What causes Siemens SINUMERIK alarm 26020?

Error during initialization of encoder (refer to additional information for absolute encoder interface from error fine coding).. The alarm can be reprogrammed in the MD ALARM_REACTION_CHAN_NOREADY (channel not ready).

How do I fix Siemens SINUMERIK alarm 26020?

1. Please inform the authorized personnel/service department. 2. Rectify hardware error, replace encoder if necessary. 3. Make sure that an appropriate control module supporting this function is available with EnDat or SSI absolute encoders. 4. Bit nos. and their significance: Bit 0: Lighting failed Bit 1: Signal amplitude too small Bit 2: Position value incorrect Bit 3: Overvoltage Bit 4: Undervoltage Bit 5: Overcurrent Bit 6: Battery change necessary Bit 7: Control check error, Note: SW 4.2 and higher, synchronous linear motor Bit 8: EnDat encoder, incorrect overlapping, Note: SW 4.2 and higher, synchronous linear motor Bit 9: C/D track error on encoder ERN1387 or EQN encoder connected or incorrectly configured (not on EQN, MD 1011) Bit 10: Log cannot be aborted or old hardware Bit 11: SSI level detected on data line or no encoder connected or incorrect encoder cable (ERN instead of EQN) Bit 12: Timeout while reading measuring value Bit 13: CRC error Bit 14: Wrong IPU submodule for direct measuring signal, Note: Only with 611D expansion Bit 15: Encoder faulty Note: If an axis that is connected to the second measuring system of a controller module 611D only, is driven by an absolute encoder, the axis with the first measuring system of this controller module will have to be switched to Parking Axis, after the measuring system connector has been plugged in and prior to disabling the Parking Axis. 5. After the Parking Axis of the first measuring system has been disabled, all measuring systems of the controller module will be initialized. 6. The Parking Axis of the second measuring system can then be disabled without errors. 7. Switch control OFF - ON. 2-427

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Siemens SINUMERIK Controller

Servo/Axis · Intermediate · 30-120 minutes

Alarm 26020

Siemens 26020 - Axis encoder hardware fault during encoder initialization

Alarm 26020 occurs when the NCK fails to initialize the encoder interface during axis startup, typically due to hardware communication failures, misconfigured encoder parameters (MD20080-MD20089 range), or defective transducer feedback devices. This prevents the axis from reaching READY status and blocks channel operation until the encoder handshake completes successfully.

Siemens SINUMERIKServo/AxisIntermediate30-120 minutes

26020

Siemens 26020 - Axis encoder hardware fault during encoder initialization

Axis encoder hardware fault during encoder initialization

Root Cause Summary

Alarm 26020 occurs when the NCK fails to initialize the encoder interface during axis startup, typically due to hardware communication failures, misconfigured encoder parameters (MD20080-MD20089 range), or defective transducer feedback devices. This prevents the axis from reaching READY status and blocks channel operation until the encoder handshake completes successfully.

Safety

Drive/power/encoder circuit: hazardous voltages may remain in the DC link after power-off. Lock out / tag out, wait for discharge per the drive documentation, and use qualified personnel only.

Causes and Fixes

1
Power cycle the machine and observe if alarm 26020 repeats on the same axis. Use Diagnostics → Alarms → Active to confirm encoder %2 identifier and fault code %3 in the NCK.
Do not jog or rapid the axis while this alarm is active
2
Physically inspect the encoder connector (M23 or M12 depending on type) at both the transducer and control card for corrosion, bent pins, or loose seating. Check cable continuity with a multimeter on the signal lines referenced in the axis configuration (typically Encoder.Connector in Automation Studio hardware tree).
3
In NCK → Diagnostics → Encoders, verify the encoder type matches the hardware (MD20080 ENCODER_TYPE for the axis). Compare against the actual encoder nameplate (e.g., SSI, EnDat 2.2, DRIVE-CLiQ). If mismatch exists, correct MD20080 and perform a warm restart via Diagnostics → System Info → Restart NCK.
Incorrect encoder type will always trigger 26020 during initialization
4
If hardware appears sound, swap the encoder cable with a known-good axis cable of identical type. If alarm migrates to the other axis, the original cable is faulty. If alarm remains on the original axis, the encoder or control card input is defective and requires component replacement.

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