Service Home Accelerometer - Troubleshooting Guide - TG0024
Last updated: 01/27/2026

Accelerometer - Troubleshooting Guide

TG0024

Introduction

The accelerometer is a small device that can measure acceleration in one or many directions. It uses small mass on small springs to measure changes in acceleration via the change in capacitance between the two moving parts.

There are two main uses for the accelerometer on the Haas machine, vibration detection and crash detection.

Vibration detection has been around since the CHC days and is built in to the main board. 

Crash detection application has an accelerometer mounted on the spindle head, this feature was introduced in 100.21.000.1000.

Symptoms Table

Symptom Probable Cause Corrective Action
ALARM 966 EXCESSIVE TOOL IMBALANCE (board accelerometer) Excessive tool vibration is generated by on board accelerometer Verify that everything is properly balanced, such as tools and spindles

Reduce sensitivity using Setting 245

  • Setting 245 = Normal: Means that parameter 856 is directly used
  • Setting 245 = Low: Means that parameter 856 is multiplied by 1.5
  • Setting 245 = Off: Alarm 966 will not be thrown. 

NOTE: Setting 245 will not persist when the power is cycled
The Main Processor PCB standoff hardware is loose or the Control Cabinet mounting hardware is loose or causing a bind.   Tighten the Main Processor PCB standoff hardware. Loosen the Control Cabinet mounting hardware, snug the hardware, then torque down the hardware.
The tool or tool holder may be too long for the application. Longer tools are less stable than shorter tools. Always use the shortest tool possible, and remember that a 10% reduction in the length-to-diameter ratio results in a 25% increase in tool stiffness. Unless absolutely necessary, the tool's stick-out from the holder should not be more than 3 times longer than its diameter.
The spindle drive belt is worn or damaged. Check the spindle drive belt.
The encoder pulleys or drive belt are worn or damaged. Check the encoder pulleys and belt.
The toolholder is fretting. Verify the length of the tool with the manufacturer's specifications.
The drawbar force is incorrect. Make sure the drawbar clamp force is correct. Refer to: VMC - Spindle - Drawbar - Force Measurement
The fixture does not support the part. Adjust the cutting load or program.

Excessive Endmill Runout - Mill.
Tool runout should not exceed 0.0003" (0.076 mm). To check the tool runout, place a dial indicator on the tool, and then rotate the spindle by hand.
The spindle bearings are damaged. Perform a vibration analyzer.
The surface finish shows chatter, or the spindle vibrates.
ALARM 9941 CRASH DETECTED (spindle head accelerometer)  The machine detected a crash Verify the program machine movements to make sure the machine does not crash
The Accelerometer unit, cable or spindle head CAN board is damaged
  • Verify analog inputs are not 0 (cable unplugged)
  • I/O board minimum version 4.09 (update to latest if possible)
  • Spindle head CAN board minimum 1.10 (update to latest if possible
  • Make sure to take an error report (SHIFT+F3), error reports will have information about the crash direction and magnitude in the JavaConsoleLog.txt file (refer to Crash Detection Section for further information)

Vibration Detection

The vibration detection built in to the main board uses parameters 856 VIBRATION SENSOR MAX G THRESHOLD and 857 VIBRATION SENSOR HAZ COUNT THRESHOLD.

Parameter 856 is the threshold in "g" to be considered a "hazardous event."

Parameter 857 is the number of times a hazardous event must occur before an alarm can occur.

To give an example if parameter 856=1g and 857=50, this means that an alarm will occur if the sensor detects acceleration above 1g more than 50 times in a 2 second period. 

1

Vibration data can be found by pressing [DIAGNOSTIC] then navigating to the Gauges page and viewed [1].

2

Vibration data can also be found by pressing [DIAGNOSTIC] then navigating to the MOCON tab and viewing the analog data for Accelerometer X, Accelerometer Y, and Accelerometer Z [1].

Crash Detection

The accelerometer is assembled in the spindle head and interfaces with the Spindle head CAN board using the following parameters:

  • 2358 ACCELEROMETER CRASH DETECT ENABLE 
  • 2359 ACCELEROMETER CRASH THRESHOLD
  • 2360 ADC CRASH CONVERSION RATIO
  • 2361 X-AXIS ACCELEROMETER OFFSET (sets 0 point for X)
  • 2362 Y-AXIS ACCELEROMETER OFFSET (sets 0 point for Y)
  • 2363 Z-AXIS ACCELEROMETER OFFSET (sets 0 point for Z)
  • 2367 ACCELEROMETER FIR FILTER ORDER (filter signal)

These parameters work together to trigger Alarm 9941. If Parameter 2358 is enabled the control will monitor the accelerometers in the X, Y, and Z.

The following equation in the image is used to trigger Alarm 9941. If this value is greater than Parameter 2359 then the alarm will trigger.

NOTE: When safe mode is enabled and active (ie. during rapids), the alarm behavior will be suppressed so the machine can do the normal back off behavior, then the alarm will generate.  The G force value will still be recorded at the time of the event.

1

The control allows the user to view the crash accelerometer data in real time. Press [DIAGNOSTIC] then navigate to the I/O tab and view Analog input 60, 61, and 62 [1]. 

These values will show in the control as ADC and converted to mm/sec^2 in the controller using Parameter 2360. 

2

If a machine has crashed Alarm 9941 will appear on the controller.

If an error report was taken you are able to view the vector sum, which triggers this alarm if it exceeds Parameter 2359, by navigating to the JavaConsoleLog.txt in the error report.

Follow the file path as described Error Report [1] > HaasData [2] > JavaConsoleLog.txt [3]. In the JavaConsoleLog.txt file there will be a line showing the accelerometer values for the X, Y, and Z axis. There will also be the total vector value, this is the value that will trigger Parameter 2359 if exceeded.

3

The crash detection accelerometer is located in the spindle head, specifically on the Spindle mount casting as shown in the image [1].

NOTE: Pictured is a UMC-500, the orientation will vary on different machine lines. 

4

The accelerometer connects to the spindle head CAN board in the port labeled "accelerometer". 

There are several wiring configurations depending on how many CAN systems are installed on the machine. For further information please refer to our CAN Bus Systems - Troubleshooting Guide.

NOTE: Coolant intrusion or physical damage to the accelerometer, cable, or spindle head CAN board can result in nuisance 9941 alarms that will not clear with a reset.