Danfoss VLT 2800 Series, Operating Instructions Manual

Page: 51 / 103

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
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' a rotating
motor shaft, which is no longer controlled by the fre-
quency 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 direction [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
VLT
®
2800 Series
= factory setting, () = display text, [] = value for use in communication via serial communication port
50 MG.27.A2.02 - VLT
®
is a registered Danfoss trademark