Mitsubishi Electric 800 Series Instruction Manual (Function page 139

NOTE
• When the automatic restart after instantaneous power failure function is selected (Pr.57 Restart coasting time ≠ "9999") and
the setting value for the number of encoder pulses is lower than the actual number of pulses, the output speed is limited with
the synchronous speed of the value of Pr.1 Maximum frequency + Pr.873.
• When a regenerative driving torque limit is applied and the speed limit function activates, the output torque may drop suddenly.
Also, when the speed limit function activates during pre-excitation operation, output phase loss (E.LF) may occur.
If the setting for the number of encoder pulses is confirmed as correct, it is recommended that Pr.873 be set to the maximum
value (400 Hz).
• Even if the set frequency is lowered after inverter operation, the speed limit value is not lowered. During deceleration, the
speed is limited at frequency command value + Pr.873.
 Deceleration check (Pr.690)
• This function can stop the inverter output when the motor is accelerated accidentally during rotation. This prevents a
malfunction due to incorrect encoder pulse settings.
• When the difference between the actual motor speed and the speed command value exceeds 2 Hz, the deceleration check
starts.
• If the motor does not decelerate within the time period set in Pr.690, the speed deviation excess detection (E.OSD) is
activated to shut off the inverter output.
Motor speed
Speed command
Fault output
(ALM)
NOTE
• The deceleration check is enabled in the speed control of the Vector control.
• If the protective function (E.OSD) is activated due to deceleration check, check whether the Pr.369 Number of encoder
pulses setting is correct.
• When the motor accelerates slowly (as a reference, when the frequency increment is less than 2 Hz/s), the protective function
may not be activated even when the motor does not decelerate.
Parameters referred to
Pr.285 Overspeed detection
Pr.369 Number of encoder
138
5. Speed Control
5.8 Avoiding motor overrunning
2Hz
Pr.690
ON
E.OSD
frequencypage 495
pulsespage 405
Motor coasting
Time