What causes alarm 18 on a Mitsubishi drive?

Alarm 18 on Mitsubishi drives is caused by a communication error between the motor-side detector (encoder) and the drive unit. The causes and troubleshooting steps for this error are as follows:

1. Communication Cable Connections: Check the connections of the communication cable between the drive unit and the motor-side detector. If there is any looseness, re-secure the connectors firmly [1]. Inspect the detector connectors on the drive unit (CN2) and on the motor, disconnect and reconnect them firmly to ensure they are not loose [2].

2. Detector Cable Damage: Check the motor-side detector cable (encoder cable) for breaks, kinks, or damaged pins. If damaged, replace the cable [1]. With the power off, use a multimeter to test the detector cable for continuity and broken wires. If a fault or break in the connection is found, replace the detector cable [2].

3. Detector (Encoder) Failure: Check for a hardware failure in the detector (encoder) on the motor. If faulty, replace the detector or the motor [1]. Connect the motor's detector to another drive unit of the same capacity that is known to be working correctly. If the alarm remains on the drive unit, the input circuit of the original drive unit is faulty. If the alarm moves with the motor, the motor-side detector is faulty [2].

4. Drive Unit Failure: If the cable and motor are fine, there may be a fault in the drive unit's detector communication circuit; in this case, replace the drive unit [1]. If the alarm remains on the drive unit, the input circuit of the original drive unit is faulty [2].

5. Environmental Factors: Check for any abnormalities in the detector's environmental conditions (e.g., excessive temperature, electrical noise, grounding). Ensure the drive unit and motor are grounded at a single point, improve cable shielding, and clean or replace cooling fans if necessary [2].

6. Servo Parameter Setting (For MDS-C Drives): Check the setting of servo parameter SV025 (MTYP). If the parameter is set to '1', '5', or '9' even though an OHA type detector is not connected, correct SV025 to match the actual detector hardware (e.g., 0 for OSE104, 1 for OSA104) [2].

If the alarm persists after performing the above checks, replace the faulty drive unit or motor (detector) and contact an authorized Mitsubishi service center. If using an absolute position system, reset the zero point after replacing parts [2].