Danfoss VLT 2800 Design Manual page 99

Programming
421 Speed PID lowpass filter 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.
Feedback
Disturbed feedback signal
Lowpass lter
f = 10 Hz
g
Feedback
Filtered feedback signal
Illustration 4.17 Lowpass Filter Example
Description of choice:
If a time constant (t) of 100 ms is programmed, the cut-off
frequency for the lowpass filter is 1/0.1=10 RAD/s,
corresponding to (10/2 x π)=1.6 Hz. The PID regulator then
only regulates a feedback signal that varies with a
MG27E402
Design Guide
frequency of less than 1.6 Hz. If the feedback signal varies
by a higher frequency than 1.6 Hz, it is dampened by the
lowpass filter.
100 ms
423
Value:
0.0 - 999.0 V
Function:
Parameters 423-428 are used when [8] Special motor
characteristic has been selected in parameter 101 Torque
characteristic. It is possible to determine a U/f characteristic
on the basis of 4 definable voltages and 3 frequencies. The
voltage at 0 Hz is set in parameter 133 Start voltage.
0.6 t (Sec.)
Illustration 4.18 Output Voltage vs. Output Frequency
Description of choice:
Set the output voltage (U1) that is to match the first
output frequency (F1), parameter 424 F1 frequency.
424
Value:
0.0 - parameter 426 F2
frequency
Function:
See parameter 423 U1 voltage.
Description of choice:
Set the output frequency (F1) that is to match the first
output voltage (U1), parameter 423 U1 voltage.
0.6 t (Sec.)
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U1 voltage
F1 frequency
Parameter 104 Motor
par. 103
4 4
frequency
97