Mitsubishi Electric FR-A760 Series Instruction Manual page 63

Failsafe of the system which uses the
inverter
4) Checking the motor operating status by the start signal input to the inverter and inverter output current detection
signal.
The output current detection signal (Y12 signal) is output when the inverter operates and currents flows in the
motor. Check if Y12 signal is output when inputting the start signal to the inverter (forward signal is STF signal and
reverse signal is STR signal). Note that the current level at which Y12 signal is output is set to 150% of the inverter
rated current in the initial setting, it is necessary to adjust the level to around 20% using no load current of the
motor as reference with Pr. 150 Output current detection level.
For logic check, as same as the inverter running signal (RUN signal), the inverter outputs for the period from the
inverter decelerates until output to the motor is stopped, configure a sequence considering the inverter
deceleration time.
Output Pr. 190 to Pr. 196 Setting
Signal Positive logic Negative logic
ALM 99
RY 11
RUN 0
Y12 12
CAUTION
Changing the terminal assignment using Pr. 190 to Pr. 196 (output terminal function selection) may affect the other
functions. Make setting after confirming the function of each terminal.
(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, when the inverter CPU fails, 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.
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
52
199
111
100
112
Controller
Inverter
(speed, temperature,
To the alarm detection sensor
When using various signals, assign functions to Pr. 190 to
Pr. 196 (output terminal function selection) referring to the
table on the left.
Sensor
air volume, etc.)