When a fault is detected by the protective function, the protective function activates and output a Fault (ALM) signal. However, a fault signal may not be output at

an inverter's fault occurrence when the detection circuit or output circuit fails, etc. Although Mitsubishi Electric assures the best quality products, provide an

interlock which uses inverter status output signals to prevent accidents such as damage to the machine when the inverter fails for some reason. Also, at the same

time consider the system configuration where a 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 output signals to provide an interlock as shown below, an inverter failure can be detected.

Interlock method

Inverter protective function

Operation check of an alarm contact.

operation

Circuit error detection by negative logic.

Inverter operating status

Operation ready signal check.

Logic check of the start signal and running

Inverter running status

signal.

Logic check of the start signal and output

Inverter running status

current.

 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 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.

• 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.

Inverter

To the alarm detection sensor

PRECAUTIONS FOR USE OF THE INVERTER

The FR-A800 series inverter is a highly reliable product, but incorrect peripheral circuit making or operation/handling method may shorten the product life or

damage the product. Before starting operation, always recheck the following points.

• Use crimp terminals with insulation sleeves to wire the power supply and the motor.

• Application of power to the output terminals (U, V, W) of the inverter will damage the inverter. Never perform such wiring.

• After wiring, wire offcuts must not be left in the inverter.

Wire offcuts can cause an alarm, failure or malfunction. Always keep the inverter clean.

When drilling mounting holes in an enclosure etc., take caution not to allow chips and other foreign matter to enter the inverter.

• Use an appropriate cable gauge to suppress the voltage drop to 2% or less.

If the wiring distance is long between the inverter and motor, a voltage drop in the main circuit will cause the motor torque to decrease especially during the

output of a low frequency.

Refer to

page 6

for the recommended cable gauge.

• Keep the total wiring length within the specified length.

In long distance wiring, charging currents due to stray capacitance in the wiring may degrade the fast-response current limit operation or cause the equipment

on the inverter's output side to malfunction. Pay attention to the total wiring length. (Refer to Chapter 2 of the Instruction Manual (Detailed).)

• Electromagnetic wave interference

The input/output (main circuit) of the inverter includes high frequency components, which may interfere with the communication devices (such as AM radios)

used near the inverter. In this case, activate the EMC filter (turn ON the EMC filter ON/OFF connector) to minimize interference. (Refer to Chapter 3 of the

Instruction Manual (Detailed).)

Check method

Fault output (ALM) signal

Inverter operation ready (RY) signal

Start signal (STF signal, STR signal)

Inverter running (RUN) signal

Start signal (STF signal, STR signal)

Output current detection signal (Y12

signal)

Sensor

(speed, temperature,

air volume, etc.)