Danfoss VLT AQUA Drive Design Manual page 31

VLT ® AQUA Drive Design Guide 2. Introduction to the VLT AQUA Drive
Multi-zone, Multi-setpoint
applies an individual setpoint reference to each feedback. The drive's closed-loop controller choo-
Multi-setpoint
ses one pair to control the drive based on the user's selection in par. 20-20. If
Max
[14] is selected, the setpoint/feedback pair with the smallest difference controls the speed
2
of the drive. (Note that a negative value is always smaller than a positive value).
Multi-setpoint Min
If [13] is selected, the setpoint/feedback pair with the largest difference controls
Multi-setpoint Maximum
the speed of the drive. [14] attempts to keep all zones at or below their
Multi-setpoint Min
respective setpoints, while [13] attempts 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
Multi-setpoint Max
2 setpoint is 4.4 bar and the feedback is 4.6 bar. If [14] is selected, Zone 1's
setpoint and feedback are sent to the PID controller, since this has the smaller difference (feed-
Multi-setpoint Min
back is higher than setpoint, resulting in a negative difference). If [13] is
selected, Zone 2's setpoint and feedback is sent to the PID controller, since this has the larger
difference (feedback is lower than setpoint, resulting in a positive difference).
2.9.10. 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
below.
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MG.20.N2.22 - VLT ® is a registered Danfoss trademark.