Introduction

This troubleshooting guide explains how to resolve E-stop interlock alarms on a CPX system after a power cycle. It is intended for warehouse automation and controls teams working to restore safe operation, verify circuit integrity, and confirm that PLC logic retains the correct relay state after power is restored.

Issue description

After a power cycle, the CPX system may report an E-stop interlock alarm even when the emergency stop devices appear to be reset. In many cases, the alarm is related to the E-stop circuit hardware, relay state handling in the PLC program, or a SwapState value that is not being retained in non-volatile memory.

Signs

• E-stop interlock alarm appears immediately after startup or power restoration
• The system does not clear the alarm after resetting emergency stop devices
• Relay or breaker status in the E-stop circuit does not match the expected state
• The alarm returns after each power cycle

Basic troubleshooting steps

Start with the E-stop circuit hardware and confirm that all safety devices are operating as expected.

• Verify that all breakers in the E-stop circuit are in the correct position and not tripped.
• Inspect contactors in the E-stop circuit for proper operation and signs of failure.
• Confirm that emergency stop devices are reset and that no physical safety device is still engaged.
• Check for loose wiring, damaged components, or other visible issues in the safety circuit.

Advanced troubleshooting steps

Step 1: Check the SwapState in the AOI

Review the AOI for the E-stop Interlock Relays in the PLC program and locate the SwapState value. Confirm whether the SwapState matches the expected relay state after startup.

Step 2: Confirm non-volatile memory retention

If the SwapState is not being saved to EEPROM, update the PLC logic so the value is written to non-volatile memory. Then verify that the value is retained correctly after a power cycle.

Step 3: Re-test after a controlled power cycle

After making updates, perform a controlled power cycle and confirm that the E-stop interlock alarm does not return. Verify that the relay state, alarm status, and system startup behavior are all correct.

Contact support

If the alarm continues after checking the circuit hardware and confirming SwapState retention, coordinate with your technical support team for further investigation. Be prepared to share PLC program details, alarm symptoms, and any recent changes to the E-stop circuit or control logic.

Additional information

• Use safe lockout and tagout practices before inspecting or modifying the E-stop circuit.
• Document any PLC changes so future power-cycle behavior can be traced quickly.
• If you need a site-specific procedure, request [Insert procedure name] from your technical support team.

Disclaimer

This guide is intended for qualified personnel familiar with CPX systems, PLC programming, and industrial safety circuits. Always follow site safety procedures and consult a qualified technician or technical support team when needed.