Mitsubishi Electric FATEC FR-A800 Manual page 50

3
MAINTENANCE SYSTEM DESIGN
(2) 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 output 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.
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 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.
2) 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
To the alarm detection sensor
3.2 Failsafe system which uses the inverter
Sensor
(speed,
temperature, air
volume, etc.)
1
2
3
4
5
6
7
8
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