Excessive Speed Deviation

What does DEV mean?

This fault occurs when the actual motor speed significantly deviates from the commanded speed, particularly in applications using closed-loop control with a PG (Pulse Generator/encoder). It suggests a problem with the speed feedback device, the motor's ability to follow the command, or a tuning issue in the speed control loop. Unresolved deviation can lead to poor process control or mechanical stress.

• Encoder feedback signal loss or degradation due to damaged cable, loose connections, or a faulty encoder.
• Mechanical slip between the encoder shaft and the motor shaft, causing inaccurate speed feedback.
• Motor overload condition exceeding the inverter's current limit or the motor's torque capacity, preventing it from reaching commanded speed.
• Improperly tuned PID control loop (P-gain, I-gain, D-gain) for speed regulation (e.g., P9-XX parameters) causing oscillation or sluggish response.
• Incorrect encoder pulse count (P7-01) or motor pole count (P2-01) parameters configured in the inverter.

Click steps to track your progress.

1. 1

   Verify continuity and shielding of the encoder feedback cable from the encoder to inverter terminals (e.g., PGO, PG1, PG2).

2. 2

   Check for mechanical play or looseness in the encoder coupling to the motor shaft.

3. 3

   Monitor output current (U1-04) during operation to detect motor overload conditions.

4. 4

   Perform an auto-tuning procedure (P2-05) if available, or manually adjust speed control gains (e.g., P9-01, P9-02, P9-03) according to system response.

5. 5

   Compare commanded speed (e.g., U1-01) with actual motor speed feedback (e.g., U1-03) to quantify deviation.

6. 6

   Inspect the encoder for physical damage and test its pulse output using an oscilloscope if possible.