Mitsubishi Electric FR-A820-00046 Instruction Manual page 148

Failsafe system which uses the inverter
Backup method outside the inverter
Even if the interlock is provided by the inverter status signal, enough failsafe is not ensured depend-
ing on the failure status of the inverter itself. For example, if an inverter CPU fails in a system inter-
locked 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 im-
portance 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.
Fig. 3-15:
3 - 26
System failure
Backup method outside the inverter
Controller
Inverter
To the alarm detection sensor
Precautions for use of the inverter
Sensor
(speed, temperature,
air volume, etc.)
I001879E