Chapter 3: Configuration 3.6 Setting the Configuration
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pPi Controller
The pPi (predicting PI) controller is a specially designed dead time controller. It
should be used when the dead time is longer than twice the dominant process time
constant. If the dead time is varying, for example with flow or conveyor speed,
the pPI controller can be combined with gain scheduling. The Autotuner function
is not needed and is automatically disconnected when pPI control is configured.
The pPI controller is easy to tune, first by making a step response test on the
process and then setting the controller parameters by observation. Thereafter the
pPI controller can be adjusted manually. In most cases an increase in K (Gain) or
a decrease in TI (Integral Time) gives faster control but poorer damping.
In the figure below:
∆ y = y1 – y0
∆ u = u1– u0
T = t2 – t1
L = t1 – t0
Figure 51 Dead Time Process Step Response.
t0 t1 t2
u0
y0
u1
y1
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