4-20 mA Loss

What does LFF mean?

This fault occurs when the drive detects a loss of the 4-20 mA analog input signal, which is typically used for speed reference or feedback. This usually means a broken wire, a disconnected sensor, or a faulty analog signal source, causing the drive to lose its command reference and potentially stop or operate incorrectly. It can also be referred to as APL (4-20mA Loss).

• Broken wire or loose connection in the 4-20 mA analog input signal loop (e.g., terminals AI1, AI2, AIGND).
• Faulty external sensor or transducer (e.g., pressure sensor, flow meter) providing the 4-20 mA signal.
• Loss of power to the 4-20 mA sensor or the external control system supplying the signal.
• Incorrect drive parameter setting for the 4-20 mA input (e.g., minimum current level P4-10 or P4-14).
• Internal drive analog input circuit failure or component malfunction.

Click steps to track your progress.

1. 1

   1. Measure the current directly at the drive's analog input terminals (e.g., AI1 to AIGND) using a multimeter in series.

2. 2

   2. Trace the 4-20 mA wiring from the drive back to the sensor/source; check for continuity and secure connections.

3. 3

   3. Verify the power supply to the external 4-20 mA sensor or transducer.

4. 4

   4. Check Parameter P4-10 (AI1 min current) or P4-14 (AI2 min current) to ensure the drive's low-current threshold is correctly set (e.g., to 4 mA).

5. 5

   5. If possible, inject a known 4-20 mA signal from a current calibrator into the drive's analog input to test the drive's internal circuitry.