Failsafe Of The System Which Uses The Inverter - Mitsubishi Electric 800 Series Assembly & Installation Manuallines

3 FAILSAFE OF THE SYSTEM WHICH USES THE INVERTER

When a fault is detected by the protective function, the protective function activates and output a fault signal (ALM). 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 Electric assures best quality products, provide an interlock which uses inverter status output signals to pre-
vent accidents such as damage to machine when the inverter fails for some reason.
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.
Interlock method
Inverter protective function
operation
Inverter operating status
Inverter running status
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.
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 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 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
18
Check method
Operation check of an alarm contact
Circuit error detection by negative logic
Operation ready signal check
Logic check of the start signal and running
signal
Logic check of the start signal and output
current
Controller
Inverter
Used signals
Fault output signal
(ALM signal)
Operation ready signal
(RY signal)
Start signal
(STF signal, STR signal)
Running signal (RUN signal)
Start signal
(STF signal, STR signal)
Output current detection signal
(Y12 signal)
Sensor
(speed, temperature,
air volume, etc.)
To the alarm detection sensor
Refer to
Refer to chapter
"Parameters" of the FR-A870
Instruction Manual
(Function).