Decentral Solutions
When
Process regulation, closed loop
is selected
in parameter 100
Configuration
the unit is defined
in parameter 416
Process units.
Feedback
A feedback range must be preset for both regulators.
At the same time this feedback range limits the 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 variable frequency drive. If feedback
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
Parameters
Pulse
29, 33
305, 307, 327,
328
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 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
MAX
it is
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
analog reference Use the overview below to
determine which terminal is to be used and which
parameters are to be programmed.
Reference type
Terminal
Parameters
Pulse
29, 33
305, 307, 327,
328
Voltage
53
308, 309, 310
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.
NOTE
It is best to preset terminals that are not
being used to
No function
[0].
Differentiator gain limit
If very rapid variations occur in an application in 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 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
✭
= factory setting. () = display text [] = value for use in communication via serial communication port
MG.90.F2.22 - VLT is a registered Danfoss trademark
140
