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

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 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 activates and
the inverter trips, 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 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 RUN signal is being output while
inputting a start signal to the inverter. (The STF signal
is a forward rotation signal, and the 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.
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.
(when output
at NC contact)
Power
supply
STF
RUN
PRECAUTIONS FOR USE OF THE INVERTER
Failsafe system which uses the inverter
Fault (ALM) signal
Operation ready (RY) signal
Start signal (STF signal, STR signal)
Inverter running (RUN) signal
Start signal (STF signal, STR signal)
Output current detection (Y12) signal
Inverter fault occurrence
(trip)
ALM
ON OFF
ON
RES
Reset ON
ON
ON
ON
RH
Pr. 13 Starting
frequency
Reset
processing
ON
RY
ON
Used signals
Time
OFF
Reset processing
(about 1 s)
OFF
OFF
DC injection brake
operation point
DC injection
brake operation
Time
OFF
OFF
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