Technical data

VLT
®
2800 Series
Programming
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
(PROCFILTERTIME)
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’simpacton
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.,
corresponding 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. I
fthe
feedback signal varies by a higher frequency than 1.6
Hz, it will be dampened by the lowpass filter.
445 Flying start
(FLYINGSTART)
Value:
✭Off (DISABLE)
[0]
OK - same direction
(OK-SAME DIRECTION)
[1]
OK - both directions
(OK-BOTH DIRECTIONS)
[2]
DC brake and start
(DC-BRAKE BEF. START)
[3]
Function:
This function makes it possible to ’catch’ arotating
motor shaft, which is no longer controlled by the
frequency converter, e.g. because of a mains
drop-out. The function is activated each time a start
command is enabled. For the frequency converter
to be able to ’catch’ the rotating motor shaft, the
motor speed must be lower than the frequency
that corresponds to the frequency in parameter
202 Output frequency, high limit, f
MAX
.
Description of choice:
Select Disable [0] if this function is not required.
Select OK - same direct ion [1] if the motor shaft
is only able to rotate in the same direction when
cutting in. OK - same direction [1] should be
selected if in parameter 200 Output frequency range
a selection has been of Clockwise only .
Select OK - both direc t i ons [2] if the motor is able
to rotate in both directions when cutting in.
Select DC brake and start [3] if the frequency converter
is to be able to brake the motor using the DC brake
first, followed by start. It is assumed that parameters
126-127/132 DC brake are enabled. In the case
of higher ’Windmilling’ (rotating motor) effects, the
frequency converter is not able to ’catch’ arotating
motor without selecting DC brake and start .
Limitations:
- Too low inertia will lead to load acceleration, which
can be dangerous or prevent correct catching of a
rotating motor. Use the DC brake instead.
- If the load is driven, e.g. by ’Windmilling’
(rotating motor) effects, the unit may cut
out because of overvoltage.
✭
= factory setting. () = display text [] = value for use in communication via serial communication port
MG.28.A9.02 - VLT is a registered Danfoss trademark
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