Operating instructions

20-20 Feedback Function
Option: Function:
[5] Multi
Setpoint
Min
Multi-setpoint minimum [5] sets up the PID
Controller to calculate the difference between
Feedback 1 and Setpoint 1, Feedback 2 and
Setpoint 2, and Feedback 3 and Setpoint 3. It will
use the feedback/setpoint pair in which the
feedback is the farthest below its corresponding
setpoint reference. If all feedback signals are
above their corresponding setpoints, the PID
Controller will use the feedback/setpoint pair in
which the difference between the feedback and
setpoint is the least.
NOTE
If only two feedback signals are used,
the feedback that is not to be used must
be set to No Function in
par. 20-00 Feedback 1 Source,
par. 20-03 Feedback 2 Source or
par. 20-06 Feedback 3 Source. Note that
each setpoint reference will be the sum
of its respective parameter value
(par. 20-21 Setpoint 1, par. 20-22 Setpoint
2 and par. 20-23 Setpoint 3) and any
other references that are enabled (see
par. group 3-1*).
[6] Multi
Setpoint
Max
Multi-setpoint maximum [6] sets up the PID
Controller to calculate the difference between
Feedback 1 and Setpoint 1, Feedback 2 and
Setpoint 2, and Feedback 3 and Setpoint 3. It will
use the feedback/setpoint pair in which the
feedback is farthest above its corresponding
setpoint reference. If all feedback signals are
below their corresponding setpoints, the PID
Controller will use the feedback/setpoint pair in
which the difference between the feedback and
the setpoint reference is the least.
20-20 Feedback Function
Option: Function:
NOTE
If only two feedback signals are used,
the feedback that is not to be used must
be set to No Function in
par. 20-00 Feedback 1 Source,
par. 20-03 Feedback 2 Source or
par. 20-06 Feedback 3 Source. Note that
each setpoint reference will be the sum
of its respective parameter value
(par. 20-21 Setpoint 1, par. 20-22 Setpoint
2 and par. 20-23 Setpoint 3) and any
other references that are enabled (see
parameter group 3-1*).
NOTE
Any unused feedback must be set to “No function” in its
Feedback Source parameter: Par. 20-00 Feedback 1
Source, par. 20-03 Feedback 2 Source or
par. 20-06 Feedback 3 Source.
The feedback resulting from the function selected in
par. 20-20 Feedback Function 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) VLT HVAC
Drive 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
par. 20-20 Feedback Function to option [3], Minimum, and
entering the desired pressure in par. 20-21 Setpoint 1. 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.
Parameter Description
VLT
®
HVAC Drive Programming Guide
MG.11.CA.02 - VLT
®
is a registered Danfoss trademark 125
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