VLT
®
2800 Series
Programming
Lowpass filter
If there is a lot of noise in the feedback signal, these
can be dampened using an integrated lowpass filter.
A suitable lowpass filter time constant is preset.
If the lowpass filter is preset to 0.1 s, the cut-off
frequency will be 10 RAD/sec, corresponding to (10 / 2
x
π
) = 1.6 Hz. This will mean that all currents/voltages
that vary by more than 1.6 oscillations per second
will be dampened. In other words, there will only
be regulation on the basis of a feedback signal
that varies by a frequency of less than 1.6 Hz.
The appropriate time constant is selected in Speed
Regulation in parameter 421
Speed PID lowpass
filter time
and in Process Regulation in parameter
444
Process PID lowpass filter time
.
Inverse regulation
Normal regulation means that the motor speed is
increased when the reference/setpoint is greater
than the feedback signal. If it is necessary to run
inverse regulation, in which the speed is reduced
when the reference/setpoint is greater than the
feedback signal, parameter 437
PID normal/inverted
control
must be programmed at
Inverted
.
Anti Windup
In the factory the process regulator is preset with
an active anti windup function. This function means
that when either a frequency limit, a current limit or
a voltage limit is reached, the integrator is initialised
at a frequency corresponding to the present output
frequency. This is a means of avoiding the integration
of a variance between the reference and the process
’
s
actual mode that cannot be deregulated by means of
a change of speed. This function can be deselected
in parameter 438
Process PID anti windup
.
Starting conditions
In some applications the optimal setting of the
process regulator will mean that a relatively long
period of time will pass before the required process
condition is achieved. In these applications it can
be a good idea to define an output frequency to
which the frequency converter must run the motor
before the process regulator is activated. This is
done by programming a start frequency in parameter
439
Process PID start frequency
.
■
Handling of feedback
Feedback handling is depicted in this flowchart.
The flowchart shows which parameters can affect the
handling of feedback and how. A choice can be made
between voltage, current and pulse feedback signals.
✭
= factory setting. () = display text [] = value for use in communication via serial communication port
MG.28.E9.02 - VLT is a registered Danfoss trademark
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