Pid For Process Control - Danfoss VLT 7000 Series Manual

PID for process control

The PID controller maintains a constant process
con-dition (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
feed-back 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 7000 Booster units
has been optimised for use in HVAC applications.
This means that a number of specialised functions
are available in VLT 7000 Booster 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 7000 Booster, 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 frequency converter. Use the
list below to decide which terminal to use and
which parameters to program.
Feedback type Terminal
Pulse 33
Voltage 53, 54
Current 60
Bus feedback 1 68+69
Bus feedback 2 68+69
= factory setting. () = display text [] = value for use in communication via serial communication port
MG.70.A1.02 - VLT is a registered Danfoss trademark
Parameters
307
308, 309, 310 or
311, 312, 313, 314
315, 316
535
536
VLT® 7000 Booster
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
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.
See also Reference handling.
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
Pulse 17 or 29
Voltage 53 or 54
Current 60
Preset reference
214
Setpoints
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].
,
MAX
Parameters
301 or 305
308, 309, 310 or
311, 312, 313
314, 315, 316
211, 212, 213,
418, 419
81