Danfoss VLT Series Design Manual page 46

2. Introduction to the VLT HVAC Drive
difference). If
to the PID controller, since this has the larger difference (feedback is lower than setpoint, resulting
in a positive difference).
2
2.8.9. 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.
Another application that may benefit from feedback conversion is compressor control. In such
applications, the output of a pressure sensor may be converted to the refrigerant temperature
using the equation:
Temperature
where A1, A2 and A3 are refrigerant-specific constants.
46
Multi-setpoint Max [13] is selected, the setpoint and feedback of Zone 2 are sent
A
2
=
( ( + 1 ) − 1 )
ln pressure A
MG.11.B4.22 - VLT
A
− 3
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VLT ® HVAC Drive Design Guide