What causes Siemens SINUMERIK alarm 8120?

Parameter or machine data configuration error. Hardware fault on the NC or drive component. Part program error or illegal command. Communication fault between NC and drive or I/O modules. Software or firmware error requiring system restart.

How do I fix Siemens SINUMERIK alarm 8120?

1. Note the complete alarm text including any axis, channel, or block number values. 2. Check for related alarms active simultaneously in the SINUMERIK alarm list. 3. Power cycle the machine to clear transient faults. 4. Review the SINUMERIK machine data for parameters related to the alarm. 5. Consult the Siemens SINUMERIK alarm manual for alarm 8120 detailed remedy.

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Siemens SINUMERIK Controller

Servo/Axis · Intermediate · 30-120 minutes

Alarm 8120

Siemens 840D 8120 - Channel block following axis/spindle generic coupling

Alarm 8120 fires when the NCK generic coupling framework exceeds hardware or licensing capacity limits on the 840D control. This occurs when the number of active couplings, their assigned leading axes, or unlicensed coupling function ranges exceed the option stage capabilities configured in machine data.

Siemens SINUMERIKServo/AxisIntermediate30-120 minutes

8120

Siemens 840D 8120 - Channel block following axis/spindle generic coupling

Channel block following axis/spindle generic coupling

Root Cause Summary

Alarm 8120 fires when the NCK generic coupling framework exceeds hardware or licensing capacity limits on the 840D control. This occurs when the number of active couplings, their assigned leading axes, or unlicensed coupling function ranges exceed the option stage capabilities configured in machine data.

Safety

Refer to Siemens documentation
Ensure qualified technician performs repairs

Causes and Fixes

1
Navigate to Diagnostics > Machine Data > MD20550 and verify MaxNumOfCouplings value against your license. Check the installed option stage in Diagnostics > System Information > License.
2
In the part program or coupling configuration (typically in _N_COUPLE_DEF_MP or equivalent), count active couplings. Disable non-critical couplings by setting MD20552 (CouplingEnable) = 0 for the offending coupling index.
Disabling couplings mid-operation may cause synchronization loss; perform this during machine startup/offline.
3
If production requires all couplings, contact your Siemens representative to upgrade the option stage license or request a higher-tier SINUMERIK package.

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