VLT
®
2800 Series
that are specific to the Process Regulator are
parameter 437 to para me ter 444.
■ PID functions
U
nit of reference/feedback
When Speed regulation, closed loop is selected
in parameter 100 Configuration the unit of
reference/feedback is always rpm.
When Process regulation, closed loop is selected
in parameter 100 Configurat ion the unit is defined
in parameter 416 Process units.
F
eedback
A feedback range must be preset for both regulators.
Atthesametimethisfeedbackrangelimitsthe
potential reference range so that if the sum of all
references lies outside the feedback range, the
reference will be limited to lie within the feedback range.
The feedback signal must be connected to a
terminal on the frequency converter. If feedback
is selected on tw o 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 Parameters
Pulse 33 307, 327
Voltage 53 308, 309, 310
Current 60 314, 315, 316
A correction can be made for loss of voltage
in long signal cables when a transmitter with a
voltage
output is use d. 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
corr
esponding to the minimum and maximum scaling
values for signals that are connected to the terminal.
R
eference
In parameter 205 Maximum reference, Ref
MAX
it is
po
ssible to preset a maximum reference that scales
the sum of all references, i.e. the resulting reference.
The minimum reference in parameter 204 is
a
n 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 opt imal 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 Funct ion 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 w hich terminal is to be used and which
parametersaretobeprogrammed.
Reference type Terminal Parameters
Pulse 33 307, 327
Voltage 53 308, 309, 3 1 0
Current 60 314, 315, 316
Preset
references
215-218
Bus reference 68+69
Note that the bus reference can only be preset
via serial communication.
NB!:
It is best to
preset terminals that are not
being used to No function [0].
D
ifferentiator gain limit
If very rapid va riations occur in an application in
either the
reference signal or the feedback signal,
the deviation between the reference /setpoint and
the process’s actual m ode will change quickly. The
differe
ntiator can then become too dominant. This
is because it is react ing to the deviation between
the reference and the process’s actual mode,
and t
he quicker the variance changes the more
powerful the d ifferentiator’s frequency contribution
becomes. The differentiator’s frequency contribution
c
an therefore be limited in such a way that both
a reasonable differentiation time for slow changes
and an appropriate frequency contribut ion for quick
changes can be preset. This is done using the speed
regulation in parameter 420 Speed PID Differentiator
gain limit and Process regulat i on in parameter 443
Process PID Differentiator gain limit.
✭
= factory setting. () = display text [] = value for use in communication via serial communication port
MG.28.E9.02 - VLT is a registered Danfoss trademark
100
To Next Page
Loading...
Need help?
General
