Danfoss VLT Decentral FCD 300 Operating Instructions Manual page 70

VLT® Decentral FCD
quency must be lower to the required output frequen-
cy. This can be done during operation.
440 Proces PID proportioanl gain
Value:
0.0 - 10.00
Function:
The proportional gain indicates the number of times the deviation be-
tween 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
Value:
0.01 - 9999.99 (OFF)
Function:
The integrator provides an increasing gain at a constant error between
the reference/setpoint and the feedback signal. The greater the error, the
quicker the integrator frequency contribution will increase.The integral
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 integral 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
Value:
0.00 (OFF) - 10.00 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
Value:
5.0 - 50.0
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 bene-
ficial 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
Value:
0.02 - 10.00
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:
0.01
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., corresponding to (10 / 2 x π) = 1.6 Hz. The process regu-
lator will thus only regulate a feedback signal that varies by a frequency
lower than 1.6 Hz. If the feedback signal varies by a higher frequency
than 1.6 Hz, it will be dampened by the lowpass filter.
445
Value:
Off (DISABLE)
OK - same direction
OFF
(OK-same direction)
OK - both directions
(OK-both directions)
DC brake and start
(DC-BRAKE BEF. START)
Function:
This function makes it possible to 'catch' a rotating motor shaft, which is
no longer controlled by the adjustable frequency drive, e.g. because of a
mains drop-out. The function is activated each time a start command is
enabled. For the adjustable frequency drive to be able to 'catch' the ro-
tating motor shaft, the motor speed must be lower than the frequency
that corresponds to the frequency in parameter 202
high limit, f
Description of choice:
Disable
Select
0.00 sec.
OK - same direction
Select
the same direction when cutting in.
selected if in parameter 200
of Clockwise only
OK - both directions
Select
rections when cutting in.
DC brake and start
Select
able to brake the motor using the DC brake first, followed by start. It is
assumed that parameters 126-127/132
of higher 'Windmilling' (rotating motor) effects, the adjustable frequency
drive is not able to 'catch' a rotating motor without selecting
and start
Limitations:
5.0
-
-
-
451
Value:
0 - 500 %
0.02
MG.04.B8.02 - VLT is a registered Danfoss trademark
Flying start
.
MAX
[0] if this function is not required.
[1] if the motor shaft is only able to rotate in
OK - same direction
Output frequency range
.
[2] if the motor is able to rotate in both di-
[3] if the adjustable frequency drive is to be
DC brake
.
Too low inertia will lead to load acceleration, which can be dan-
gerous or prevent correct catching of a rotating motor. Use the
DC brake instead.
If the load is driven, e.g. by 'Windmilling' (rotating motor) ef-
fects, the unit may cut out because of overvoltage.
Flying start does not work at lower values than 250 rpm.
Speed PID feedforward factor
3 Programming
3
[0]
[1]
[2]
[3]
Output frequency,
[1] should be
a selection has been
are enabled. In the case
DC brake
100 %
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