Danfoss VLT FCD 303 Operating Instructions Manual page 69

is selected on two terminals simultaneously, the
two signals will be added together.
Use the overview below to determine which
terminal is to be used and which parameters
are to be programmed.
Feedback type Terminal
Pulse 29, 33
Voltage 53
Current 60
A correction can be made for loss of voltage
in long signal cables when a transmitter with a
voltage output is used. This is done in parameter
group 300 Min./Max scaling.
Parameters 414/415 Minimum/Maximum feedback
must also be preset to a value in the process unit
corresponding to the minimum and maximum scaling
values for signals that are connected to the terminal.
Reference
In parameter 205 Maximum reference, Ref
possible to preset a maximum reference that scales
the sum of all references, i.e. the resulting reference.
The minimum reference in parameter 204 is
an expression of the minimum value that the
resulting reference can assume.
All references will be added together and the sum
will be the reference against which regulation will
take place. It is possible to limit the reference range
to a range that is smaller than the feedback range.
This can be an advantage if you want to avoid
an unintentional change to an external reference
making the sum of the references move too far
away from the optimal reference. The reference
range cannot exceed the feedback range.
If preset references are desired, they are preset
in parameters 215 to 218 Preset reference.
See description Reference Function and
Handling of References.
If a current signal is used as the feedback signal,
it will only be possible to use voltage as an
analogue reference. Use the overview below to
determine which terminal is to be used and which
parameters are to be programmed.
Reference type Terminal
Pulse 29, 33
Voltage 53
Current 60
Preset
references
Bus reference 68+69
= factory setting. () = display text [] = value for use in communication via serial communication port
MG.04.B7.02 - VLT is a registered Danfoss trademark
Note that the bus reference can only be preset
via serial communication.
Parameters
305, 307, 327, 328
Differentiator gain limit
308, 309, 310
If very rapid variations occur in an application in
314, 315, 316
either the reference signal or the feedback signal,
the deviation between the reference/setpoint and
the process's actual mode will change quickly.
Thedifferentiator can then become too dominant. This
is because it is reacting to the deviation between
the reference and the process's actual mode,
and the quicker the variance changes the more
powerful the differentiator's frequency contribution
becomes. The differentiator's frequency contribution
can therefore be limited in such a way that both
a reasonable differentiation time for slow changes
and an appropriate frequency contribution for quick
changes can be preset. This is done using the speed
it is
MAX
regulation in parameter 420 Speed PID Differentiator
gain limit and Process regulation in parameter 443
Process PID Differentiator gain limit.
Lowpass filter
If there is a lot of noise in the feedback signal, these
can be dampened using an integratedlowpass 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
Parameters
when the reference/setpoint is greater than the
305, 307, 327, 328
feedback signal, parameter 437 PID normal/inverted
308, 309, 310
control must be programmed at Inverted .
314, 315, 316
215-218
Anti Windup
®
VLT FCD Series
NB!:
It is best to preset terminals that are not
being used to No function [0].
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