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Siemens SINUMERIK Controller
Communication · Intermediate · 30-120 minutes
Siemens 28012 - NCU link: synchronization cycle signal failure times
Alarm 28012 indicates the NCU-link synchronization clock line has failed to deliver cycle signals to NCU slave modules, breaking the real-time handshake required for multi-axis coordination. This typically stems from hardware communication failures, timing parameter misconfigurations, or corruption in the NCU-link interface that prevents proper cycle synchronization between NCU 1 (master) and subordinate NCUs.
28012
Siemens 28012 - NCU link: synchronization cycle signal failure times
NCU link: synchronization cycle signal failure times
Error message of the NCU link module that does not occur at NCU 1. The NCU's are synchronized via their own NCU- link clock line. A large number of cycle signals are missing. The parameter indicates how many cycles have failed Control reaction: NC not ready. Channel not ready. NC Start disable in this channel. Interface signals are set. Alarm display. NC Stop on alarm.
Root Cause Summary
Alarm 28012 indicates the NCU-link synchronization clock line has failed to deliver cycle signals to NCU slave modules, breaking the real-time handshake required for multi-axis coordination. This typically stems from hardware communication failures, timing parameter misconfigurations, or corruption in the NCU-link interface that prevents proper cycle synchronization between NCU 1 (master) and subordinate NCUs.
Safety
- Only qualified personnel should diagnose and clear control alarms; follow the machine builder's safety procedures and lockout/tagout where hardware work is required.
Causes and Fixes
- 1
Power down the machine and visually inspect all NCU-link cables for bent pins, corrosion, loose connectors, or visible damage. Reseat both ends of the NCU-link connector firmly until you hear a click.
Ensure the control system is in OFF mode and all axes are safe before opening control cabinet.
- 2
Use an oscilloscope to measure the synchronization clock line signal amplitude and frequency at the slave NCU connector. Verify the signal maintains 5V digital levels and the cycle frequency matches the setting in MD 20080 (NCU_LINK_CYCLE_TIME).
- 3
If signal is degraded, replace the NCU-link cable with a Siemens-certified shielded twisted-pair cable (typically 6FX series). Ensure cable length does not exceed 20 meters and shield is grounded at both ends.
- 4
Power cycle the control system and monitor alarm 28012 counter in Diagnostics > Machine > NCU-Link Status menu. If counter increments slowly or stops, hardware issue is resolved.
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