4-20mA loss

What does LFF mean?

This fault indicates a loss of the 4-20 mA current signal, which is typically used for speed reference, feedback, or other control inputs. This can be due to a broken wire, sensor failure, or a disconnected control device. Without a valid 4-20 mA signal, the drive may operate erratically, stop, or use a fallback value, leading to loss of critical control or incorrect motor speed.

• Break or disconnection in the 4-20mA current loop wiring to the drive's analog input (e.g., AI1).
• Failure of the 4-20mA sensor or transducer providing the signal.
• Loss of external power supply for the 4-20mA loop (if active sensor).
• Incorrect analog input configuration (e.g., P3-02, P3-03) on the drive.
• Short circuit in the 4-20mA signal wiring.

Click steps to track your progress.

1. 1

   1. Measure the current directly at the drive's analog input terminals (e.g., AI1+, AI1-) using a multimeter set to mA.

2. 2

   2. Check for continuity of the 4-20mA signal wires from the sensor/source to the drive's analog input terminals.

3. 3

   3. Verify that the 4-20mA sensor is properly powered and operating correctly at its output.

4. 4

   4. Confirm the analog input configuration parameters (e.g., P3-02, P3-03 for scaling) match the expected signal range.

5. 5

   5. Isolate the sensor and connect a known good 4-20mA source to the drive's analog input to test the drive's input circuit.