I. Common Fault Phenomena (Quick Reference)

• No signal / No counting: No pulses from the PLC/driver, position not updated, and power-on alarm indicating 'disconnection/communication failure'.
• Inaccurate counting / Position drift: Large position deviation, poor repeatability, speed fluctuation, and pulse loss.
• Intermittent failure / Jitter: Signal intermittent, random jumps, normal operation at low speed but abnormal at high speed.
• Absolute encoder: Zero point loss upon power-on, multi-turn data loss, and low battery alarm.

II. Five-Step Diagnosis Process (Practical Operation)

1) Appearance and Mechanical Inspection (Power Off)

• Cable: Damaged insulation, crushing, bending, or tension; Connector: Looseness, pin detachment, or oxidation.
• Mechanics: Loose encoder mounting, coaxiality deviation (≤0.1mm), bushing wear, or coupling slippage.
• Environment: Oil contamination, dust, water ingress, or high temperature (contaminated light-transmitting hole of the photoelectric encoder).

2) Power Supply and Wiring Detection (Multimeter)

• Power supply: Measure the power supply terminal at DC 5V/24V with an error ≤±5%; Reverse connection, undervoltage, or overvoltage will definitely damage the encoder.
• Continuity: When power is off, measure A/B/Z, A-/B-/Z- against ground/power supply to ensure no short circuit or open circuit.
• Static level: When powered on and not rotating, the A/B phases should be at stable high/low levels (e.g., 5V/0V).
• Dynamic signal: Manually rotate the shaft slowly; the A/B phase voltage should change regularly, and the Z phase should generate one narrow pulse per revolution.

3) Oscilloscope Waveform Judgment (Core)

• Normal condition for incremental encoders: A/B phases are orthogonal square waves (90°) with stable amplitude and steep edges; the Z phase has one clean pulse per revolution.
• Abnormality judgment:
  • No waveform: Broken wiring, faulty power supply, or damaged optocoupler/code disc in the encoder.
  • Waveform distortion/glitches: Electromagnetic interference (power lines in the same conduit, no shielding, or poor grounding).
  • Phase disorder/jumps: Mechanical looseness, code disc eccentricity, or bearing damage.
  • Missing/multiple Z-phase pulses: Zero position damage or contaminated code disc.

4) Software and Upper Computer Diagnosis

• Incremental type: Monitor the pulse count on the PLC/driver; when rotating at a constant speed, the pulses should increase/decrease continuously and linearly.
• Absolute type: Read the absolute position via the driver/software; when manually rotating the shaft, the value shouldchange smoothly without jumps or jams.
• Alarm analysis: ' Disconnection/communication error/verification error' → wiring/interference issues; ' Position error/speed abnormality' → encoder/mechanical issues.

5) Replacement Method (Final Confirmation)

• Replace with an encoder of the same model: If the system returns to normal → the original encoder is faulty; if the fault persists → cable/driver/mechanical issues.
• Swap cables/channels: If the fault moves with the cable → the cable is faulty; if the fault remains on the same channel → the driver port is faulty.

III. Typical Fault Quick Judgment Table

IV. Key Distinction: Interference vs. Encoder Damage

• Interference: Waveform glitches/distortion, fault is random, and improvement is observed after moving away from the interference source, adding a magnetic ring, or improving grounding.
• Encoder damage: No waveform, fixed distortion, or permanent phase disorder; the fault persists after eliminating wiring/power supply issues, and the system returns to normal after encoder replacement.

V. Prevention Points

• Use shielded twisted-pair cables with single-ended grounding, and keep them away from power lines;
• Ensure a coaxiality of ≤0.1mm during installation and avoid impact;
• Regularly clean the light-transmitting hole of the photoelectric encoder and inspect cables and connectors.

VI. On-site Inspection Checklist (Directly Practical, Including Qualification Thresholds)