VLT
®
4000 VT
Programming
■
PID overview
The block diagram below shows reference and
setpoint in relation to the feedback signal.
As can be seen, the remote reference is totalled
with setpoint 1 or setpoint 2. See also
Reference
handling
. Which setpoint is to be totalled with the
remote reference depends on the selection made
in parameter 417
Feedback function
.
■
Feedback handling
The feedback handling can be seen from the
block diagram on the next page.
The block diagram shows how and by which
parameters the feedback handling can be affected.
Options as feedback signals are: voltage, current,
pulse and bus feedback signals. In zone regulation,
feedback signals must be selected as voltage inputs
(terminals 53 and 54). Please note that
Feedback 1
consists of bus feedback 1 (parameter 535) totalled
with the feedback signal value of terminal 53.
Feedback
2
consists of bus feedback 2 (parameter 536) totalled
with the feedback signal value of terminal 54.
In addition, the VLT 4000 VT has an integral calculator
capable of converting a pressure signal into a "linear
flow" feedback signal. This function is activated in
parameter 416
Feedback conversion
.
The parameters for feedback handling are active both
in closed and open loop modes. In
open loop
, the
present temperature can be displayed by connecting
a temperature transmitter to a feedback input.
In a closed loop, there are - roughly speaking -
three possibilities of using the integral PID regulator
and set-point/ feedback handling:
1. 1 setpoint and 1 feedback
2. 1 setpoint and 2 feedbacks
3. 2 Setpoints and 2 feedbacks
1 setpoint and 1 feedback
If only 1 setpoint and 1 feedback signal are used,
parameter 418
Setpoint 1
will be added to the remote
reference. The sum of the remote reference and
Setpoint 1
becomes the resulting reference, which will
then be compared with the feedback signal.
1 setpoint and 2 feedbacks
Just like in the above situation, the remote reference
is added to
Setpoint 1
in parameter 418. Depending
on the feedback function selected in parameter
417
Feedback function
, a calculation will be made
of the feedback signal with which the sum of the
references and the setpoint is to be compared. A
description of the individual feedback functions is
given in parameter 417
Feedback function
.
2 Setpoints and 2 feedbacks
Used in 2-zone regulation, where the function selected
in parameter 417
Feedback function
calculates the
setpoint to be added to the remote reference.
MG.40.A7.22 - VLT is a registered Danfoss trademark
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