Mitsubishi Electric 800 Series Instruction Manual page 86

 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, if an inverter CPU fails in a system interlocked with the inverter's fault, start, and RUN signals,
no fault signal will be output and the RUN signal will be kept ON because the inverter CPU is down.
Provide a speed detector to detect the motor speed and current detector to detect the motor current and consider the backup
system such as performing a check as below according to the level of importance of the system.
 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 current is flowing
through the motor while the motor coasts to stop, even after the inverter's start signal is turned OFF. For the logic check,
configure a sequence considering the inverter's deceleration time. In addition, it is recommended to check the three-phase
current when using the current detector.
 Command speed and actual operation check
Check for a gap between the actual speed and commanded speed by comparing the inverter's speed command and the speed
detected by the speed detector.
System failure
Controller
Inverter
(speed, temperature,
air volume, etc.)
To the alarm detection sensor
Sensor
3. PRECAUTIONS FOR USE OF THE INVERTER
3.7 Failsafe system which uses the inverter
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