Prevent The Motor From Overrunning (Pr. 285, Pr. 853, Pr. 873) - Mitsubishi Electric FR-A720-0.4K Instruction Manual

4.4.7

Prevent the motor from overrunning (Pr. 285, Pr. 853, Pr. 873)

This function prevents the motor from overrunning when the load torque is too large and incorrect number of
encoder is set.
Parameter
Name
Number
Excessive speed
285 deviation detection
frequency
*1
853 Speed deviation time
*2
873 Speed limit
*2
*1 Acts as Overspeed detection frequency under encoder feed back operation. (Refer to page 208)
*2 This parameter can be set when the FR-A7AP (option) is mounted.
(1) Speed deviation excessive (Pr. 285, Pr. 853)
When the deviation between the set frequency and actual speed is large, e.g. too large load torque, this function can
cause the inverter to provide a speed deviation excessive alarm (E.OSD) and come to an alarm stop.
(2) Speed limit (Pr. 873)
This function prevents the motor from overrunning when the setting of number of encoder pulses and the actual
number differ.
When the setting of number of encoder pulses is smaller than the actual number, the motor may increase its speed.
To prevent this, restrict the output frequency with frequency (obtained by adding the set frequency and Pr. 873 ).
Actual speed
at error occurrence
CAUTION
⋅ If automatic restart after instantaneous power failure (Pr. 57 ≠ 9999) is selected when the setting of number of encoder pulses is
smaller than the actual number, the output speed is limited with the synchronous speed obtained by adding the maximum
setting (Pr. 1) and Pr. 873 setting.
⋅ When speed limit function is activated due to regenerative torque limit, output torque may suddenly decrease. In addition,
output phase error (E.LF) may occur when speed limit function is activated during pre-excitation.
When the setting of number of encoder pulses are correct, it is recommended to set a mamimum value (120Hz) in Pr. 873.
Reference parameters
Pr. 285 Overspeed detection frequency
Initial Value Setting Range
9999
9999
0 to 30Hz
1.0s 0 to 100s
20Hz 0 to 120Hz
Pr. 853
Alarm output
OFF
(across A-C)
Speed deviation
excessive error activated
(E. OSD)
Set speed + Pr. 873 value
Refer to page 208.
Speed control by real sensorless vector
Without speed deviation excessive
If the difference (absolute value) between the
speed command value and actual speed during
speed control under vector control exceeds the
Pr. 285 Excessive speed deviation detection
frequency for more than the time set in Pr. 853
Speed deviation time, speed deviation excessive
occurs and inverter error (E. OSD) appears,
resulting in a stop.
Frequency is limited at the set frequency + Pr. 873.
Set frequency
Pr. 285
Actual speed
Time
ON
Value of Pr. 873
Set speed
Speed during
normal operation.
control, vector control
Vector Vector Vector
Description
115
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