VLT
®
5000 Series
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 analogue reference or a pulse reference. If cur-
rent is used as a feedback signal, voltage can be
used as an analogue reference. Use the list below
to decide which terminal to use and which parame-
ters to program.
R
eference type
Te
rminal
P
arameters
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
added to the sum of the external references, which
produces 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
references relative. Furthermore, Relative reference
[4] can be programmed on terminal 54 and/or 60. If
an external 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.
NB!:
Terminals that are not in use
should preferably be set to No function [0].
D
ifferentiator 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 rea-
sonable differentiation time for slow changes and a
suitably quick gain for quick changes. This is done in
parameter 420, Speed PID Differentiator gain limit .
L
owpass 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
constant. This time constant represents the limit fre-
quency 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
) = 1.6 Hz. This will mean that all cur-
rents/voltages that vary by more than 1.6 oscillations
per second will be removed 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 pa-
rameter 421, Speed PID Lowpass filter .
■ Quick discharge
This function calls for a VLT of type EB. This function
is used for discharging the capacitors in the interme-
diate circuit after the mains supply has been
interrupted. This is a useful function for servicing the
VLT frequency converter and/or the motor installa-
tion. The motor must be stopped before quick
discharge is activated. If the motor acts as a genera-
tor, quick discharge is not possible.
The quick discharge function can be selected via
parameter 408. The function starts when the inter-
mediate circuit voltage has declined to a given value
and the rectifier has stopped.
In order to obtain the possibility of a quick discharge,
the VLT frequency converter requires an external 24
V DC supply to terminals 35 and 36, as well as a
suitable brake resistor on terminals 81 and 82.
For sizing of the discharge resistor for quick dis-
charge, see Brake Instructions MI.50.DX.XX.
NB!:
Quick discharge is only possible if the VLT
frequency converter has 24 Volts external DC
supply and if an external brake/discharge resistor
has been connected.
Before servicing the installation (VLT
frequency converter + motor), it must be
checked that the intermediate circuit volt-
age is below 60 V DC. This is done by measuring
terminals 88 and 89, load-sharing.
MG.51.A1.02 - VLT is a registered Danfoss trade mark
99
Special functions
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