Instruction manual

Cascade Controller Option
■ Optimization of the process regulator
Quick Menu 043 Par. 423 PID proportional gain
(PID PROP. GAIN)
Value:
0.00 - 10.00
✭ 0.30
Function:
Determines how fast the system responds to
a change in feedback.
Description of choice:
Quick regulation is obtained by a high gain, but
if the gain is too high, the process may become
unstable. See Optimization of the Process Regulator
for information on proper adjustment.
Quick Menu 044 Par. 424 PID integration time
(PID INTEG R.TIME)
Value:
0.01 - 9999.00 sec. (OFF)
✭ OFF
Function:
The integrator adds the error signal over time and uses
this to correct the speed of the drive. The integration
time is the time needed by the integrator to have
the same effect as the proportional gain.
Description of choice:
Fast regulation is obtained by setting a short
integration time. However, if this time is too short,
the process will overcorrect and become unstable.
See Optimization of the Process Regulator for
information on proper adjustment.
P
rocedure for Optimization of the Process Regulator
The process regulator is set by Quick Menu items
43 and 44 (parameters 423 and 424). To optimize
the proportional gain and integration time, in most
processes, this can be done as follows:
1. Start the motor.
2. Set parameter 423, PID Proportional Gain,to0.3
and increase it until the feedback signal becomes
unstable. Then reduce the value until the feedback
signal has stabilized. Now lower the proportional
gain by about half (40% to 60%).
3. Set parameter 424, PID Integration Time,to20
seconds and reduce the value until the feedback
signal becomes unstable. Increase the integration
time until the feedback signal stabilizes. Now
increase the integration time from 15% to 50%.
Starting and stopping the drive will produce the
necessary error signal in the process to set the PID.
PID equation:
The AFD PID controller operates in accordance
to the following equation:
PID out = P[e(t) + 1/ l f e(t) dt] + D e(t)/dt
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