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 oc-
curred.
419
Speed PID differential time
Value:
0.00 (OFF) - 200.00 ms
20.00 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 pro-
portional 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
Value:
5.0 - 50.0
5.0
Function:
It is possible to set a limit for the gain provided by the differentiator. Since
the D-gain increases at higher frequencies, limiting the gain may be use-
ful. This enables obtaining a pure D-gain at low frequencies and a
constant D-gain at higher frequencies.
Description of choice:
Select the required gain limit.
421
Speed PID lowpass filter time
Value:
20 - 500 ms
100 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 advant-
age, e.g. if there is a great amount of noise on the signal. See drawing.
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.
423
U1 voltage
Value:
0.0 - 999.0 V
par. 103
Function:
Parameters 423-428 are used when in parameter 101
Torque charac-
teristic
a selection has been made of
Special motor characteristic
[8]. It
is possible to determine a U/f characteristic on the basis of four definable
voltages and three frequencies. The voltage at 0 Hz is set in parameter
133
Start voltage
.
Description of choice:
Set the output voltage (U1) that is to match the first output frequency
(F1), parameter 424
F1 frequency
.
424
F1 frequency
Value:
0.0 - par. 426
F2 frequency
Par. 104
Motor 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
.
425
U2 voltage
Value:
0.0 - 999.0 V
par. 103
Function:
See parameter 423
U1 voltage
.
Description of choice:
Set the output voltage (U2) that is to match the second output frequency
(F2), parameter 426
F2 frequency.
426
F2 frequency
Value:
Par. 424
F1 frequency
- par. 428
F3 frequency
Par. 104
Motor
frequency
Function:
See parameter 423
U1 voltage
.
VLT
®
Decentral FCD 300 Design Guide
4 Programming
MG.90.S1.02 - VLT
®
is a registered Danfoss trademark
95
4