Failsafe Of The System Which Uses The Inverter - Mitsubishi Electric FR-D700 Series Instruction Manual

When a fault occurs, the inverter output is shut off to output a fault signal. 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 prevent accidents such as damage to

machine when the inverter fails for some reason and 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.

(1) 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.

No.

Interlock Method

Inverter protective

1)

function operation

2) Inverter operating status Operation ready signal check

3) Inverter running status

4) Inverter running status

(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 signal, start signal and RUN signal, there is a case where a fault 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

22

Check Method

Operation check of an alarm contact

Circuit error detection by negative logic

Logic check of the start signal and

running signal

Logic check of the start signal and

output current

Controller

Inverter

To the alarm detection sensor

Used Signals

Fault (ALM) signal

Inverter operation ready (RY) signal

Start (STF/STR) signal

Inverter running (RUN) signal

Start (STF/STR) signal

Output current detection (Y12) signal

Sensor

(speed, temperature,

air volume, etc.)

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Refer to Chapter

4 of the Instruction

Manual (Applied).

Refer to Chapter

4 of the Instruction

Manual (Applied).

Refer to Chapter

4 of the Instruction

Manual (Applied).

Refer to Chapter

4 of the Instruction

Manual (Applied).