Preset ref. msb Preset ref. lsb
Preset ref. 1
(par. 215)
00
Preset ref. 2
(par. 216)
01
Preset ref. 3
(par. 217)
10
Preset ref. 4
(par. 218)
11
If an external reference is required, this can either by
an analog reference or a pulse reference. If current is
used as a feedback signal, voltage can be used as an
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
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 add-
ed to the sum of the external references, which pro-
duces the active reference (X + XY). See drawing on
pages 62 and 63.
If relative references are to be used, parameter 214 is
to be set to Relative [1]. This makes the preset refer-
ences relative. Furthermore, Relative reference [4] can
be programmed on terminal 54 and/or 60. If an exter-
nal 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.
NOTE
Terminals that are not in use should pref-
erably be set to No function [0].
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
the error. The quicker the error changes, the stronger
the differentiator gain is. The differentiator gain can
thus be limited to allow setting of the reasonable dif-
ferentiation time for slow changes and a suitably quick
gain for quick changes. This is done in parameter 420,
Speed PID Differentiator gain limit.
Lowpass filter
If are oscillations of the current/voltage on the feed-
back signal, these can be dampened by means of a
lowpass filter. Set a suitable lowpass filter time con-
stant. This time constant represents the limit frequency
of the ripples occurring on the feedback signal. If the
lowpass filter has been set to 0.1s, the break frequency
will be 10 RAD/sec., corresponding to (10/2 x ʌ) = 1.6
Hz. This will mean that all currents/voltages that vary
by more than 1.6 oscillations per second will be re-
moved by the filter.
In other words, control will only be carried out on a
feedback signal that varies by a frequency of less than
1.6 Hz. Choose a suitable time constant in parameter
421, Speed PID Lowpass filter.
Quick discharge
This function is only available in EB units (extended
with brake) of the following type:
• VLT 5001-5052, 200-240 V
• VLT 5001-5102, 380-500 V
• 5001-5062, 525-600 V
This function is used for discharging the capacitors in
the intermediate circuit after the mains supply has
been interrupted. This is a useful function for servicing
the adjustable frequency drive and/or the motor instal-
lation. The motor must be stopped before quick dis-
charge is activated. If the motor acts as a generator,
quick discharge is not possible.
The quick discharge function can be selected via pa-
rameter 408. The function starts when the intermedi-
ate circuit voltage has dropped to a given value and
the rectifier has stopped.
In order to obtain the possibility of a quick discharge,
the adjustable frequency drive requires an external 24
V DC supply to terminals 35 and 36, as well as a suit-
able brake resistor on terminals 81 and 82.
For sizing of the discharge resistor for quick discharge,
see Brake Instructions MI.50.DX.XX.
NOTE
Quick discharge is only possible if the ad-
justable frequency drive has 24 Volts ex-
ternal DC supply and if an external brake/
discharge resistor has been connected.
VLT
®
5000 Series
202 MG.51.C5.22 - VLT
p
is a registered Danfoss trademark.
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