Failsafe system which uses the inverter
PRECAUTIONS FOR USE OF THE INVERTER
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3.6 Failsafe system which uses the inverter
When a fault is detected by the protective function, the protective function is activated 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 (ALM) signal
b Inverter operating status Operation ready signal check. Inverter operation ready (RY) signal
c Inverter running status Logic check of the start signal and running signal.
Start signal (STF signal, STR signal)
Inverter running (RUN) signal
d Inverter running status Logic check of the start signal and output current.
Start signal (STF signal, STR signal)
Output current detection (Y12) signal
(a) Checking by the output of the inverter fault signal
When the inverter's protective function is activated to
shut off the inverter output, the Fault (ALM) signal is
output. (The 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
The Inverter operation ready (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 (RUN) signal is output when the
inverter is running. (The RUN signal is assigned to
terminal RUN in the initial setting.)
Check if the Y12 signal is being output while inputting a
start signal to the inverter. (The 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 1 s)
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
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