Ohmic Probe Does Not Trigger

Owned by Sam Bollen, created
Mar 03, 2023
3 min read

Background

Ohmic probing relies on a calibrated resistance value between the torch cap and your workpiece.

What does proper ohmic connection look like?

Open the electrical cabinet and locate the Tormach THCT Board (PN 39096). Have a helper touch the ground clamp to the torch cap and watch LED D8 on the bottom left of the board. If the LED lights up when the ground clamp contacts the torch cap, the THCT board is measure contact between the cap and ground as intended.

Indicated: D8 LED

Switch to the Status tab in PathPilot and repeat the test with the ground clamp. Watch the status LED for ohmic touch. If it turns green when the ground clamp makes contact, the THCT board is communicating with PathPilot correctly.

Table of Contents

Check that your ground clamp is connected to your workpiece and plasma source

Reason: Faulty connection between workpiece clamp and plasma source

Ohmic probing detects continuity between the torch cap and the ground connection of the work piece. If this connection is not solid, ohmic probing will not trigger.

Check continuity between TCHT board and ground clamp

Reason: Faulty work clamp connection between plasma source and TCHT board

Continuity to the workpiece clamp is measured through the plasma source control cable Arc+ pin (since the torch operates at a negative voltage relative to the workpiece). If this connection is faulty or high resistance, the probe will not trigger.

  1. Open the electrical cabinet and locate the Tormach TCHT board (PN 39096).

  2. Using a multimeter in continuity mode, measure continuity between J2 Pin 1 (WORK) on the Tormach TCHT Board (PN 39096) and the workpiece clamp.

  3. If there is not continuity, check that the plasma source control cable is connected at the rear of the electrical cabinet. Pin 4 on this connector is used for the workpiece clamp signal.

Check connection of ohmic probe wire

Reason: Ohmic probe wire disconnected from the torch cap

  1. Check that the ohmic probe wire (481 on the electrical diagram) coming from the X-axis carriage is connected to the torch cap.

  2. Check that the connector on the read of the electrical cabinet (X27 on the electrical diagram) is connected.

To test the wire for breaks, use a multimeter in continuity mode to measure between the torch cap and Pin 5 on connector J2 (labeled CAP) on the Tormach TCHT board in the electrical cabinet.

Adjust Ohmic sensitivity

Reason: Ohmic touch sensitivity adjusted incorrectly

Read how to properly set your Ohmic Sensitivity here.

Check connection between TCHT and ECM board

Reason: TCHT board disconnected from the ECM board

  1. Open the electrical cabinet and locate the Tormach THCT board (PN 39096).

  2. Using a multimeter on continuity mode, check the connection between THCT J1 Pin 6 (PROBE-) and J9 Pin 5 on the ECM board.

  3. Perform the same check between THCT J1 Pin 7 (PROBE+) and J9 Pin 6 on the ECM board.

  4. If both connections measured good, switch the multimeter to DC Voltage mode and measure the voltage between J9 Pin 6 and 7 on the ECM board. The reading should be -3.5v without the probe tripped, and +3.5v with the probe tripped.

 

If you still are having issues, reach out to Tormach Technical Support.