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Siemens SINUMERIK Controller
Program/G-code · Intermediate · 30-120 minutes
Siemens 840D 104126 - PA: Error on reading global basic unit
Alarm 104126 indicates the NC kernel cannot read the global basic unit definition from the system configuration. This typically occurs when the machine data (MD) defining fundamental measurement units is corrupted, missing, or contains invalid values that prevent proper initialization of the control system.
104126
Siemens 840D 104126 - PA: Error on reading global basic unit
PA: Error on reading global basic unit
Siemens SINUMERIK alarm 104126: PA: Error on reading global basic unit. This alarm indicates an error condition in the NC program or control configuration that must be resolved before the operation can continue.
Root Cause Summary
Alarm 104126 indicates the NC kernel cannot read the global basic unit definition from the system configuration. This typically occurs when the machine data (MD) defining fundamental measurement units is corrupted, missing, or contains invalid values that prevent proper initialization of the control system.
Safety
- Refer to Siemens documentation
- Ensure qualified technician performs repairs
Causes and Fixes
- 1
Access Commissioning mode and navigate to machine data settings (HMI: Commissioning → Machine Data).
- 2
Check MD10230 SCALING_SYSTEM_IS_METRIC (0=inch, 1=metric). Verify it contains a valid value (0 or 1) and is not empty or corrupted.
Document current settings before making changes. Incorrect unit settings will affect all position values.
- 3
If MD10230 shows invalid data, restore from a known good machine data backup or set to appropriate value for your machine (typically 1 for metric).
- 4
Execute a power cycle (NCK reset) and verify alarm clears. Re-run reference point procedure after restart.
Coordinate with production. All axes will require re-homing after NCK reset.
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