VLT
®
4000 VT
Programming
time needed by the integrator to reach the same gain
as the proportional gain for a given deviation.
Used in
Closed loop
[1] (parameter 100).
Description of choice:
Fast regulation is obtained in connection with a
short integration time. However, this time may be
too short, which means that the process may be
destabilised as a result of overswings.
If the integral time is long, major deviations from
the required set point may occur, since the
process regulator will take a long time to regulate
in relation to a given error.
425 PID differentiation time
(PID DIFF. TIME)
Value:
0.00 (OFF) - 10.00 sec.
✭
OFF
Function:
The differentiator does not react to a constant error. It
only contributes when the error changes. The quicker
the error changes, the stronger the contribution from
the differentiator will be. This influence is proportional
to the speed by which the deviation changes.
Used in
Closed loop
[1] (parameter 100).
Description of choice:
Fast regulation can be obtained by means of a
long differentiation time. However, this time may
be too long, which means that the process may be
destabilised as a result of overswings.
426 PID differentiator gain limit
(PID 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 obtaining a pure differentiator gain at
slow changes and a constant differentiator gain where
quick changes to the deviation are made.
Used in
Closed loop
[1] (parameter 100).
Description of choice:
Select a limit to differentiator gain as required.
427 PID lowpass filter time
(PID FILTER TIME)
Value:
0.01 - 10.00
✭
0.01
Function:
Oscillations on the feedback signal are dampened by
the lowpass filter in order to reduce their impact on
the process regulation. This can be an advantage
if there is a lot of noise on the signal.
Used in
Closed loop
[1] (parameter 100).
Description of choice:
Select the desired time constant (
τ
). If a time constant
(
τ
) of 0.1 s is programmed, the break 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.
If the feedback signal varies by a higher frequency than
1.6 Hz, the Process regulator will not react.
MG.40.A7.22 - VLT is a registered Danfoss trademark
107
