PI Feedback Loss

What does FBL mean?

This fault occurs when PI Feedback Loss Detection is programmed to fault (b5-12 = 2) and the PI Feedback is below the PI Feedback Loss Detection Level (b5-13) for the PI Feedback Loss Detection Time (b5-14). The PI Feedback source (e.g., transducer, sensor, building automation signal) is not installed correctly or is not working, risking unstable control.

• Break or poor connection in the PI feedback loop wiring, causing the analog signal to drop below detection level b5-13.
• Failure of the external feedback sensor (e.g., pressure, flow, temperature) providing a zero or very low output signal.
• Incorrect setting of parameter b5-13 (PI Feedback Loss Detection Level), making it too high for normal operating conditions.
• Feedback signal range mismatch or incorrect scaling parameters (e.g., b5-05 for gain, b5-06 for offset) causing a consistently low measured signal.
• Excessive electrical noise or ground loop issues on the analog feedback input, leading to a perceived low signal level.

Click steps to track your progress.

1. 1

   Measure the raw analog feedback signal (e.g., voltage, current) directly at the sensor output and at the drive's analog input terminals (e.g., A1, AC).

2. 2

   Confirm parameter b5-12 is set to '2' (Fault) and then verify parameter b5-13 (PI Feedback Loss Detection Level) is appropriately set above 0% but below minimum expected operating signal.

3. 3

   Check for continuity and proper shielding of the feedback signal cable, particularly for open circuits or shorts to ground.

4. 4

   Temporarily apply a valid test signal (e.g., 50% of range) to the drive's analog input to test the drive's internal PI function processing.

5. 5

   Review parameters b5-05 (Feedback Gain) and b5-06 (Feedback Offset) to ensure the feedback signal is scaled correctly for the PI controller.

6. 6

   Verify the external feedback sensor is properly powered and calibrated according to its specifications.