Encoder Loss

What does F091 mean?

One of the two required encoder channel signals (e.g., Channel A or B for differential encoders) is missing. This deprives the drive of accurate feedback on motor speed or position, leading to unstable control, position errors, or complete shutdown in applications requiring precise motion control.

• One or both encoder feedback cables (e.g., A, B, Z channels) are disconnected or damaged, resulting in open circuits.
• Incorrect wiring of encoder differential signals (e.g., A+/A-, B+/B-) to the drive's encoder input terminals (e.g., TB3: 1, 2, 3, 4).
• Faulty encoder power supply (e.g., 5VDC or 24VDC) from the drive or external source, causing the encoder to not transmit signals.
• Encoder internal failure (e.g., LED emitter, photodetector, or ASIC) leading to no signal output.
• Excessive electrical noise on encoder signal lines due to lack of shielding or improper grounding (e.g., near motor power cables).

Click steps to track your progress.

1. 1

   1. Power down the drive, then verify continuity of each encoder feedback wire (A, /A, B, /B, Z, /Z) from the encoder to the drive's input terminals (e.g., TB3 pins) using a multimeter.

2. 2

   2. Measure the encoder power supply voltage (e.g., 5VDC or 24VDC) at the encoder connector; it must be within +/-5% of the specified voltage.

3. 3

   3. Using an oscilloscope, observe the A/B channel differential signals at the drive's encoder input terminals while the motor is slowly rotating.

4. 4

   4. Confirm encoder wiring matches the drive's terminal block schematic, especially for differential signal polarity (e.g., A+ to terminal 1, A- to terminal 2).

5. 5

   5. Temporarily disconnect the encoder cable shield from ground at the drive end and observe if fault clears (to diagnose ground loop issues).