Feedback Handling - Danfoss VLT AQUA Drive FC 202 Design Manual

Introduction

2.9.5 Feedback Handling

2 2
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
Illustration 2.13 Block Diagram of Feedback Signal Processing
Feedback handling can be configured to work with applications requiring advanced control, such as multiple setpoints and
multiple types of feedback. Three types of control are common.
Single zone, single setpoint
Single Zone Single Setpoint is a basic configuration. Setpoint 1 is added to any other reference (if any, see Reference
Handling) and the feedback signal is selected using 20-20 Feedback Function.
Multi-zone, single setpoint
Multi-Zone Single Setpoint uses two or three feedback sensors but only one setpoint. The feedback can be added,
subtracted (only feedback 1 and 2) or averaged. In addition, the maximum or minimum value can be used. Setpoint 1 is
used exclusively in this configuration.
If [13] Multi-Setpoint Min is selected, the setpoint/feedback pair with the largest difference controls the speed of the
frequency converter. [14] Multi-Setpoint Maximum attempts to keep all zones at or below their respective setpoints, while
[13] Multi-Setpoint Minattempts to keep all zones at or above their respective setpoints.
Example:
A two zone, two 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 [14] Multi-Setpoint Max is selected, Zone 1 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 [13] Multi-Setpoint
Min is selected, Zone 2 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).
24
Design Guide
Feedback 1
Feedback conv.
P 20-01
Feedback conv. Feedback 2
P 20-04
Feedback conv. Feedback 3
P 20-07
Danfoss A/S © Rev. 06/2014 All rights reserved.
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
MG20Z202