Mitsubishi Electric FR-A820-00046 (0.4K) Instruction Manual page 261

• When the difference (absolute value) between the speed command value and actual rotation speed in speed control under
Vector control is equal to higher than the setting value in Pr.285 Speed deviation excess detection frequency for a
continuous time equal to or longer than the setting value in Pr.853 Speed deviation time, the speed deviation excess
detection (E.OSD) activates to shut off the inverter output.
Fault output
(ALM)
excessive fault activated
 Speed limit(Pr.873)
• This function prevents overrunning even when the setting value for and the value of the actual number of pulses are
different. When the setting value for the number of encoder pulses is lower than the actual number of pulses, because the
motor may increase speed, the output frequency is limited with the frequency of (set frequency + Pr.873).
Set speed + Pr. 873 value
Actual speed
at error occurrence
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)
• When performing a deceleration stop on the motor, accidental acceleration can cause the inverter to be shut off. This can
prevent a malfunction due to an incorrect encoder pulse setting, when the motor has stopped.
• When the difference between the actual motor speed and the speed command value exceeds 2 Hz after the start signal
(STF, STR) is OFF, the deceleration check starts.
• If the motor has not decelerated in the time period between the start signal (STF, STR) OFF and the Pr.690 setting, the
protective function (E.OSD) is activated to shut off the inverter output.
Motor speed
Start signal
ON
(STF, STR)
Fault output
(ALM)
260
5. PARAMETERS
5.3 Speed control under Real sensorless vector control, vector control, PM sensorless vector control
Set frequency
Pr.285
Actual speed
Time
Pr.853
OFF ON
Speed deviation
(E. OSD)
Motor coasting
Pr.690
Time
ON
E.OSD
Value of Pr. 873
Set speed
Speed during
normal operation