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Navigate to Diagnostics > Machine Data in SINUMERIK HMI. Verify MD 31200 (MAXNUM_D_NUMBERS) and cross-reference with the D-number allocation in the flat D-number table (typically located in NC program initialization or part of the measuring cycle subroutine library).

Do not modify MD 31200 without understanding total memory allocation; consult machine documentation for your specific model.

Locate the measuring cycle call in the active NC program block %2. Examine the _KNUM parameter assignment—check if it references a hard-coded D-number or a variable. Print the value being passed to _KNUM at runtime.

Compare the _KNUM value against the valid D-number range. For 840D systems, typical range is D0 to D(MD31200-1). If _KNUM exceeds this, manually edit the NC program to assign a valid D-number within range.

Clear the alarm, reset the channel, and re-execute the measuring cycle. Monitor for recurrence using the NCK Trace function (Diagnostics > Trace) to validate _KNUM parameter at cycle invocation.

Access the measuring cycle source code or subroutine library (typically in /NC/CYCLE/ directory or accessible via PLC Diagnostics). Note the software version stamp embedded in the cycle header comment.

Compare the cycle version against the SINUMERIK firmware/software version shown in Diagnostics > System Information. If versions differ by 2+ minor revisions, obtain the current-generation measuring cycle library from Siemens service or your OEM.

Backup the current measuring cycle, then replace it with the version-matched library. Re-initialize the NC program and verify all _KNUM assignments in the new cycle align with the active D-number table (check via Diagnostics > Table Viewer or direct MD query).

Re-run the measuring cycle. If the alarm persists, escalate to Siemens field service with cycle version history and complete alarm log export.

Export the complete Machine Data set from the 840D controller via Diagnostics > Configuration > Export (or using SINUMERIK data transfer tool). Save as a backup for comparison.

Never directly edit .md files without Siemens service guidance; use HMI or authorized commissioning software only.

Cross-check MD 31200 (MAXNUM_D_NUMBERS), MD 28100 (D_NUM_DYNAMIC_OFFSET if applicable), and any custom D-number range limits against the OEM's commissioning documentation and original machine delivery configuration.

If Machine Data has been reduced incorrectly, restore from a known-good backup or reinitialize Machine Data to OEM defaults via Diagnostics > Reset (select 'Machine Data Only' option). Re-apply any legitimate customizations afterward.

Restoring Machine Data will reset all custom parameters; document all local modifications before proceeding.

Verify the D-number allocation is restored and consistent with the measuring cycle library. Clear alarm and test the measuring cycle again.