F31117 Inversion Error Signals in Siemens SINAMICS V90 Drive

F31117 Inversion Error Signals A/B/R in the Siemens SINAMICS V90 Drive indicates that the drive has detected an error in the incremental encoder feedback signals. For a square-wave incremental encoder (bipolar, differential/RS-422, double-ended), each encoder channel (A, B, and R) must have a corresponding inverted signal (A*, B*, and R*). If the drive detects that the inverted signals are missing or are not the logical inverse of the corresponding signals, it generates Fault F31117 and disables operation.

This fault generally indicates a problem with the encoder, encoder cable, or encoder wiring, rather than the motor or power stage.

Possible Causes

• Faulty incremental encoder.
• Damaged encoder cable.
• Open circuit in encoder signal wiring.
• Incorrect encoder wiring.
• Missing differential signals (A*, B*, or R*).
• Short circuit between encoder signal wires.
• Incorrect encoder type installed.
• Loose encoder connector.
• Bent or damaged connector pins.
• Electrical noise or interference on encoder signals.
• Encoder supply voltage missing or incorrect.
• Faulty encoder interface circuit in the drive (less common).

Solutions

• Check the encoder and encoder cable.
• Verify that the encoder provides both the normal and inverted signals:
  • A and A*
  • B and B*
  • R and R*
• Inspect the encoder wiring for open or short circuits.
• Verify that the encoder connector is securely connected.
• Check connector pins for damage or corrosion.
• Measure the encoder supply voltage.
• Verify that the installed encoder matches the drive requirements.
• Replace the encoder cable if damaged.
• Replace the encoder if defective.
• If the encoder and wiring are confirmed good, inspect the drive's encoder interface.

Additional Information

The Siemens SINAMICS V90 uses differential encoder signals to improve noise immunity and ensure accurate motor position and speed feedback.

Fault F31117 is generated when:

• The inverted signals (A*, B*, or R*) are missing.
• The inverted signals are not electrically opposite to A, B, and R.
• The encoder feedback cannot be validated.

According to Siemens, the first corrective action is to:

• Check the encoder and encoder cable.
• Verify that the encoder outputs both the normal and corresponding inverted signals.

Unlike an Encoder Loss Fault, F31117 specifically indicates an inversion mismatch between the differential encoder signal pairs.

Common Symptoms

• Drive displays F31117 Inversion Error Signals A/B/R.
• Servo motor does not start.
• Drive trips during enable.
• Position feedback is invalid.
• Speed feedback is unavailable.
• Encoder diagnostics fail.
• Fault occurs immediately after power-up or enabling the servo.
• Intermittent trips if the encoder cable is damaged.
• Servo operation is disabled.
• Fault remains until encoder feedback is corrected.

Recommended Troubleshooting Sequence

1. Verify that the fault is F31117 Inversion Error Signals A/B/R.
2. Disconnect power and follow lockout/tagout procedures.
3. Inspect the encoder cable for physical damage.
4. Check the encoder connector for loose or bent pins.
5. Verify that the encoder provides differential signals:
   • A / A*
   • B / B*
   • R / R*
6. Measure the encoder supply voltage.
7. Check for open or short circuits in the encoder wiring.
8. Verify that the installed encoder is compatible with the SINAMICS V90.
9. Replace the encoder cable if defective.
10. Replace the encoder if it does not generate proper differential signals.
11. Restore power and clear the fault.
12. Test motor operation and encoder feedback.
13. Monitor for recurring encoder faults.
14. Inspect the drive encoder interface if the fault persists with a known-good encoder.
15. Contact Siemens technical support if necessary.

F31117 Inversion Error Signals A/B/R Check Table

Check Point	Action
Encoder	Verify correct operation
Encoder cable	Inspect for damage or open circuits
Differential signals	Verify A/A*, B/B*, and R/R* are present and complementary
Encoder connector	Check for loose or bent pins
Encoder supply voltage	Measure and verify correct value
Wiring	Check for shorts, opens, and correct pin assignment
Encoder compatibility	Confirm encoder meets V90 requirements
Drive encoder interface	Inspect if fault persists
Servo operation	Verify normal feedback after repair
Siemens technical support	Contact if the fault remains

Preventive Maintenance Tips

• Inspect encoder cables regularly for wear and mechanical damage.
• Keep encoder connectors clean, dry, and securely fastened.
• Route encoder cables separately from power cables to minimize electrical noise.
• Use shielded encoder cables with proper grounding.
• Avoid excessive bending or pulling of encoder cables.
• Periodically verify encoder feedback during preventive maintenance.
• Replace damaged encoder cables immediately.
• Use only Siemens-approved or compatible differential encoders.
• Record recurring F31117 faults to identify intermittent wiring or encoder issues.
• Protect encoder connectors from vibration and moisture.

Proper inspection of the encoder, encoder cable, A/A*, B/B*, and R/R* differential signals, encoder power supply, and drive encoder interface will help prevent recurring F31117 Inversion Error Signals A/B/R faults in Siemens SINAMICS V90 drives, ensuring accurate position feedback, reliable speed control, and dependable long-term servo system performance.