A115 tacho range alarm in ABB DCS800 drive indicates that the tachometer signal, which provides feedback on the motor's speed, is outside the expected range. This can lead to inaccurate speed control and potential damage to the motor.

Troubleshooting Steps:

1. Visually inspect the tachometer sensor for any signs of damage or wear.
2. Ensure that the sensor is securely mounted and properly aligned.
3. Check the wiring between the tachometer sensor and the drive for any loose connections or damage.
4. Ensure that the wiring is shielded to minimize noise interference.