VLT
®
8000 AQUA
Programming
■ 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 8000 AQUA units
have been optimised for use in water applications.
This means that a number of specialised functions
are available in VLT 8000 AQUA units.
Using the VLT 8000 AQUA, 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 a built in option for connecting two
feed-back signals to the system.
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.
F
eedback
The feedback signal must be connected to a
terminal on the 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
p
arameter 415 Process units.
R
eference
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
211to214Preset reference.SeeReference type.
See also Reference handling.
If a current signal is used as a feedback signal,
voltage can be used as analog 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].
I
nverse regulation
Normal regulation means that the motor speed
increases when the reference/setpoint is higher than
the feedback signal. If there is a need for inverse
regulation, in which the speed is reduced when
the reference/setpoint is higher than the feedback
signal, inverse must be programmed in parameter
420 PID normal/inverse control.
A
nti Windup
The process regulator is factory preset with an active
anti-windup function. This function ensures that
when either a frequency limit, current limit or voltage
limit is reached, the integrator will be initialised for
a frequency that corresponds to the present output
frequency. This avoids integration on a deviation
between the reference/setpoint and the actual state
of the process, the controller of which is not possible
by means of a speed change. This function can be
disabled in parameter 421 PID anti windup.
✭
= factory setting. () = display text [] = value for use in communication via serial communication port
MG.83.A2.02 - VLT is a registered Danfoss trademark
137
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