpoint:
– The reset time T
n
is too small.
TM
03 70
95 161
3
t
0
I
max.
t
0
PI
T
n
P
I
max.
t
t
Manipulated variable
Manipulated variable
Time
Time
action
action
T
M
03
70
96
16
13
TM
03 70
97 161
3
t
0
T
n
P
I
D
max.
T
v
/4
PID
t
0
D
t
t
Manipulated variable
Manipulated variable
Time
Time
action
action
action
t
SP
Manipulated variable
Time
