Cause : External alarm comes when an external alarm signal has been received by the drive. This typically occurs when an external device or system sends a signal to the drive to indicate an abnormal condition or require specific action. 

"Oh2" in Fuji FRENIC-VG drive indicate "External alarm". This means the drive has received an external fault signal from an external device or system connected to the drive. This alarm is typically triggered by an input from an external control system, such as a PLC (Programmable Logic Controller), sensor, or another piece of equipment, which signals the drive to stop or indicate a fault condition.

Possible Causes:

1. External Device Fault: An external device connected to the drive, such as a PLC, sensor, or safety relay, may have detected a fault or abnormal condition and sent a signal to the drive.

2. Wiring or Connection Issues: Loose, damaged, or incorrect wiring between the external device and the drive can cause false alarms or signal faults.

3. Incorrect External Input Configuration: The drive’s external input settings may be incorrectly configured, causing it to misinterpret signals from external devices.

4. Interference or Noise: Electrical noise or interference in the signal wiring can cause the drive to receive false fault signals.

5. External Stop Command: The drive may have received a stop command from an external control system due to an emergency stop, safety interlock, or other operational conditions.

Troubleshooting Steps:

1. Check External Devices:

   • Inspect the external devices connected to the drive that could be sending the fault signal. Ensure they are functioning correctly and are not in a fault condition.
   • Verify that any sensors, relays, or PLCs are working properly and sending the correct signals to the drive.

2. Inspect Wiring and Connections:

   • Check the wiring between the external devices and the drive. Ensure all connections are secure, and that there are no signs of damage, loose connections, or corrosion.
   • Verify that the signal wiring is correctly routed and shielded to minimize electrical noise and interference.

3. Review Drive Configuration:

   • Check the drive’s external input settings to ensure they are configured correctly according to the application and the signals being received from external devices.
   • Make sure that the external alarm input is correctly assigned and matches the expected signal type (e.g., normally open, normally closed).

4. Monitor for Electrical Noise:

   • Ensure that the signal cables are properly shielded and grounded to protect against electrical noise.
   • Route signal cables away from high-power cables or sources of interference that could affect the signal quality.

5. Test External Signals:

   • If possible, use a multimeter or other diagnostic tool to test the signals being sent from the external devices to the drive. Verify that the signals are within the expected range and format.

6. Check for External Stop Commands:

   • If the drive is connected to an external control system (e.g., PLC), verify whether the system is sending a stop command or other signals that could trigger the external alarm.
   • Review the logic and conditions in the external control system to ensure that stop commands or alarms are not being triggered unintentionally.