Failsafe Of The System Which Uses The Inverter - Mitsubishi Electric 700 Series Installation Manualline

5 FAILSAFE OF THE SYSTEM WHICH USES THE
INVERTER
When a fault occurs, the inverter trips to output a fault signal. However, a fault output signal may not be output at an
inverter fault occurrence when the detection circuit or output circuit fails, etc. Although Mitsubishi Electric assures best
quality products, provide an interlock which uses inverter status output signals to prevent accidents such as damage to
machine when the inverter fails for some reason and at the same time consider the system configuration where 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 status output signals to provide an interlock as shown below, an inverter alarm can be detected.
No. Interlock Method
Inverter protective function
1)
operation
2)
3)
Inverter running status
4)
Backup method outside the inverter
Even if the interlock is provided by the inverter status signal, enough failsafe is not ensured depending on the failure status
of the inverter itself. For example, when the inverter CPU fails, even if the interlock is provided using the inverter fault
signal, start signal and RUN signal, there is a case where a fault signal is not output and RUN signal is kept output even if
an inverter fault occurs.
Provide a speed detector to detect the motor speed and current detector to detect the motor current and consider the
backup system such as checking up as below according to the level of importance of the system.
1)Start signal and actual operation check
Check the motor running and motor current while the start signal is input to the inverter by comparing the start signal
to the inverter and detected speed of the speed detector or detected current of the current detector. Note that the
motor current runs as the motor is running for the period until the motor stops since the inverter starts decelerating
even if the start signal turns off. For the logic check, configure a sequence considering the inverter deceleration time.
In addition, it is recommended to check the three-phase current when using the current detector.
2)Command speed and actual operation check
Check if there is no gap between the actual speed and commanded speed by comparing the inverter speed
command and detected speed of the speed detector.
System failure
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
Controller
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)
Sensor
(speed, temperature,
air volume, etc.)
To the alarm detection sensor
Refer to Page
Refer to Chapter 4 of
the Instruction Manual
(Applied).
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