27100

Check HMI or operator panel for pending position acknowledgment dialog. Press the 'Acknowledge Position' or 'Confirm Reference' button on the control interface.

Do not bypass this step; acknowledgment is a safety-critical confirmation that the displayed position matches the physical axis location.

Verify MD20080 (SI: Position acknowledgment enable) is set to TRUE (1) in the Machine Data. Navigate to Diagnostics > Parameters > Machine Data > Safety > 20080.

If the acknowledgment dialog does not appear, check the PLC safety program logic in the Siemens automation tool. Verify that the safety FB (function block) for position acknowledgment is called in the cycle (typically OB 100 or the main safety OB).

Execute a follow-up reference move for the affected axis. In MDI mode, command a small move toward the reference switch (e.g., G74 with reduced feed, or a manual jog to trigger the limit switch).

Ensure the reference point is accessible and the axis can safely move. Check that the reference sensor or limit switch is functional and properly wired.

Verify parameter MD20081 (SI: Follow-up reference enable) is set correctly. If set to TRUE, follow-up referencing is mandatory. Check Diagnostics > Parameters > Machine Data > Safety > 20081.

In the Diagnostics menu, monitor the SI status signals. Verify that SI.bFollowUpRefDone becomes TRUE after the follow-up reference move completes. If it remains FALSE, check the PLC safety program and the reference sensor input signals.

If follow-up referencing is not required for your application, disable MD20081 by setting it to FALSE. This removes the follow-up reference requirement, but confirm with your safety manager that this is compliant with your machine's safety assessment.

Check the alarm history log (Diagnostics > Alarms > Archive) to identify if a safety reset or power cycle occurred before alarm 27100 appeared.

Re-execute the full referencing sequence: perform axis homing (G74 or MDI), acknowledge the machine position, and execute follow-up referencing if MD20081 is enabled.

Ensure no axes are in motion and the machine is in a safe state before initiating referencing.

Monitor the safety signal SI.bAxisRefSafe in Diagnostics > Signals > SI Signals. Confirm it transitions to TRUE after the referencing sequence is complete and acknowledged.