1-80 Function at Stop
Option:
Function:
[1]
DC hold
Energizes motor with a DC holding current
(see
[2]
Motor check
Checks if a motor has been connected.
[3]
Pre-
magnetizing
Builds up a magnetic field while the motor is
stopped. This allows the motor to produce
torque quickly at subsequent start commands
(asynchronous motors only). This Pre-
magnetizing function does not help the very
first start command. Two different solutions
are available to pre-magnetize the machine
for the first start command:
1. Start the drive with a 0 RPM
reference and wait 2 to 4 rotor time
constants (see below) before
increasing the speed reference.
2a. Set par 1-71 Start Delay to the
desired pre-mag time (2 to 4 rotor
time constants - see below).
2b. Set par 1-72 to either [0] DC-hold
or [1] DC-Brake.
Set the DC-hold or DC-brake current
magnitude (2-00 or 2-01) to be
equal to I_pre-mag = Unom / (1.73 x
Xh)
Sample rotor time constants =
(Xh+X2) / (6.3*Freq_nom*Rr)
1kW = 0.2 seconds
10kW = 0.5 seconds
100kW = 1.7 seconds
1000kW = 2.5 seconds
[4]
DC Voltage
U0
When the motor is stopped, the P1-55 [0]
parameter defines the voltage at 0Hz.
[5]
Coast at low
reference
When the reference is below
1-81 Min Speed
for Function at Stop [RPM]
, the motor is discon-
nected from the frequency converter.
1-81 Min Speed for Function at Stop [RPM]
Range:
Function:
Size related
*
[0 - 600 RPM] Set the speed at which to activate
1-80 Function at Stop
.
1-82 Min Speed for Function at Stop [Hz]
Range:
Function:
Size related
*
[0.0 - 20.0 Hz] Set the output frequency at which
to activate
1-80 Function at Stop
.
The Precise Stop Functions are advantageous in applications
where high precision is required.
If you use a standard stop command the accuracy is
determined by the internal task time. That is not the case
when you use the precise stop function; it eliminates the task
time dependence and increases the accuracy substantially.
The frequency converter tolerance is normally given by its
task time. However, by using its special precise stop function
the tolerance is independent of the task time because the
stop signal immediately interrupts the execution of the
frequency converter program. The precise stop function
gives a highly reproducible delay from the stop signal is
given until the ramping down starts. A test must be done to
find this delay as it is a sum of sensor, PLC, FC and
mechanical parts.
To ensure optimum accuracy there should be at least 10
cycles during ramping down, see
and
.
The Precise Stop Function is set up here and enabled from DI
T29 or T33.
1-83 Precise Stop Function
Option:
Function:
[0]
*
Precise
ramp stop
Only optimal when the operational speed - of e.g.
the conveyor belt - is constant. This is an open
loop control. Achieves high repetitive precision at
the stopping point.
[1]
Cnt stop
with reset
Counts the number of pulses, typically from an
encoder and generates a stop signal after a pre-
programmed number of pulses -
- has been received at T29 or T33
[30].
This is a direct feedback with one-way closed loop
control.
The counter function is activated (starts timing) at
the edge of the start signal (when it changes from
stop to start). After each precise stop the number
of pulses counted during ramp down to 0 rpm is
reset.
[2]
Cnt stop
w/o reset
Same as [1] but the number of pulses counted
during ramp down to 0 rpm is deducted from the
counter value entered in
.
You can for example use this reset function to
compensate for the extra distance done during
ramping down and to reduce the impacts of
gradual wear of mechanical parts.
[3]
Speed
comp
stop
Stops at precisely the same point, regardless of
the present speed, the stop signal is delayed
internally when the present speed is lower than
the maximum speed (set in
The delay is calculated on the basis of the
reference speed of the frequency converter and
not on the basis of the actual speed. Please
therefore make sure that the frequency converter
Parameter Descriptions
FC 300 Programming Guide
MG.33.MB.02 - VLT
®
is a registered Danfoss trademark
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