Fantech VLT 2800 Series Instruction Manual page 71

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418 Speed PID integral time
(SPEED INT. TIME)
Value:
20.00 - 999.99 ms (1000 = OFF)
Function:
The integral time determines how long the PID
regulator takes to correct the error. The greater
the error, the quicker the integrator frequency
contribution will increase. The integral time is the
time the integrator needs to achieve the same
change as the proportional amplification.
Description of choice:
Quick regulation is obtained through a short integral
time. However, if this time is too short, it can make
the process unstable. If the integral time is long,
major deviations from the required reference may
occur, since the process regulator will take long
to regulate if an error has occurred.
419 Speed PID differential time
(SPEED DIFF. TIME)
Value:
0.00 (OFF) - 200.00 ms
Function:
The differentiator does not react to a constant error.
It only makes a contribution when the error changes.
The quicker the error changes, the stronger the gain
from the differentiator will be. The contribution is
proportional to the speed at which errors change.
Description of choice:
Quick control is obtained by a long differential time.
However, if this time is too long, it can make the
process unstable. When the differential time is
0 ms, the D-function is not active.
420 Speed PID D- gain limit
(SPEED D-GAIN LIM)
Value:
5.0 - 50.0
Function:
It is possible to set a limit for the gain provided by the
differentiator. Since the D-gain increases at higher
= factory setting. () = display text [] = value for use in communication via serial communication port
70
VLT® 2800 Series
frequencies, limiting the gain may be useful. This
enables obtaining a pure D-gain at low frequencies
and a constant D-gain at higher frequencies.
100 ms
Description of choice:
Select the required gain limit.
421 Speed PID lowpass filter time
(SPEED FILT. TIME)
Value:
20 - 500 ms
Function:
Noise in the feedback signal is dampened by a first
order lowpass filter to reduce the noise's impact on the
regulation. This might be an advantage, e.g. if there is
a great amount of noise on the signal. See drawing.
20.00 ms
Description of choice:
If a time constant (t) of 100 ms 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 PID regulator will then only regulate a feedback
signal that varies with a frequency of less 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.
5.0
MG.28.A8.22 - VLT is a registered Danfoss trademark
100 ms

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