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FANUC Controller
Program/G-code · Intermediate · 15-30 minutes
Fanuc Alarm 142 - ILLEGAL SCALE RATE
Fanuc Alarm 142 occurs when the G51 scaling command is programmed with an invalid scale factor. The system detects a scaling rate (P value) that is either 0, negative, or equal to/greater than 10000, which are outside the permissible range for coordinate scaling. This is a program-side error that prevents execution until the scale value is corrected.
142
Fanuc Alarm 142 - ILLEGAL SCALE RATE
SYSTEM ALARM 142
Fanuc alarm 142: SYSTEM ALARM 142. This alarm indicates a fault condition detected by the Fanuc control. Refer to the alarm number and name to identify the specific system or function involved.
Root Cause Summary
Fanuc Alarm 142 occurs when the G51 scaling command is programmed with an invalid scale factor. The system detects a scaling rate (P value) that is either 0, negative, or equal to/greater than 10000, which are outside the permissible range for coordinate scaling. This is a program-side error that prevents execution until the scale value is corrected.
Causes and Fixes
- 1
Press RESET to clear the alarm. Note the program name and line number (N number) displayed when the alarm occurred.
- 2
Navigate to EDIT mode and search for G51 commands in the active program. Check the P parameter value immediately following G51 (format: G51 X__ Y__ Z__ P____). Typical valid range is P1 to P9999 where P1000 = 1.0 scale factor.
- 3
Correct the P value to a valid scaling factor. For example, P2000 = 2x scale, P500 = 0.5x scale. If scaling is not needed, remove G51 and add G50 (scale cancel) instead.
- 4
Verify parameter 5004 bit 4 (SCL) is set to 1 to enable scaling function. Navigate to SYSTEM > PARAM and check parameter 5004. If bit 4 = 0, scaling commands will cause errors.
Parameter modification requires parameter write enable (PWE) switch and may require machine restart.
Call a technician if:
- ·Parameter corruption suspected
- ·Macro programming beyond operator skill level
- ·Alarm persists after program corrections
Prevention
- Always validate G51 P values are between 0.001 and 9999.999
- Initialize macro variables with safe default values
- Use G50 to cancel scaling when not needed rather than G51 P1.0
- Implement macro variable bounds checking in custom programs
Common Mistakes
- Using G51 P0 instead of G50 to cancel scaling
- Not checking macro variable calculations for edge cases
- Copying programs between machines with different parameter settings
- Using excessive scaling factors instead of modifying CAM output
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