20-20 Feedback Function
Option:
Function:
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
or
. Note that each setpoint reference
will be the sum of its respective parameter
value (
,
and
) 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.
NOTE
If only two feedback signals are used, the
feedback that is not to be used must be set
to
No Function
in
or
. Note that each setpoint reference
will be the sum of its respective parameter
value (
,
and
) and any other references
that are enabled (see par. group 3-1*).
NOTE
Any unused feedback must be set to “No function” in its
Feedback Source parameter:
,
or
.
The feedback resulting from the function selected in
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
to option [3], Minimum, and
entering the desired pressure in
. 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
126
MG.11.CB.02 - VLT
®
is a registered Danfoss trademark
3
3
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