Danfoss VLT FCD 311 Design Manual page 88

NB!:
Parameters 417-421 are only used, if in pa-
rameter 100 Configuration the selection made
is Speed regulation, closed loop [1].
417 Speed PID proportional gain
417
(SPEED PROP GAIN)
Value:
0.000 (OFF) - 1.000
Function:
Proportional gain indicates how many times the fault
(deviation between the feedback signal and the set-
point) is to be amplified.
Description of choice:
Quick regulation is obtained at high amplification, but
if the amplification is too high, the process may be-
come unstable in the case of overshooting.
418 Speed PID integral time
418
(SPEED INT. TIME)
Value:
20.00 - 999.99 ms (1000 = OFF)
Function:
The integral time determines how long the PID regu-
lator 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 propor-
tional 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, ma-
jor 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
419
(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
= factory setting. () = display text [] = value for use in communication via serial communication port
88
®
VLT FCD Series
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 pro-
cess unstable. When the differential time is 0 ms,
the D-function is not active.
0.010
420 Speed PID D- gain limit
420
(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 frequencies, limiting the gain may be useful.
This enables obtaining a pure D-gain at low frequen-
cies and a constant D-gain at higher frequencies.
Description of choice:
Select the required gain limit.
100 ms
421 Speed PID lowpass filter time
421
(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
MG.04.A1.02 - VLT is a registered Danfoss trade mark
5.0
100 ms