Proximity Sensor - How it Works and Troubleshooting Guide

How it Works

Inductive proximity sensors are non-contact electronic sensors, used to detect positions in many systems in Haas CNC machines, such as the zero or home position of an axis.

Proximity sensors use electrical power to generate an alternating magnetic field in front of the sensing face. When a metal object enters this magnetic field, the resulting disturbance activates the output driver. The I/O PCB reads the change in signal, depending on the sensor type (Normally Open (NO) or Normally Closed (NC)) and changes the monitored state of the device on the Diagnostics page.

Haas CNC machines use two- and three-wire style sensors, rated at 12 VDC and 5 VDC.

3-Wire 12 VDC (left), 3-Wire 5 VDC (right), 2-Wire 12 VDC (bottom)

Symptom Possible Cause Corrective Action Section

Positioning error or timeout alarms.

The diagnostic bit fluctuates while the monitored components are idle.

Noise or electrical interference from high-power cables. Re-route the cable away from high power sources. 1
There is a poor connection, or a signal interference from contamination. Clean, reseat connectors, and correct the cause of contamination. 2
The diagnostic bit does not change state. There is a poor connection, or a signal interference from contamination. Clean, reseat connectors, and correct cause of contamination. 2
The trip flag or the sensor is damaged or incorrectly aligned. Align the trip flag or sensor. 3
The cables or the I/O PCB is at fault. Troubleshoot the cables or the I/O PCB. 4
The proximity sensor is at fault. Check the communication between the sensor and control. 5

Section 1

Symptom: Positioning error or timeout alarms. The diagnostic bit fluctuates while the monitored components are idle.

Possible Cause: Noise or electrical interference from high-power cables.

Corrective Action:

Make sure that the proximity sensor cable is not damaged, and that it is separated from high-power spindle/axis/pump cables.

Section 2

Symptom: Positioning error or timeout alarms. The diagnostic bit fluctuates while the monitored components are idle. The diagnostic bit does not change state.

Possible Cause: There is a poor connection, or a signal interference from contamination.

Corrective Action:

Make sure that the connectors and pins for the proximity sensors are not contaminated. Make sure the pins have not backed out of the connector.

Check for contamination on the proximity sensor. Contamination on the face of the proximity sensor can create a false signal. Fix the cause of the contamination.

Section 3

Symptom: The diagnostic bit does not change state.

Possible Cause: The trip flag or the sensor is damaged or incorrectly aligned.

Corrective Action:

Put a screw in front of the face of the sensor to test its operation. If the proximity sensor LED turns on and off, and the diagnostic bit changes status, then the sensor is working correctly. Align the trip flag so that it triggers the proximity sensor.

Section 4

Symptom: The diagnostic bit does not change state.

Possible Cause: The cable is broken or the I/O PCB is at fault.

Corrective Action:

Check the proximity sensor and extenstion cables for damage.

If there is no damage to the cables, go to diy.haascnc.com to troubleshoot the I/O PCB.

Section 5

Symptom: The diagnostic bit does not change state.

Possible Cause: The proximity sensor is at fault.

Corrective Action:

For 12 VDC proximity sensors, test the voltage at the proximity sensor. The 3-wire 5 VDC sensor receives voltage from the processor PCB. It is the same voltage that is sent to the axis encoder. If the axis encoder works correctly, and there are no encoder alarms, the sensor receives the correct voltage.

Always check for voltage from the back of the connector with needle-tip probes. If there is voltage present at the proximity sensor, but it will not change status, the sensor is at fault.

N.O. 2 Wire 12V Proximity Sensor: (Black lead to ground and red lead to the brown wire)
Proximity Sensor State LED Voltage (VDC) Diagnostic Bit
Without Activation OFF 9-12 1
Activated ON 2-3 0
N.C. 2 Wire 12V Proximity Sensor: (Black lead to ground and red lead to the brown wire)
Proximity Sensor State LED Voltage (VDC) Diagnostic Bit
Without Activation ON 2-3 0
Activated OFF 9-12 1
N.O. 3 Wire 12V Proximity Sensor: (Black lead to ground and red lead to the black wire)
Proximity Sensor State LED Voltage (VDC) Diagnostic Bit
Without Activation OFF 9-12 1
Activated ON 0-2 0
N.C. 3 Wire 5V Proximity Sensor:
Proximity Sensor State LED Voltage (VDC) Diagnostic Bit
Without Activation OFF 0-2 0
Activated ON 3-5 1

Be aware: Many service and repair procedures should be done only by authorized personnel. The service technicians at your Haas Factory Outlet (HFO) have the training, experience, and are certified to do these tasks safely and correctly. You should not do machine repair or service procedures unless you are qualified and knowledgeable about the processes.

Danger: Some service procedures can be dangerous or life-threatening. DO NOT attempt a procedure that you do not completely understand. Contact your Haas Factory Outlet (HFO) and schedule a service technician visit if you have any doubts about doing a procedure.

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