Danfoss FC 102 Design Manual page 39

Introduction to VLT® HVAC D...
while [13] Multi Setpoint Min 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 [14] Multi Setpoint Max is
selected, Zone 1's setpoint and feedback are sent to the
PID controller, since this has the smaller difference
(feedback is higher than setpoint, resulting in a negative
difference). If [13] Multi Setpoint Min 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).
2.8.8 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 2.28.
Ref.
signal
Ref. +
P 20-01
-
P 20-04
Desired
P 20-07
FB conversion
ow
FB
FB
signal
P
Illustration 2.28 Feedback Conversion
MG11BC02
Design Guide
PID
P
Flow
Flow
P
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