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Failsafe system which uses the inverter
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PRECAUTIONS FOR USE OF THE INVERTER
3.7 Failsafe system which uses the inverter
When a fault is detected by the protective function, the protective function activates and outputs 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 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 Check method Used signals
a
Inverter protective function
operation
Operation check of an alarm contact.
Circuit error detection by negative logic.
Fault output signal (ALM signal)
b Inverter operating status Operation ready signal check. Operation ready signal (RY signal)
c Inverter running status Logic check of the start signal and running signal.
Start signal (STF signal, STR signal)
Running signal (RUN signal)
d Inverter running status Logic check of the start signal and output current.
Start signal (STF signal, STR signal)
Output current detection signal (Y12
signal)
(a) Checking by the output of the inverter fault signal
When the inverter's protective function activates 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.)
(b) Checking the inverter operating status by the inverter
operation ready completion signal
Operation ready signal (RY signal) is output when the
inverter power is ON and the inverter becomes
operative.
Check if the RY signal is output after powering ON the
inverter.
(c) Checking the inverter operating status by the start signal
input to the inverter and inverter running signal
The inverter running signal (RUN signal) is output when
the inverter is running. (RUN signal is assigned to
terminal RUN in the initial setting.)
Check if Y12 signal is being output while inputting a start
signal to the inverter. (STF signal is a forward rotation
signal, and STR is a reverse rotation signal.) Even after
the start signal is turned OFF, the RUN signal is kept
output until the inverter makes the motor to decelerate
and to stop. For the logic check, configure a sequence
considering the inverter's deceleration time.
ON
OFF
RES
OFF
ON
Reset ON
Output frequency
ALM
(when output
at NC contact)
Inverter fault occurrence
(trip)
Time
(about 1s)
Reset processing
STF
RH
RY
ON OFF
ON OFF
ON OFF
ON
RUN
ON OFF
Time
Power
supply
Output frequency
Pr. 13 Starting
frequency
DC injection brake
operation point
DC injection
brake operation
Reset
processing