Here is a video of me trying to explain the wiring.
The other thing is i am sure you have electrical noise cause i had the same problem.
Plasma lead has to be 150 mm away from any other wiring.
All wiring must be shielded and grounded, that is everything "table, controller, control box"
and use ferrite beads everywhere as well.
Ferrite all the driver wiring as well.
Ground every moving part of the table, plus controller and control box!
I am sure this will fix the ark OK signal.
From Ross.