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Siemens SINUMERIK Controller
Parameter · Intermediate · 30-120 minutes
Siemens 4503 - [TO unit : ] H number assigned more than once. Machine data is not set.
Alarm 4503 occurs when the SINUMERIK 840D detects duplicate H-numbers assigned to different edges within the same TO (tool offset) unit during data reconstruction after Power ON. This violation of unique H-number assignment rules in external CNC system mode (MD $MN_MM_EXTERN_CNC_SYSTEM = 1 or 2) indicates corrupted or improperly configured tool data in the NCK tool management database.
4503
Siemens 4503 - [TO unit : ] H number assigned more than once. Machine data is not set.
H number assigned more than once. Machine data is not set.
This error can only occur if MD10880 $MN_MM_EXTERN_CNC_SYSTEM= 1 or 2. MD10890, $MN_EXTERN_TOOLPROG_MODE bit 3 is reset (this MD becomes effective at power-on). On checking data management, it was found that various edges of the same TO unit had the same H number. MD10890 $MN_EXTERN_TOOLPROG_MODE bit 3 remains set and is not included in data management Control reaction: Alarm display.
Root Cause Summary
Alarm 4503 occurs when the SINUMERIK 840D detects duplicate H-numbers assigned to different edges within the same TO (tool offset) unit during data reconstruction after Power ON. This violation of unique H-number assignment rules in external CNC system mode (MD $MN_MM_EXTERN_CNC_SYSTEM = 1 or 2) indicates corrupted or improperly configured tool data in the NCK tool management database.
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
Access Diagnostics menu (HMI: Diagnostics → System Information → NCK Data) and navigate to Tool Management database status to identify the affected TO unit number referenced in alarm message parameter %1.
Do not modify tool data while alarm is active.
- 2
Check backup files: Verify if a clean tool database backup exists from before the corruption occurred. Review $MN_TOOL_CHANGER_TYPE and associated tool table paths (typically in /nc/progman or /user/system).
- 3
Perform NCK cold restart: Power OFF the machine, wait 30 seconds, then Power ON. Monitor alarm recurrence. If alarm persists, proceed to tool database reset.
Cold restart clears temporary NCK memory but may not resolve persistent database corruption.
- 4
Restore tool database from backup or reload tool offset table via HMI Tool Management interface, ensuring each TO unit edge has unique H-number assignment before confirming data.
Restoring data will overwrite current corrupted entries; ensure backup validity.
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