Pid For Process Control - Danfoss VLT 5000 Series Operating Instructions Manual

PID for process control

Feedback
The feedback signal must be connected to a terminal
on the frequency converter. Use the list below to
decide which terminal is to be used and which
parameters are to be programmed.
Feedback type Terminal
Pulse 33
Voltage 53
Current 60
Furthermore, the minimum and maximum feedback
(parameters 414 and 415) must be set to a value in
the process unit that corresponds to the minimum
and maximum value on the terminal.
Select process unit in parameter 416.
Reference
A minimum and a maximum reference can be set (204
and 205), which limit the sum of all references. The
reference range cannot exceed the feedback range.
If one or several setpoint references are required,
the simplest way is to set such reference directly
in parameters 215 to 218. Select between the
preset references by connecting terminals 16, 17,
29, 32 and/or 33 to terminal 12. Which terminals
that are used depends on the choice made in the
parameters of the various terminals (parameters
300, 301, 305, 306 and/or 307). Use the table
below when selecting preset references.
Preset ref. msb
Preset ref. 1 0
(par. 215)
Preset ref. 2 0
(par. 216)
Preset ref. 3 1
(par. 217)
Preset ref. 4 1
(par. 218)
If an external reference is required, this can either
be an analogue or a pulse reference. If current
is used as a feedback signal, only voltage can
be used as an analogue reference. Use the
following list to decide which terminal to use and
which parameters to program.
Reference type Terminal
Pulse 17 or 29
Voltage 53 or 54
Current 60
90
Relative references can be programmed. A relative
reference is a percentage value (Y) of the sum of
the external references (X). This percentage value
is added to the sum of the external references,
which produces the active reference (X + XY). See
section Handling of multi references.
If relative references are to be used, parameter 214 is to
Parameters
be set to Relative [1]. This makes the preset references
307
relative. Furthermore, Relative reference [4] can be
308, 309, 310
programmed on terminal 54 and/or 60. If an external
314, 315, 316
relative reference is selected, the signal on the input will
be a percentage value of the full range of the terminal.
The relative references are added with signs.
Inverse control
If the drive has to react with increasing speed on
and increasing feedback, Inverse must be selected in
parameter 437. Normal control means that the motor
speed decreases when the feedback signal increases.
Anti Windup
The process controller comes with the anti windup
function in active position. This function ensures
that when either a frequency limit or a torque limit
is reached, the integrator will be set to a gain that
corresponds to the actual frequency. This avoids
integrating on an error that cannot in any case be
compensated for by means of a speed change. This
Preset ref. lsb
function can be disabled in parameter 438.
0
Start-up conditions
1
In some applications, optimum setting of the process
controller will mean that it takes an excessive time
0
for the desired process value to be reached. In
such applications it might be an advantage to fix a
1
motor frequency to which the frequency converter is
to bring the motor before the process controller is
activated. This is done by programming a Process
PID start frequency in parameter 439.
Differentiator gain limit
If there are quick changes in reference or feedback
in a given application - which means that the error
changes swiftly - the differentiator may soon become
too dominant. This is because it reacts to changes in
Parameters
the error. The quicker the error changes, the stronger
301 or 305
the differentiator gain is. The differentiator gain can
308, 309, 310 or
thus be limited to allow setting of the reasonable
311, 312, 313
differentiation time for slow changes and a suitably
314, 315, 316
®
VLT 5000 Series
NB!:
Terminals that are not in use should preferably
be set to No function [0].
MG.51.A9.02 - VLT is a registered Danfoss trademark