Cause : Field acknowledge comes when the drive has failed to receive a field acknowledge signal. This fault requires immediate attention, as it can impact the performance and safety of the motor.

F521 field acknowledge fault in ABB DCS800 drive indicates that the drive has detected a problem with the field current or the field supply circuit, which is essential for motor operation. 

Here’s a guide to troubleshooting and resolving this fault:

1. Power Cycle the Drive:

• Start by completely powering down the drive and then turning it back on. This can sometimes clear temporary faults.

2. Check Field Circuit Connections:

• Inspect all connections related to the field circuit. Ensure that the wiring is secure, free of corrosion, and without damage.
• Look for loose or broken wires that could interrupt the field supply.

3. Verify Field Voltage and Current:

• Use a multimeter to measure the field voltage and current. Ensure that the values are within the specified range for the motor.
• If the field voltage is not reaching the required level, it could indicate a problem with the field power supply or the drive.

4. Inspect the Field Supply:

• Check the field supply circuit for issues, such as blown fuses or tripped circuit breakers. Reset or replace any faulty components.
• Ensure that the power supply to the field is stable and capable of delivering the required current.

5. Check for Field Circuit Short or Open Conditions:

• Inspect the field winding for short circuits or open circuits. If the field winding is damaged, it will need to be repaired or replaced.
• Conduct a continuity test on the field winding to confirm it is intact.

6. Examine Drive Parameters:

• Review the field control settings in the drive parameters. Ensure that they are configured correctly for your specific motor.
• Check the field current limits set in the drive configuration. If these limits are too low, they may prevent proper operation.