Mitsubishi Electric 800 Series Instruction Manual page 603

(G) Control parameters
Magnetic flux decay output shutoff and magnetic flux decay output
shutoff signal (X74 signal, Pr.850 = "2")
• The failure of inverter or increased error in motor may occur due to effect of the motor residual magnetic flux at the time
when the inverter output is shut off when frequent start and stop (inching operation) is repeated at the time of Real
sensorless vector control. If this is the case, set Pr.850 = "2" (magnetic flux decay output shutoff) or turn ON the magnetic
flux decay output shutoff (X74) signal to decay the magnetic flux at a stop, and then shut off the output.
• With Pr.850 = "2", deceleration starts at turning OFF of the start command, and the magnetic flux decay output shutoff is
activated when the estimated speed becomes lower than Pr.10 DC injection brake operation frequency.
• With the brake sequence function is set enabled, the magnetic flux decay output shutoff is activated when the frequency
becomes lower than 0.5 Hz or the Pr.13 Starting frequency setting, whichever smaller, during deceleration.
• Inverter output voltage shutoff timing when Pr.850 = "2"
Normal operation
Start command
(STF, STR)
Speed command
(rotation per
second)
Pr. 10 DC injection
brake operation
frequency
Magnetic flux decaying
Output voltage
RUN
RY2
Mechanical brake
MC on the output side

Maximum time for the magnetic flux decay operation
• Regardless of the Pr.850 setting, the magnetic flux decay output shutoff will operate immediately when the Magnetic flux
decay output shutoff signal (X74) is turned ON. For the X74 signal, set "74" in any of Pr.178 to Pr.189 (Input terminal
function selection) to assign the function.
• Inverter output shutoff timing with X74 signal
X74 signal
X74
Output voltage
RUN
Mechanical brake
MC on the output side

Maximum time for the magnetic flux decay operation
• Since the torque will decrease at the time of magnetic flux decay output shutoff, set up so the mechanical brake will
operate.
• Magnetic flux decay output shutoff will be canceled at the time of restart and when the Pre-excitation/servo ON (LX) signal/
External DC injection brake operation start (X13) signal is turned ON.
602
PARAMETERS
ON
Magnetic flux decay
processing time∗
ON
ON
ON
ON
ON
Do not turn OFF MC
during this period
ON
Magnetic flux decay
processing time∗
ON
ON
ON
ON
Do not turn off MC
during this processing time
During brake sequence
Start command
(STF, STR)
Speed command
(rotation per
minute)
Pr. 13 Starting
frequency or 0.5Hz
(whichever is lower)
Magnetic flux decaying
Output voltage
Mechanical brake
MC on the output side
MRS signal
MRS
Output voltage
ON
RUN ON
Mechanical brake
MC on the output side ON
ON
Magnetic flux
decay
processing time*
ON
RUN ON
RY2
ON
ON
ON
Do not turn OFF MC
during this period
ON
ON