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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
Feedback Function
, par. 20-20 to option [3],
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
The previous example can be used to illustrate the use of multi zone, multi setpoint control. If the
zones require different pressures for each VAV box, each setpoint may be specified in par. 20-21,
20-22 and 20-23. By selecting
Multi setpoint minimum
, [5], in par. 20-20, Feedback Function, the
PID Controller will increase the speed of the fan if any one of the feedbacks is below its setpoint
and decrease the speed of the fan if all feedbacks are above their individual setpoints.
Sum
[0] sets up the PID Controller to use the sum of Feedback 1, Feedback 2 and Feedback 3 as
the feedback.
NB!
Any unused feedbacks must be set to
No Function
in par. 20-00, 20-03, or 20-06.
The sum of Setpoint 1 and any other references that are enabled (see par. group 3-1*) will be used
as the PID Controller’s setpoint reference.
Difference
[1] sets up the PID Controller to use the difference between Feedback 1 and Feedback
2 as the feedback. Feedback 3 will not be used with this selection. Only setpoint 1 will be used. The
sum of Setpoint 1 and any other references that are enabled (see par. group 3-1*) will be used as
the PID Controller’s setpoint reference.
Average
[2] sets up the PID Controller to use the average of Feedback 1, Feedback 2 and Feedback
3 as the feedback.
NB!
Any unused feedbacks must be set to
No Function
in par. 20-00, 20-03, or 20-06.
The sum of Setpoint 1 and any other references that are enabled (see par. group
3-1*) will be used as the PID Controller’s setpoint reference.
2 Parameter Description
VLT
®
AQUA Drive Programming Guide
164
MG.20.O4.02 - VLT
®
is a registered Danfoss trademark
2