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Chapter 4
4.2.47 Free-run stop (FRS) function
The free-run stop (FRS) function allows you to shut off the
inverter output to let the motor start free-running.
You can effectively use this function when stopping the motor
with a mechanical brake (e.g., electromagnetic brake). If an
attempt is made to forcibly stop the motor with a mechanical
brake while the inverter keeps its output, the inverter may trip
because of overcurrent.
To use this function, assign function "11" (FRS) to one of the terminal [1] to [8] functions (C001 to C008).
The free-run stop (FRS) function operates as long as the FRS terminal is on. When the FRS terminal is turned off, the
inverter restarts the motor after the retry wait time (b003). However, the inverter does not restart the motor if the
digital operator (02) has been specified for the run command source setting (A002). To restart the motor in such status,
enter a new operation command.
You can select the inverter output mode for restarting with the restart mode after FRS (b088) from starting the motor
with 0 Hz, starting the motor with a matching frequency, and restarting the motor with the input frequency. (See
Example 1, 2, and 3.)
Even when restarting with matching frequency has been selected, the inverter restarts the motor with 0 Hz if it detects
a frequency lower than the restart frequency threshold (b007).
The settings, including that of the FRS terminal, which you make for this function will affect the inverter operation at
recovery of the motor from the free-running status.
Item
Function code
Restart mode after
FRS
Retry wait time before
motor restart
Restart frequency
threshold
Active frequency
matching, scan start
frequency
Active frequency
matching, scan-time
constant
Active frequency
matching, restart
frequency select
(NOTE)<>:applied for 75 to 150kW
(Example 1) Restarting with 0 Hz
FW
FRS
Motor
speed
0
The inverter restarts the motor with 0 Hz regardless
of the motor speed. The setting of retry wait time is
ignored for restarting with 0 Hz.
If the inverter restarts the motor with 0 Hz when the
motor speed is high, the inverter may trip because of
overcurrent.
Data or range of data
00
b088
01
02
b003
0.3 to 100. (s)
b007
0.00 to 400.0 (Hz)
CT mode
0.00 to 2.00 x rated current
<0.00 to 1.80 x rated current>
b028
VT mode
0.00 to 1.50 x rated current
<0.00 to 1.50 x rated current>
b029
0.10 to 30.00 (s)
00
b030
01
02
Free-running
Restarting with 0 Hz
Explanation of Functions
Related code
b088: Restart mode after FRS
b003: Retry wait time before motor restart
b007: Restart frequency threshold
b028: Active frequency matching, scan start frequency
b029: Active frequency matching, scan-time constant
b030: Active frequency matching, restart frequency select
C001 to C008: Terminal [1] to [8] functions
Start with 0 Hz (See Example 1.)
Start with matching frequency (See Example 2.)
Restart with input frequency (See Example 3.)
Time to wait until restarting the motor
Setting of the minimum level for frequency
adjustment
Frequency set when the inverter output has been
shut off
Maximum frequency
Newly set frequency
(Example 2) Restarting with matching frequency
FW
FRS
Motor
speed
0
The inverter waits for the retry wait time after the FRS terminal
has been turned off, detects the motor speed (frequency), and
restarts the motor with the matching frequency without
stopping it. If the inverter trips because of overcurrent when it
restarts the motor with matching frequency, prolongs the retry
wait time.
Even when restarting with matching frequency has been
selected, the inverter may start the motor with 0 Hz if:
1) the output frequency is no more than half the base
frequency or
2) the voltage induced on the motor is attenuated quickly.
4-52
Description
Free-running
b003
Restarting with
matching frequency
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