Cause : AI3 4-20 mA loss comes when the analog input current is below the minimum threshold value. This means loss of the 4-20 mA on analog input AI3.

An "LFF3" fault in a Schneider ATV950 drive indicate "AI3 4-20 mA loss" issue. This means the analog input (AI3), which is configured to receive a 4-20 mA signal, has lost its signal. This fault can be due to issues with the sensor, wiring, or configuration settings.

Steps to Address an "LFF3 AI3 4-20 mA Loss Fault":

1. Immediate Actions:

   • Stop Operation: If the drive is running, stop it to prevent any potential damage or unsafe conditions.
   • Reset Error: Attempt to reset the error using the drive’s control panel. This may clear temporary issues.

2. Check the Sensor:

   • Sensor Operation: Ensure that the sensor providing the 4-20 mA signal is operating correctly.
   • Power Supply: Verify that the sensor has the correct power supply and is turned on.

3. Inspect Wiring and Connections:

   • Wiring Continuity: Check the wiring between the sensor and the drive’s AI3 input for continuity. Use a multimeter to verify that there are no breaks or shorts in the wiring.
   • Connections: Ensure that all connections are secure and free from corrosion or damage. Tighten any loose connections.

4. Measure the Signal:

   • Multimeter Measurement: Use a multimeter to measure the current at the AI3 input terminal on the drive. Ensure that the signal is within the 4-20 mA range.
   • Signal Consistency: Ensure the signal is stable and not fluctuating outside the 4-20 mA range.

5. Check Configuration Settings:

   • Parameter Settings: Verify that the drive is correctly configured to accept a 4-20 mA signal on AI3. Ensure that the input is not set to another mode (e.g., 0-10 V).
   • Scaling and Filtering: Check the scaling and filtering settings for AI3 to ensure they are appropriate for your application.

6. Inspect for Electrical Noise:

   • Noise Sources: Identify and mitigate any potential sources of electrical noise that could be affecting the 4-20 mA signal. This includes ensuring proper grounding and shielding of the sensor wiring.
   • EMI/RFI Filters: Ensure that any installed EMI/RFI filters are functioning correctly and consider adding them if none are present.