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

Chapter 4 Explanation of Functions

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 examples 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

Data or range of data

Description

Restart mode after

b088

00

Start with 0 Hz (See example 1.)

01

Start with matching frequency (See example 2.)

FRS

 

02

Restart with input frequency (See example 3.)

 

 

Retry wait time before

b003

0.3 to 100. (s)

Time to wait until restarting the motor

motor restart

 

 

 

Restart frequency

b007

0.00 to 400.0 (Hz)

Setting of the minimum level for frequency

threshold

adjustment

 

 

Active frequency

b028

"0.20 x rated current" to

 

matching, scan start

 

"2.00 x rated current"

 

frequency

 

 

 

 

 

Active frequency

 

 

 

matching, scan-time

b029

0.10 to 30.00 (s)

 

constant

 

 

 

Active frequency

 

00

Frequency set when the inverter output has

 

been shut off

matching, restart

b030

 

01

Maximum frequency

frequency select

 

 

02

Newly set frequency

 

 

(Example 1) Restarting with 0 Hz

(Example 2) Restarting with matching frequency

FW

FRS

Motor speed

0

 

 

 

 

FW

 

 

 

 

 

 

 

 

FRS

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Free-running

 

 

 

Free-running

 

 

 

 

Motor

 

 

 

 

 

 

 

 

speed

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Restarting with 0 Hz

0

 

 

b003

 

 

 

 

Restarting with

 

 

 

 

 

 

 

 

 

 

 

 

 

 

matching frequency

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.

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.

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Image 110
Hitachi SJ700-2 instruction manual Free-run stop FRS function