Setting Parameters
01/02 AWB8230-1415GB
136
Setting the PID parameters
Values for the PID parameters must be chosen depending on the
application and the system’s control characteristics. The following
points are important to achieve effective PID control:
• A stable steady-state behaviour
• A fast response
• A small system deviation in the steady state
Parameters K
p
, T
i
and K
d
must be set within the stable operating
range. As a general rule, increasing one of the parameters K
p
, K
i
(= reduction of T
i
) and K
d
results in a faster system response. A
very large increase however, causes system instability, as the
returned actual value will begin to oscillate, in the worst case,
resulting in divergent behaviour (
a
Fig. 136 to Fig. 139):
The following table provides guidelines for setting each para-
meter.
Table 21:
Setting the controller regulation times
Figure 136: Divergent behaviour
w: Setpoint value
a
Output signal
Figure 137: Oscillation, dampened
w: Setpoint value
a
Output signal
w
t
a
w
t
a
Figure 138: Good control characteristics
w: Setpoint value
a
Output signal
Figure 139: Slow control, large static system deviation
w: Setpoint value
a
Output signal
A setpoint
change
causes a slow response
Increase proportional
component (K
p
)
causes a fast but unstable
reaction
Set a lower P compo-
nent
Setpoint and
actual value
differ greatly
Reduce integral
component (T
i
)
approach each other after
oscillation
Set a higher I compo-
nent
After increa-
sing K
p
the response is still slow
Increase D component
(K
d
)
the response is still
unstable
Set a lower D compo-
nent
w
t
a
w
t
a
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