Danfoss VLT AutomationDrive FC 302 Design Manual page 180

Basic Operating Principles ...
11.2.3 Feedback Handling
Feedback handling can be configured to work with applications requiring advanced control, such as multiple setpoints and
multiple types of feedback. See Illustration 11.4. Three types of control are common:
Single zone (single setpoint)
This control type is a basic feedback configuration. Setpoint 1 is added to any other reference (if any) and the feedback
signal is selected.
Multi-zone (single setpoint)
This control type uses 2 or 3 feedback sensors but only 1 setpoint. The feedback can be added, subtracted, or averaged. In
addition, the maximum or minimum value can be used. Setpoint 1 is used exclusively in this configuration.
Multi-zone (setpoint/feedback)
The setpoint/feedback pair with the largest difference controls the speed of the drive. The maximum value attempts to keep
all zones at or below their respective setpoints, while the minimum value attempts to keep all zones at or above their
respective setpoints.
Example
A 2-zone, 2-setpoint application. Zone 1 setpoint is 15 bar, and the feedback is 5.5 bar. Zone 2 setpoint is 4.4 bar, and the
feedback is 4.6 bar. If maximum is selected, the zone 2 setpoint and feedback are sent to the PID controller, since it has the
smaller difference (feedback is higher than setpoint, resulting in a negative difference). If minimum is selected, the zone 1
setpoint and feedback is sent to the PID controller, since it has the larger difference (feedback is lower than setpoint,
resulting in a positive difference).
Setpoint 1
P 20-21
Setpoint 2
P 20-22
11 11
Setpoint 3
P 20-23
Feedback 1 Source
P 20-00
Feedback 2 Source
P 20-03
Feedback 3 Source
P 20-06
Illustration 11.4 Block Diagram of Feedback Signal Processing
178
VLT® AutomationDrive FC 302
Feedback 1
Feedback conv.
P 20-01
Feedback conv. Feedback 2
P 20-04
Feedback conv. Feedback 3
P 20-07
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0%
0%
Multi setpoint min.
Multi setpoint max.
0%
Feedback 1 only
Feedback 2 only
Feedback 3 only
Sum (1+2+3)
0%
Di erence (1-2)
Average (1+2+3)
Minimum (1|2|3)
Maximum (1|2|3)
Feedback Function
P 20-20
Setpoint to
Reference
Handling
Feedback
MG38C202