AI3 4-20mA Loss

What does LFF3 mean?

Loss of the 4-20 mA signal on analog input AI3. This input is typically used for speed reference, feedback, or other critical process values. Loss of this signal will cause the drive to lose its reference, potentially leading to a stop or uncontrolled operation.

• Open circuit in the 4-20mA current loop wiring between the sensor/PLC and drive AI3 input (e.g., a wire break or loose terminal).
• External sensor or PLC output module failure, causing the cessation of the 4-20mA signal generation.
• Shorted 4-20mA signal wire to ground or to another potential (e.g., 24VDC), diverting the current.
• Incorrect wiring of the 4-20mA signal (e.g., reversed polarity or connection to a voltage input terminal instead of current).
• Drive's analog input AI3 hardware failure or internal protective fuse (if applicable) for the input channel.

Click steps to track your progress.

1. 1

   Measure the current directly at the drive's AI3 input terminals (e.g., AI3+ and AI3-) using a multimeter set to the mA range.

2. 2

   Verify the external source (e.g., PLC output, sensor) is producing a 4-20mA signal by measuring it at the source terminals.

3. 3

   Inspect the shielded cable connecting the source to AI3 for continuity and insulation integrity from end to end (AI3+, AI3-, shield).

4. 4

   Confirm parameter P4-05 (AI3 input type) is correctly set to "Current" (e.g., value 1 or 2, depending on drive model) and not "Voltage".

5. 5

   If the signal is present at the source but not at the drive's AI3 terminals, replace the input card or the entire drive if the input is integrated.