Plasma and Ethercat?

These plots don't look correct. Try using halscope. This plot shows on piercing the arc voltage goes right off the page almost instantly then it falls below the cutting voltage before stablising around the cut voltage.
The blue line shows when the THC was enabled and you can see that the voltage has already stabilised before it comes on.


 

PCW wrote:

If you measure from the work to signal ground with a GHz capable scope at say 1ns/per division,
You will see fractional ns spikes of significant voltage on the work (or low end of divider)  
( arc starting is instantaneous an even if the current ramp is controlled, the plasma wiring
has significant capacitance)
 

Ok, yeah that can make sense. Its something I can't test so I will take you word for it. My original point was that I thought that having 500V OVP on the divided signal was an exaggeration.

This machine had a Burny controller so unfortunately no hal scope What I had was my portable scope, that's it.

If you compare my plot to yours, you have 50V/div if I look at it correctly. You can see my capture tops at around 400-450V so that would be already out of your display range? Maybe it is roughly the same?

Yeh, we don't care about the voltage until we get an Arc OK from the machine which is the pink line (comes on after the voltage peaks are gone.)
This plot is a bit atypical but its all I have saved. Usually we do not see the bump at the beginning. Perhaps that is during piercing... I think it was 8mm mild steel.