Mitsubishi Electric 800 Series Instruction Manual page 621

(G) Control parameters
Selection of encoder feedback control (Pr.367)
• When a value other than "9999" is set in Pr. 367 Speed feedback range, encoder feedback control is valid.
Using the set point (frequency at which stable speed operation is performed) as reference, set the higher and lower setting
range. Normally, set the frequency converted from the slip amount (r/min) of the rated motor speed (rated load). If the
setting is too large, response becomes slow.
Speed feedback range
Set value
(Set command)
• For example, when the rated speed of a motor (4 poles) is 1740 r/min at 60 Hz,
Slip Nsp = Synchronous speed - Rated speed
= 1800 - 1740
= 60(r/min)
Frequency equivalent to slip (fsp) = Nsp × Number of poles/120
Feedback gain (Pr.368)
• Set Pr.368 Feedback gain when the rotation is unstable or response is slow.
• Response of the feedback will become slow when the acceleration/deceleration time is long. In such case, increase the
setting value of Pr.368.
Pr.368 setting
Pr.368 > 1 Response will become faster but it may cause overcurrent or become unstable.
1 > Pr.368 Response will become slower but it will become more stable.
Overspeed detection (Pr.285)
• To prevent malfunction when the correct pulse signal cannot be detected from the encoder, when
[detection frequency] - [output frequency]  Pr.285
at the time of encoder feedback control, protective function (E.MB1) will activate and the inverter will shutoff output.
• Overspeed detection is not performed when Pr.285 = "9999".
NOTE
• Couple the encoder on the same axis as the motor axis without any mechanical clatter, with speed ratio of 1:1.
• Encoder feedback control is not performed during the acceleration and deceleration to prevent the unstable phenomenon
such as hunting.
• Encoder feedback control is performed after the output frequency has reached [set frequency]  [speed feedback range]
once.
• When following status occurs at the time of encoder feedback control operation, inverter will not stop with an alarm, and
operate with output frequency of [set frequency]  [speed feedback range], and will not follow the speed of the motor.
- When the pulse signal from the encoder is lost due to a break, etc.
- When correct pulse signal cannot be detected due to induction noise, etc.
- When the motor is forcefully accelerated (regenerative rotation) or decelerated (motor lock) due to large external force
• Use the Inverter running (RUN) signal when releasing the brake from the motor with a brake. (The brake may not be released
when the Output frequency detection (FU) signal is used.)
• Do not turn OFF the external power supply for the encoder at the time of encoder feedback control. Correct encoder
feedback control will not be possible.
Parameters referred to
Pr.81 Number of motor poles
620
PARAMETERS
Driven load Regenerative load
= 60 × 4/120
= 2(Hz)
Description
page 137, page 426