11
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 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.
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, even if the interlock is provided using the inverter fault output signal, start
signal and RUN signal output, there is a case where a fault output 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. 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.
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.
Interlock Method
Check Method
Used Signals
Refer to Page
Inverter protective function
operation
Operation check of an alarm contact
Circuit error detection by negative logic
Fault output signal
(ALM signal)
Refer to chapter
"Parameter" of the
Instruction Manual
Inverter runnning status
Operation ready signal check
Operation ready signal
(RY signal)
Logic check of the start signal and
running signal
Start signal
(STF signal, STR signal)
Running signal (RUN signal)
Logic check of the start signal and output
current
Start signal
(STF signal, STR signal)
Output current detection signal
(Y12 signal)
System failure
Controller
Inverter
Sensor
(speed, temperature,
air volume, etc.)
To the alarm detection sensor
