Beckhoff TwinCAT NC Error Code 0x4120

Beckhoff CNC Critical Safety

Model: TwinCAT NC | Code: 0x4120

Applicable Systems
TwinCAT NC

Symptoms

NC axis safety fault. A safety function has been triggered on the axis.

Possible Causes

  • Safety speed monitor detected excessive speed
  • Safety position limit exceeded
  • Safe torque off (STO) activated by safety PLC
  • Emergency stop pressed while axis was moving

Troubleshooting Steps

  1. Step 1: Check the equipment status and fault indicators to confirm the active fault code
    Fault indicator or HMI displays code 0x4120 as active
  2. Step 2: Verify all electrical connections, wiring harnesses, and connector seating
    All connections secure, no corrosion, loose pins, or damaged wires
  3. Step 3: Check the safety circuit continuity and all safety interlock switches
    Safety circuit complete, all interlocks engaged
  4. Step 4: Inspect the specific safety device referenced in the fault (door switch, light curtain, E-stop)
    Safety device functional, contacts clean and responsive
  5. Step 5: Verify the brake mechanism: check brake pad wear, spring tension, and air gap
    Brake pads within wear limit, spring tension correct, air gap within spec
  6. Step 6: Test the safety function by simulating the fault condition and verifying response
    Safety function responds correctly within specified time
  7. Step 7: Reset the fault after fixing the safety device or circuit: press RESET
    Fault clears and safety system returns to ready state

How to Reset

To reset: 1) Fix the safety device or circuit fault. 2) Clear the fault on the HMI or controller. 3) Press RESET. Caution: Never bypass safety devices.

Frequently Asked Questions

  • Q: What does fault code 0x4120 mean on the Beckhoff TwinCAT NC?

    Fault 0x4120 indicates a safety-related fault. A safety device or circuit has been triggered. Always investigate the root cause before resetting; never bypass safety devices.

  • Q: Can I continue operating the equipment with fault 0x4120 active?

    No. The equipment has detected a fault condition and has taken protective action (typically stopping or derating). Continuing to operate without fixing the root cause may cause further damage. Always investigate and fix the fault before resuming operation.

Related Beckhoff Fault Codes

Source: Beckhoff TwinCAT NC Error Codes (TwinCAT2_NC_Error_Codes_EN.pdf), Beckhoff Automation

Category: CNC