Mitsubishi Electric 800 Series Instruction Manual (Function page 497

• 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
1 > Pr.368
 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
during encoder feedback control, a protective function (E.MB1) will be activated to shut off the inverter 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 unstable operation such as
hunting.
• Encoder feedback control is performed after the output frequency has reached [set frequency] ± [speed feedback range] once.
• When the following status occurs during encoder feedback control operation, the inverter output is not shut off, the output
frequency becomes the value obtained by [set frequency] ± [speed feedback range], and tracking of the motor speed is not
performed.
When Pr.376 = "0" and the pulse signal from the encoder is lost due to a break or other reasons
When correct pulse signal cannot be detected due to induction noise or other reasons
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 under encoder feedback control.
(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 during encoder feedback control. Normal encoder feedback control
will not be possible.
Parameters referred to
Pr.81 Number of motor polespage
496
17. (G) Control Parameters
17.12 Encoder feedback control
= 60 × 4/120
= 2 (Hz)
Response will become faster but it may cause overcurrent or unstable operation.
Response will become slower but the operation will become more stable.
104, page 385
Description