SV0448 Unmatched Feedback Alarm fault in Fanuc drive

SV0448 Unmatched Feedback Alarm fault in Fanuc drive

Description

SV0448 is a safety alarm that indicates a discrepancy in the *direction* of movement. When the amplifier outputs current to turn the motor clockwise, it expects the encoder position count to increase. If the encoder count *decreases* (moves counter-clockwise) or doesn't move at all, SV0448 is generated. It essentially means "I am pushing the gas pedal, but the car is moving backward." This prevents "runaway" conditions where positive feedback loops cause the motor to accelerate uncontrollably.

Cause

• Phasing Error (U/V/W): If the motor power cables U and V are swapped, the motor will turn the opposite direction of the magnetic field command.
• Parameter 2022: The "Motor Direction" parameter (-111 or 111) is set incorrectly for the physical mounting of the motor.
• Gravity Drop: On a vertical axis, if the brake is released before torque is applied, the axis drops. The drive commands "Up," but the encoder sees "Down."
• Encoder Mounting: The encoder was removed and re-installed, but the coupling is slipping.

Solution

1. Check Wiring: Did you recently replace the motor or cable? Verify the phase sequence (U-Red, V-White, W-Black).
2. Brake Timing: If this happens on a Z-axis at startup, the brake might be releasing too early. Adjust the brake timer parameters or check the brake for mechanical wear.
3. Parameter Check: If this is a new retrofit, try inverting the Motor Direction parameter (2022). Note: This requires a power cycle.