Danfoss VLT Brook Crompton Motor FCM 300 Design Manual page 59

Programming
parameters that are specific to the Process Regulator are
parameter 437 to parameter 444.
3.5.4 PID Functions
Unit of reference/feedback
When Process regulation, closed loop is selected in
parameter 100 Configuration the unit is defined in
parameter 416 Reference/feedback unit:
Feedback
A feedback range must be preset for the regulator. 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 frequency converter. 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
Pulse 3
Voltage 2
Current 1
Table 3.16
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 parameters 338/339 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
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.
®
VLT DriveMotor FCM Series
If preset references are desired, they are preset in
parameters 215 to 216 Preset reference. See description
Reference Function and Handling of References in parameter
214.
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
Pulse
Voltage
Current
Preset
references
Bus reference
Table 3.17
NOTICE
The bus reference can only be preset
via serial communication.
NOTICE
It is best to preset terminals that are not
being used to [0] No function.
Parameters
333, 327
Differentiator gain limit
332, 338, 339
If very rapid variations occur in an application in either the
331, 336, 337
reference signal or the feedback signal, the deviation
between the reference/setpoint and the process's actual
mode will change quickly. The differentiator 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 parameter 443 Process PID Differentiator
gain limit.
it is possible
MAX
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 parameter
444 Process PID lowpass filter time.
®
MG03BA02 - VLT is a registered Danfoss trademark
Terminal Parameters
3 333, 327
2 332, 338, 339
1 331, 336, 337
215-216
(241-247)
68+69
3 3
57