SV0387 Sensor Error (Separate Detector) fault in Fanuc drive

SV0387 Sensor Error (Separate Detector) fault in Fanuc drive

Description

SV0387 is a status alarm for external scales (Linear or Rotary). Unlike a "Disconnect" or "Phase" alarm, SV0387 typically means the scale itself has entered an internal error state and raised its "Alarm" flag line to the Fanuc drive. This puts the onus of diagnosis on the scale hardware (Heidenhain, Fagor, Magnescale) rather than the Fanuc control.

Cause

• Contamination: The scale reading head cannot "see" the grating due to oil or dirt.
• Overspeed: The axis was moved faster than the scale's maximum rated read speed (common on older scales during rapid traverse).
• Low Amplitude: The light source in the scale is fading.

Solution

1. Check Scale LEDs: Many linear scale interface boxes have LED indicators. Red usually means "Dirty" or "Error."
2. Clean Scale: Follow the scale manufacturer's cleaning procedure.
3. Power Cycle: Some scales latch their error state. A full machine power down is required to reset the scale's internal CPU.