Fault Overview

During a scheduled restart, the Black Horse F2102 Safety-Related Application Module entered RUN mode successfully, but one safety output channel remained locked in SAFE (de-energized) state.

Observed symptoms:

• Module in RUN mode

• Three outputs functioning normally

• One output permanently OFF

• Diagnostic message: Output Feedback Error

• No short circuit detected

Production equipment connected to that channel could not start.

Understanding Safety Output Monitoring

The F2102 safety module includes:

• Redundant output driver stages

• Output state verification circuit

• External feedback monitoring (EDM)

• Discrepancy detection between command and actual state

When the module commands an output ON, it verifies that feedback matches the expected condition.

If mismatch persists, output remains disabled.

Step 1 – Read Output Diagnostic Buffer

Diagnostic message:

The module detected no confirmation from external feedback loop.

Step 2 – Verify External Device Feedback Loop

Found:

• Contactor auxiliary contact stuck open

• Mechanical wear visible

• Feedback loop never closed

Even though output driver energized, feedback signal did not confirm.

Why Output Remained Locked

Safety logic requires:

• Command ON

• Contactor closes

• Auxiliary contact confirms closure

• Feedback returns within defined time window

Because auxiliary contact failed, the module interpreted this as unsafe output state and locked channel OFF.

This prevents potential welded contact hazard.

Step 3 – Bench Test Output Driver

Measured correct output voltage when activated.

Internal driver stage confirmed healthy.

Root Cause

Mechanical failure of external contactor auxiliary feedback contact caused persistent feedback mismatch, leading to safety output lock.

Step 4 – Corrective Action

After replacement:

• Feedback signal returned correctly

• Channel enabled normally

• No further fault entries

Important Safety Note

Never bypass or short EDM feedback loop to force operation.

This defeats safety validation and violates compliance requirements.

Always repair the actual hardware cause.

Preventive Recommendations

• Periodically inspect contactor auxiliary contacts

• Replace components near mechanical life limit

• Monitor contact resistance trends

• Keep spare contactors in stock for critical circuits

Conclusion

When a Black Horse F2102 safety output remains locked despite correct RUN status, the most common cause is external device feedback failure. Proper EDM loop verification ensures safe restoration of operation in Planar F safety systems.