Failsafe System Which Uses The Inverter - Mitsubishi Electric 800 Series Instruction Manual

Failsafe system which uses the inverter

Checkpoint
Countermeasures are taken against
electrical corrosion on the motor
bearing.

Recommended common mode choke: FT-3KM F series FINEMET® common mode choke cores manufactured by Hitachi Metals, Ltd.
FINEMET is a registered trademark of Hitachi Metals, Ltd.
3.7
Failsafe system which uses the inverter
When a fault is detected by the protective function, the protective function is activated to output a fault signal. However, a fault
signal may not be output at an inverter's fault occurrence when the detection circuit or output circuit fails, etc. Although
Mitsubishi Electric assures the best quality products, provide an interlock which uses inverter status output signals to prevent
accidents such as damage to the machine when the inverter fails for some reason. Also at the same time consider the system
configuration where a failsafe from outside the inverter, without using the inverter, is enabled even if the inverter fails.
Interlock method which uses the inverter status output signals
By combining the inverter output signals to provide an interlock as shown below, an inverter failure can be detected.
No. Interlock method
Inverter protective function
a
operation
b Inverter operating status
c Inverter running status
d Inverter running status
(a) Checking by the output of the inverter fault signal
When the inverter's protective function is activated and
the inverter trips, the fault output signal (ALM signal) is
output. (ALM signal is assigned to terminal A1B1C1 in
the initial setting).
With this signal, check that the inverter operates
properly.
In addition, negative logic can be set. (ON when the
inverter is normal, OFF when the fault occurs.)
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PRECAUTIONS FOR USE OF THE INVERTER
Countermeasure
When a motor is driven by the inverter, axial voltage is generated on the
motor shaft, which may cause electrical corrosion of the bearing in rare
cases depending on the wiring, load, operating conditions of the motor or
specific inverter settings (high carrier frequency). Contact your sales
representative to take appropriate countermeasures for the motor. The
following shows examples of countermeasures for the inverter.
• Decrease the carrier frequency.
• Provide a common mode choke
Check method
Operation check of an alarm contact.
Circuit error detection by negative
logic.
Operation ready signal check.
Logic check of the start signal and
running signal.
Logic check of the start signal and
output current.
 on the output side of the inverter.
Used signals
Fault output signal (ALM signal)
Operation ready signal (RY signal)
Start signal (STF signal, STR signal)
Running signal (RUN signal)
Start signal (STF signal, STR signal)
Output current detection signal (Y12
signal)
Inverter fault occurrence
(trip)
ALM
ON
(when output
at NC contact)
RES
Reset ON
Refer Check
to page by user
-
Refer to
page
378
375
375, 421
382, 421
OFF
OFF
ON
Reset processing
(about 1 s)
Time