What causes Siemens SINUMERIK alarm 12581?

Motion synchronous action attempting to read a variable that cannot be accessed during axis motion (non-permissible variable in WHEN condition). Incorrect variable syntax in WHEN clause - using write-protected or output-only variables instead of read-safe variables. Attempting to read system variables or axis parameters that require motion to be stopped for safe access. Variable assignment or comparison using incompatible data types in motion synchronous context. Programming error where a variable is positioned on left side of comparison when it should only be on right side.

How do I fix Siemens SINUMERIK alarm 12581?

1. Review the NC program at block %2 and identify the variable referenced in %3 within the WHEN condition - verify it is a permissible read-only variable such as $AA_OVR, $AA_FEED, or other motion-safe system variables 2. Check Siemens 840D/828D documentation for list of variables permitted in motion synchronous actions - ensure the variable is not a write-only or output parameter 3. Modify the WHEN clause syntax to move variables to the correct side of the comparison operator; variables being read must appear on the right side or as part of a valid read expression 4. Verify the variable data type is compatible with the comparison operation and that no implicit conversions are causing access violations 5. Test the corrected NC program in DRY RUN mode first before resuming production motion to confirm the alarm clears

Siemens SINUMERIK codes

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Siemens SINUMERIK Controller

Servo/Axis · Intermediate · 20-45 minutes

Alarm 12581

Siemens 840D 12581 - Channel block invalid read access to while in motion

In a motion synchronous action, the displayed variable must not be entered as a variable that is to be read on-line, i.e. 1. The displayed variable must not be written to the left of the comparison in a motion synchronous action. Only selected variables are permissible, e.g. WHEN $AA_OVR == 100 DO.

Siemens SINUMERIKServo/AxisIntermediate20-45 minutes

12581

Siemens 840D 12581 - Channel block invalid read access to while in motion

Channel block invalid read access to while in motion

Safety

Refer to Siemens documentation
Ensure qualified technician performs repairs

Common Causes

Motion synchronous action attempting to read a variable that cannot be accessed during axis motion (non-permissible variable in WHEN condition)
Incorrect variable syntax in WHEN clause - using write-protected or output-only variables instead of read-safe variables
Attempting to read system variables or axis parameters that require motion to be stopped for safe access
Variable assignment or comparison using incompatible data types in motion synchronous context
Programming error where a variable is positioned on left side of comparison when it should only be on right side

Troubleshooting Steps

1Review the NC program at block %2 and identify the variable referenced in %3 within the WHEN condition - verify it is a permissible read-only variable such as $AA_OVR, $AA_FEED, or other motion-safe system variables
2Check Siemens 840D/828D documentation for list of variables permitted in motion synchronous actions - ensure the variable is not a write-only or output parameter
3Modify the WHEN clause syntax to move variables to the correct side of the comparison operator; variables being read must appear on the right side or as part of a valid read expression
4Verify the variable data type is compatible with the comparison operation and that no implicit conversions are causing access violations
5Test the corrected NC program in DRY RUN mode first before resuming production motion to confirm the alarm clears

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