NB!
If the frequency converter is running a the
current limit before the required start fre-
quency is obtained, the process regulator
will not be activated. For the regulator to
be activated anyway, the start frequency
must be lower to the required output fre-
quency. This can be done during opera-
tion.
PID start frequency may not be set higher
than f
MIN
if using pipe fill mode.
440
Proces PID proportioanl gain
(PROC. PROP. GAIN)
Value:
0.0 - 10.00
0.01
Function:
The proportional gain indicates the number of times
the deviation between the setpoint and the feedback
signal is to be applied.
Description of choice:
Quick regulation is obtained by a high gain, but if the
gain is too high, the process may become unstable due
to overshoot.
441
Process PID integration time
(PROC. INTEGR. T.)
Value:
0.01 - 9999.99 (OFF)
OFF
Function:
The integrator provides an increasing gain at a con-
stant error between the reference/setpoint and the
feedback signal. The greater the error, the quicker the
integrator frequency contribution will increase.The in-
tegral time is the time needed by the integrator to make
the same change as the proportional gain.
Description of choice:
Quick regulation is obtained at a short integral time.
However, this time may become too short, which can
make the process unstable due to overswing. If the in-
tegral time is long, major deviations from the required
setpoint may occur, since the process regulator will
take a long time to regulate in relation to a given error.
442
Process PID differentiation time
(PROC. DIFF. time)
Value:
0.00 (OFF) - 10.00 sec.
0.00 sec.
Function:
The differentiator does not react to a constant error. It
only makes a gain when an error changes. The quicker
the deviation changes, the stronger the gain from the
differentiator. The gain is proportional to the speed at
which the deviation changes.
Description of choice:
Quick regulation is obtained with a long differentiation
time. However, this time may become too long, which
can make the process unstable due to overswing.
443
Process PID diff. gain limit
(PROC. DIFF.GAIN)
Value:
5.0 - 50.0
5.0
Function:
It is possible to set a limit for the differentiator gain. The
differentiator gain will increase if there are fast
changes, which is why it can be beneficial to limit this
gain. Thereby a pure differentiator gain is obtained at
slow changes and a constant differentiator gain where
quick changes to the deviation occur.
Description of choice:
Select a differentiator gain limit as required.
444
Process PID lowpass filter time
(proc filter time)
Value:
0.02 - 10.00
0.02
Function:
Noise in the feedback signal is dampened by a first
order lowpass filter to reduce the noise's impact on the
process regulation. This can be an advantage e.g. if
there is a lot of noise on the signal.
Description of choice:
Select the required time constant (t). If a time constant
(t) of 0.1 s is programmed, the cut-off frequency for the
lowpass filter will be 1/0.1 = 10 RAD/sec., correspond-
ing to (10 / 2 x
π
) = 1.6 Hz. The process regulator will
thus only regulate a feedback signal that varies by a
frequency lower than 1.6 Hz. If the feedback signal
= factory setting, () = display text, [] = value for use in communication via serial communication port
MG.27.E2.02 - VLT is a registered Danfoss trademark
103
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