VLT
®
Series 3500
71
★
= ROM default setting.
✔
= Normal Danfoss setup. Text in ( ) = display text. Figures in [ ] are used when communicating with the bus.
225 Adjustable Switching Frequency Modulation
(ASFM) (VAR.CARR.FR)
Value:
★
OFF (DISABLE)
[0]
✔
HIGH CARR @ LOW (ENABLE)
[1]
Low Carrier Frequency at Low Speed (const.carr.low)
[2]
Function:
To minimize acoustical motor noise, a high carrier fre-
quency can be chosen parameter 224. However, the output
of the drive must be derated when the carrier frequency is
above 4.5 kHz. This presents no problem at low speeds,
since the variable torque load will also be low. Reducing the
carrier frequency as the speed (and load) increases allows
the drive to produce full output. At extremely low speeds, a
high carrier frequency may produce too much motor volt-
age. Reducing carrier frequency at output speeds below 12
Hz can correct this problem.
Description of choice:
OFF maintains the carrier frequency set in parameter 224
at all output speeds.
HIGH CARR @ LOW (shown as ENABLE on some drives)
sets the drive to use the carrier frequency set in parameter
224 from minimum speed up to 50% speed. From 50%
speed to maximum speed, the drive’s carrier frequency de-
creases linearly to 4.5 kHz. This provides minimum motor
noise at low speed while eliminating the need to derate the
drive at maximum speed.
Low Carrier Frequency at Low Speed provides smooth op-
eration at extremely low output speeds by reducing the
PWM carrier frequency. At output frequencies below 12 Hz,
the PWM carrier frequency will automatically change to
match the drive’s operating speed and load, This choice is
only available on 460 V AC VLT Types 3575 through 3800
and on 208/230 V AC VLT Types 3542 through 3562. Be-
cause extremely low output speeds are not used, this is
generally not useful for variable torque applications.
232 Idle Running Current (NO LOAD CU)
Value:
0.0 to I
LIM
★
Depends on unit
Function:
This parameter allows setting a minimum motor current
value (idle running current). This allows one of the signal
relays to be activated when the motor does not use any
more current than the idle running current.
This function can be used for monitoring whether the V- belt
has broken.
I
LIM
is the current limit programmed in parameter 209.
Description of choice:
Relay 01 or 04 is activated though the setting of parameter
409 or 410 when the motor current drops below the value
set in this parameter and the drive is running at the maxi-
mum frequency set in parameter 202.
NOTE: For this feature to function, the drive must
be able to run up to the maximum frequency set in
parameter 202. If that may not be the case, use pa-
rameter 212, Warning Current Low, to perform this
function.
