Magnetic Flux Decay Output Shutoff Signal (X74 Signal) - Mitsubishi Electric FR-A720-0.4K Instruction Manual

4.15.5 Magnetic flux decay output shutoff signal (X74 signal)

Performing frequent start/stop (inching operation) with mechanical brake using output shutoff signal (MRS)
during real sensorless vector control may cause an inverter alarm (electronic thermal realy function alarm:
E.THT, etc) due to residual magnetic flux and an error in monitor output (running speed, motor torque, load
meter, torque command, torque current command, motor output).
In such a case, use magnetic flux decay output shutoff signal (X74) as output shutoff signal.
Turning X74 signal on shuts off output after decaying motor residual magnetic flux.
For the X74 signal, set "74" in any of Pr. 178 to Pr. 189 (input terminal function selection) to assign the function.
⋅
Operate a mechanical brake after turning X74 signal on.
⋅
⋅ When the MC is provided on the inverter output side, turn X74 signal on and open the MC after magnetic flux decay
operation time (refer to below) has elapsed.
Inverter output voltage shutoff timing
X74 signal
X74
Output voltage
RUN
Mechanical brake
MC on the output side
* Maximum time of magnetic flux decay operation
Motor Capacity
2.2kW or less
(Pr. 80 setting)
Magnetic flux decay
processing time
REMARKS
⋅ When performing operation other than real sensorless vector control, turning X74 signal on immediately shuts off inverter
output.
⋅ During an automatic restart after instantaneous power failure or start-time online auto tuning under real sensorless vector
control, turning X74 signal on immediately shuts off inverter output.
⋅ When some other factor affecting output shutoff (inverter alarm, MRS signal on, etc.) occurs during magnetic flux decay
operation, magnetic flux decay operation is stopped to immideately shut off output.
⋅ X74 signal can be used with the inverter assembled in and after July 2006. Check the serial number for date of manufacture.
(Refer to page 460 .)
CAUTION
⋅ Changing the terminal assignment using Pr. 178 to Pr. 189 (input terminal function selection) may affect the other functions. Make
setting after confirming the function of each terminal.
⋅ Different from MRS signal, voltage is output during magnetic flux decay processing even if X74 signal turns on.
ON
Magnetic flux decay
processing time
ON
ON
ON
ON
Do not turn off MC
during this processing time
3.7kW to 11kW
250ms 500ms
Function assignment of external terminal and control
MRS signal
MRS
*
Output voltage
ON
RUN ON
Mechanical brake
MC on the output side ON
15kW to 30kW 37kW to 55kW
800ms 900ms
ON
ON
75kW or more
1100ms
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