VLT
®
6000 HVAC
113
MG.60.B1.02 - VLT is a registered Danfoss trade mark
★
= factory setting. ( ) = display text [ ] = value for use in communication via serial communication port
Programming
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PID for process control
The PID controller maintains a constant process
condition (pressure, temperature, flow, etc.) and
adjusts motor speed on the basis of a reference/
setpoint and the feedback signal.
A transmitter supplies the PID controller with a
feedback signal from the process to indicate its actual
state. The feedback signal varies with the process
load.
This means that deviations occur between the
reference/setpoint and the actual process state. Such
deviations are evened out by the PID regulator, in that
it regulates the output frequency up or down in
relation to the deviation between the reference/
setpoint and the feedback signal.
The integral PID regulator in VLT 6000 HVAC units
has been optimised for use in HVAC applications.
This means that a number of specialised functions
are available in VLT 6000 HVAC units.
Formerly, it was necessary to get a BMS (Building
Management System) to handle these special
functions by installing extra I/O modules and by
programming the system.
Using the VLT 6000 HVAC, there is no need for extra
modules to be installed. For example, only one
required reference/setpoint and the handling of
feedback need to be programmed.
There is in-built a option for connecting two feedback
signals to the system, making two-zone regulation
possible.
Correction for voltage losses in long signal cables can
be carried out when using a transmitter with a voltage
output. This is done in parameter group 300
Min./
Max. scaling
.
Feedback
The feedback signal must be connected to a terminal
on the VLT frequency converter. Use the list below to
decide which terminal to use and which parameters
to program.
Feedback type
Terminal
Parameters
Pulse
33
307
Voltage
53, 54
308, 309, 310 or
311, 312, 313
Current
60
314, 315, 316
Bus feedback 1
68+69
535
Bus feedback 2
68+69
536
Please note that the feedback value in parameter 535/
536 Bus feedback 1 and 2 can only be set via serial
communication (not via the control unit).
Furthermore, the minimum and maximum feedback
(parameters 413 and 414) must be set to a value in
the process unit that corresponds to the minimum
and maximum scaling value for signals connected to
the terminal. The process unit is selected in parameter
415
Process units
.
Reference
In parameter 205
Maximum reference, Ref
MAX
, a
maximum reference that scales the sum of all
references, i.e. the resulting reference, can be set.
The
minimum reference
in parameter 204 indicates
the smallest value that the resulting reference can
assume.
The reference range cannot exceed the feedback
range.
If
Preset references
are required, set these in
parameters 211 to 214
Preset reference
. See
Reference type
on page 92.
See also
Reference handling
on page 89.
If a current signal is used as a feedback signal,
voltage can be used as analogue reference. Use the
list below to decide which terminal to use and which
parameters to program.
Reference type
Terminal
Parameters
Pulse
17 or 29
301 or 305
Voltage
53 or 54
308, 309, 310 or
311, 312, 313
Current
60
314, 315, 316
Preset reference
211, 212, 213, 214
Setpoints
418, 419
Bus reference
68+69
Please note that the bus reference can only be set via
serial communication.
NB!
Terminals that are not in use may preferably be
set to
No function
[0].
