VLT
®
5000 Series
Description of choice:
Quick control is obtained by a high gain, but if the
gain is too high, the process may become unstable.
441
441 Process PID integral time
(PROC. INTEGR. T.)
Value:
0.01 - 9999.99 sec. (OFF)
✭ OFF
Function:
The integrator provides an increasing gain at a con-
stant error between the set point and the feedback
signal. The greater the error, the quicker the gain
will increase. The integral time is the time needed by
the integrator to reach the same gain as the propor-
tional gain.
The gain is proportional to the speed at which the
error changes.
Used together with
Process control, closed loop (pa-
rameter 100).
Description of choice:
Quick control is obtained at a short integral time.
However, this time may become too short, which can
make the process unstable.
If the integral time is long, major deviations from the
required set point may occur, since the process reg-
ulator will take a long time to regulate in relation to a
given error.
442
442 Process PID differentiation time
(PROC. DIFF. TIME)
Value:
0.00 (OFF) - 10.00 sec.
✭ 0.00 sec.
Function:
The differentiator does not react to a constant error.
It only provides a gain when the error changes. The
quicker the error changes, the stronger the gain from
the differentiator.
The gain is proportional to the speed at which the
error changes.
Used together with Process control, closed loop (pa-
rameter 100).
Description of choice:
Quick control is obtained with a long differentiation
time. However, this time may become too long,
which can make the process unstable.
443
443 Process PID diff. gain limit
(PROC. 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 error occur.
Used together with Process control, closed loop (pa-
rameter 100).
Description of choice:
Select a limit to differentiator gain as required.
444
444 Process PID lowpass filter time
(PROC 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 control. This can be an advantage e.g.
if there is a lot of noise on the signal.
Used together with Process control, closed loop (pa-
rameter 100).
Description of choice:
Select the desired time constant (
). If a time
constant (
) of 100 ms is programmed, the break fre-
quency for the lowpass filter will be 1/0.1 = 10 RAD/
sec., corresponding to (10/2 x
) = 1.6 Hz.
The process regulator will thus o
nly regulate a feed-
back signal that varies by a frequency lower than 1.6
Hz. If the feedback signal varies by a higher fre-
✭
= factory setting. () = display text [] = value for use in communication via serial communication port
MG.51.A1.02 - VLT is a registered Danfoss trade mark
153
Programming
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