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2 Parameter Description
2.17.3 20-2* Feedback & Setpoint
This parameter group is used to determine how the frequency converter's PID Controller will use the three possible feedback signals to control the output
frequency of the frequency converter. This group is also used to store the three internal setpoint references.
20-20 Feedback Function
2
Option:
[0]
Sum
[1]
Difference
[2]
Average
[3] *
Minimum
[4]
Maximum
[5]
Multi setpoint min
[6]
Multi setpoint max
190
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Function:
This parameter determines how the three possible feedbacks will be used to control the output
frequency of the frequency converter.
NB!
Any unused feedback must be set to "No function" in its Feedback Source pa-
rameter: 20-00, 20-03 or 20-06.
The feedback resulting from the function selected in par. 20-20 will be used by the PID Controller
to control the output frequency of the frequency converter. This feedback can also be shown on the
frequency converter's display, be used to control a frequency converter's analog output, and be
transmitted over various serial communication protocols.
The frequency converter can be configured to handle multi zone applications. Two different multi
zone applications are supported:
•
Multi zone, single setpoint
•
Multi zone, multi setpoint
The difference between the two is illustrated by the following examples:
Example 1 – Multi zone, single setpoint
In an office building, a VAV (variable air volume) water system must ensure a minimum pressure
at selected VAV boxes. Due to the varying pressure losses in each duct, the pressure at each VAV
box cannot be assumed to be the same. The minimum pressure required is the same for all VAV
boxes. This control method can be set up by setting
Minimum, and entering the desired pressure in par. 20-21. The PID Controller will increase the speed
of the fan if any one feedback is below the setpoint and decrease the speed of the fan if all feedbacks
are above the setpoint.
Example 2 – Multi zone, multi setpoint
MG.20.W1.22 - VLT is a registered Danfoss trademark
VLT Automation VT Drive FC322
Programming Guide
Feedback Function
, par. 20-20 to option [3],
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