Specifications
Setpoint 1
P 20-21
Setpoint 2
P 20-22
Setpoint 3
P 20-23
Feedback 1 Source
P 20-00
Feedback 2 Source
P 20-03
Feedback 3 Source
P 20-06
Feedback conv.
P 20-01
Feedback conv.
P 20-04
Feedback conv.
P 20-07
Feedback 1
Feedback 2
Feedback 3
Feedback
Feedback Function
P 20-20
Multi setpoint min.
Multi setpoint max.
Feedback 1 only
Feedback 2 only
Feedback 3 only
Sum (1+2+3)
Dierence (1-2)
Average (1+2+3)
Minimum (1|2|3)
Maximum (1|2|3)
Setpoint to
Reference
Handling
0%
0%
0%
0%
130BA354.12
Illustration 2.22 Feedback Signal Processing
2.8.7 Feedback Conversion
In some applications it may be useful to convert the
feedback signal. One example of this is using a pressure
signal to provide flow feedback. Since the square root of
pressure is proportional to flow, the square root of the
pressure signal yields a value proportional to the flow. This
is shown in Illustration 2.23.
+
-
PID
P
P
P
130BA358.11
Ref.
signal
Desired
ow
P 20-07
FB conversion
Ref.
FB
Flow
FB
signal
Flow
P 20-04
P 20-01
Illustration 2.23 Feedback Conversion
2.8.8 Reference Handling
Details for Open Loop and Closed Loop operation.
The remote reference is comprised of:
•
Preset references.
•
External references (analog inputs, pulse
frequency inputs, digital potentiometer inputs
and serial communication bus references).
•
The preset relative reference.
•
Feedback controlled setpoint.
Up to 8 preset references can be programmed in the
frequency converter. The active preset reference can be
selected using digital inputs or the serial communications
bus. The reference can also be supplied externally, most
commonly from an analogue input. This external source is
selected by one of the 3 reference source parameters
(F-01 Frequency Setting 1, C-30 Frequency Command 2 and
C-34 Frequency Command 3).
Digipot is a digital potentiometer. This is also commonly
called a speed-up/speed-down control or a floating point
control. To set it up, program 1 digital input to increase
the reference while another digital input is programmed to
decrease the reference. A 3rd digital input can be used to
reset the digipot reference. All reference resources and the
bus reference are added to produce the total external
reference. The external reference, the preset reference or
the sum of the 2 can be selected to be the active
reference. Finally, this reference can by be scaled using
F-64 Preset Relative Reference.
Introduction VLT® HVAC Drive FC 102 Design Guide
34 MG16C102 - Rev. 2013-08-20
2
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