Danfoss VLT FC 102 Programming Manual page 183

Parameter Descriptions
20-20 Feedback Function
Option: Function:
[6] Multi Setpoint Sets up the PID controller to
Max calculate the difference between
feedback 1 and setpoint 1,
feedback 2 and setpoint 2, and
feedback 3 and setpoint 3. It uses
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 uses the feedback/
setpoint pair with the least
difference between the 2.
NOTICE
If only 2 feedback signals are
used, set the non-used feedback
to [0] No Function in
Note that each setpoint reference
is the sum of its respective
parameter value
(parameter 20-21 Setpoint 1,
parameter 20-22 Setpoint 2, and
parameter 20-23 Setpoint 3) and
any other references that are
enabled (see parameter group 3-1*
References).
NOTICE
Set any unused feedback to [0] No function in
•
Parameter 20-00 Feedback 1 Source.
•
Parameter 20-03 Feedback 2 Source.
•
Parameter 20-06 Feedback 3 Source.
M0010001
Programming Guide
•
Parameter 20-00 Feedback
1 Source.
•
Parameter 20-03 Feedback
2 Source.
•
Parameter 20-06 Feedback
3 Source.
Danfoss A/S © 10/2019 All rights reserved.
The PID controller uses the feedback resulting from the
function selected in parameter 20-20 Feedback Function 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.
•
Be transmitted over various serial communication
protocols.
The frequency converter can be configured to handle
multi-zone applications. 2 different multi-zone applications
are supported:
•
Multi-zone, single setpoint
•
Multi-zone, multi-setpoint
Examples 1 and 2 illustrate the difference between the 2
applications:
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 parameter 20-20 Feedback Function to [3]
Minimum, and entering the desired pressure in
parameter 20-21 Setpoint 1. If any feedback is below the
setpoint, the PID controller increases the fan speed. If all
feedbacks are above the setpoint, the PID controller
decreases the fan speed.
3 3
®
181